## Hello hls.js!

### First step: setup and support

First include `https://cdn.jsdelivr.net/hls.js/latest/hls.min.js` (or `/hls.js` for unminified) in your web page.

```html
  <script src="https://cdn.jsdelivr.net/hls.js/latest/hls.min.js"></script>
```

Invoke the following static method: `Hls.isSupported()` to check whether your browser is supporting [MediaSource Extensions](http://w3c.github.io/media-source/).

```html
  <script src="https://cdn.jsdelivr.net/hls.js/latest/hls.min.js"></script>
  <script>
    if (Hls.isSupported()) {
 	    console.log("hello hls.js!");
    }
  </script>
```

### Second step: instantiate Hls object and bind it to `<video>` element

Let's

   - create a `<video>` element
   - create a new HLS object
   - bind video element to this HLS object

```html
  <script src="https://cdn.jsdelivr.net/hls.js/latest/hls.min.js"></script>

  <video id="video"></video>
  <script>
    if (Hls.isSupported()) {
      var video = document.getElementById('video');
      var hls = new Hls();
      // bind them together
      hls.attachMedia(video);
      // MEDIA_ATTACHED event is fired by hls object once MediaSource is ready
      hls.on(Hls.Events.MEDIA_ATTACHED, function () {
		    console.log("video and hls.js are now bound together !");
      });
    }
  </script>
```

### Third step: load a manifest

You need to provide manifest URL as below:

```html
  <script src="https://cdn.jsdelivr.net/hls.js/latest/hls.min.js"></script>

  <video id="video"></video>
  <script>
    if (Hls.isSupported()) {
      var video = document.getElementById('video');
      var hls = new Hls();
      // bind them together
      hls.attachMedia(video);
      hls.on(Hls.Events.MEDIA_ATTACHED, function () {
        console.log("video and hls.js are now bound together !");
        hls.loadSource("http://my.streamURL.com/playlist.m3u8");
        hls.on(Hls.Events.MANIFEST_PARSED, function (event, data) {
          console.log("manifest loaded, found " + data.levels.length + " quality level");
        });
      });
    }
  </script>
```

### Fourth step: control through `<video>` element

Video is controlled through HTML `<video>` element.

HTMLVideoElement control and events could be used seamlessly.

```js
  video.play();
```

### Fifth step: error handling

All errors are signalled through a unique single event.

Each error is categorized by:

  - its type:
    - `Hls.ErrorTypes.NETWORK_ERROR` for network related errors
    - `Hls.ErrorTypes.MEDIA_ERROR` for media/video related errors
    - `Hls.ErrorTypes.OTHER_ERROR` for all other errors
  - its details:
    - refer to [Errors details](#Errors)
  - its fatality:
    - `false` if error is not fatal, hls.js will try to recover it
    - `true` if error is fatal, an action is required to (try to) recover it.

Full details are described [below](#Errors)

See sample code below to listen to errors:

```js
  hls.on(Hls.Events.ERROR, function (event, data) {
    var errorType = data.type;
    var errorDetails = data.details;
    var errorFatal = data.fatal;

    switch(data.details) {
      case hls.ErrorDetails.FRAG_LOAD_ERROR:
        // ....
        break;
      default:
        break;
    }
  }
```

#### Fatal Error Recovery

Hls.js provides means to 'try to' recover fatal network and media errors, through these 2 methods:

##### `hls.startLoad()`

Should be invoked to recover network error.

##### `hls.recoverMediaError()`

Should be invoked to recover media error.

##### Error recovery sample code

```js
  hls.on(Hls.Events.ERROR, function (event, data) {
    if (data.fatal) {
      switch(data.type) {
      case Hls.ErrorTypes.NETWORK_ERROR:
      // try to recover network error
        console.log("fatal network error encountered, try to recover");
        hls.startLoad();
        break;
      case Hls.ErrorTypes.MEDIA_ERROR:
        console.log("fatal media error encountered, try to recover");
        hls.recoverMediaError();
        break;
      default:
      // cannot recover
        hls.destroy();
        break;
      }
    }
  });
```

##### `hls.swapAudioCodec()`

If media error are still raised after calling `hls.recoverMediaError()`,
calling this method, could be useful to workaround audio codec mismatch.
the workflow should be:

on First Media Error : call `hls.recoverMediaError()`

if another Media Error is raised 'quickly' after this first Media Error : first call `hls.swapAudioCodec()`, then call `hls.recoverMediaError()`.

### Final step: destroying, switching between streams

`hls.destroy()` should be called to free used resources and destroy hls context.


## Fine Tuning

Configuration parameters could be provided to hls.js upon instantiation of `Hls` object.

```js
   var config = {
      autoStartLoad: true,
  	  startPosition : -1,
      capLevelToPlayerSize: false,
      debug: false,
      defaultAudioCodec: undefined,
      initialLiveManifestSize: 1,
      maxBufferLength: 30,
      maxMaxBufferLength: 600,
      maxBufferSize: 60*1000*1000,
      maxBufferHole: 0.5,
      maxSeekHole: 2,
      seekHoleNudgeDuration: 0.01,
      maxFragLookUpTolerance: 0.2,
      liveSyncDurationCount: 3,
      liveMaxLatencyDurationCount: 10,
      enableWorker: true,
      enableSoftwareAES: true,
      manifestLoadingTimeOut: 10000,
      manifestLoadingMaxRetry: 6,
      manifestLoadingRetryDelay: 500,
      manifestLoadingMaxRetryTimeout : 64000,
      startLevel: undefined,
      levelLoadingTimeOut: 10000,
      levelLoadingMaxRetry: 6,
      levelLoadingRetryDelay: 500,
      levelLoadingMaxRetryTimeout: 64000,
      fragLoadingTimeOut: 20000,
      fragLoadingMaxRetry: 6,
      fragLoadingRetryDelay: 500,
      fragLoadingMaxRetryTimeout: 64000,
      startFragPrefech: false,
      appendErrorMaxRetry: 3,
      loader: customLoader,
      fLoader: customFragmentLoader,
      pLoader: customPlaylistLoader,
      xhrSetup: XMLHttpRequestSetupCallback,
      fetchSetup: FetchSetupCallback,
      abrController: customAbrController,
      timelineController: TimelineController,
      enableCEA708Captions: true,
      stretchShortVideoTrack: false,
      forceKeyFrameOnDiscontinuity: true,
      abrEwmaFastLive: 5.0,
      abrEwmaSlowLive: 9.0,
      abrEwmaFastVoD: 4.0,
      abrEwmaSlowVoD: 15.0,
      abrEwmaDefaultEstimate: 500000,
      abrBandWidthFactor: 0.8,
      abrBandWidthUpFactor: 0.7,
      minAutoBitrate: 0
  };

  var hls = new Hls(config);
```

#### `Hls.DefaultConfig get/set`

This getter/setter allows to retrieve and override Hls default configuration.
This configuration will be applied by default to all instances.

#### `capLevelToPlayerSize`

(default: `false`)

  - if set to true, the adaptive algorithm with limit levels usable in auto-quality by the HTML video element dimensions (width and height)
  - if set to false, levels will not be limited. All available levels could be used in auto-quality mode taking only bandwidth into consideration.

#### `debug`

(default: `false`)

Setting `config.debug = true;` will turn on debug logs on JS console.

A logger object could also be provided for custom logging: `config.debug = customLogger;`.

#### `autoStartLoad`

(default: `true`)

 - if set to true, start level playlist and first fragments will be loaded automatically, after triggering of ```Hls.Events.MANIFEST_PARSED``` event
 - if set to false, an explicit API call (```hls.startLoad(startPosition=-1)```) will be needed to start quality level/fragment loading.

#### ```startPosition```
(default -1)

 - if set to -1, playback will start from initialTime=0 for VoD and according to ```liveSyncDuration/liveSyncDurationCount``` config params for Live
 - Otherwise, playback will start from predefined value. (unless stated otherwise in ```autoStartLoad=false``` mode : in that case startPosition can be overrided using ```hls.startLoad(startPosition)```).

#### `defaultAudioCodec`

(default: `undefined`)

 If audio codec is not signaled in variant manifest, or if only a stream manifest is provided, hls.js tries to guess audio codec by parsing audio sampling rate in ADTS header. If sampling rate is less or equal than 22050 Hz, then hls.js assumes it is HE-AAC, otherwise it assumes it is AAC-LC. This could result in bad guess, leading to audio decode error, ending up in media error.
 It is possible to hint default audiocodec to hls.js by configuring this value as below:
  - `mp4a.40.2` (AAC-LC) or
  - `mp4a.40.5` (HE-AAC) or
  - `undefined` (guess based on sampling rate)

#### ```initialLiveManifestSize```
(default 1)

number of segments needed to start a playback of Live stream.

#### `maxBufferLength`

(default: `30` seconds)

Maximum buffer length in seconds. If buffer length is/become less than this value, a new fragment will be loaded.
This is the guaranteed buffer length hls.js will try to reach, regardless of maxBufferSize.

#### `maxBufferSize`

(default: 60 MB)

'Minimum' maximum buffer size in bytes. If buffer size upfront is bigger than this value, no fragment will be loaded.

#### `maxBufferHole`

(default: `0.5` seconds)

'Maximum' inter-fragment buffer hole tolerance that hls.js can cope with when searching for the next fragment to load.
When switching between quality level, fragments might not be perfectly aligned.
This could result in small overlapping or hole in media buffer. This tolerance factor helps cope with this.

#### `maxSeekHole`

(default: `2` seconds)

In case playback is stalled, and a buffered range is available upfront, less than `maxSeekHole` seconds from current media position,
hls.js will jump over this buffer hole to reach the beginning of this following buffered range.
`maxSeekHole` allows to configure this jumpable threshold.

#### ```maxStarvationDelay```
(default 4s)

ABR algorithm will always try to choose a quality level that should avoid rebuffering.
In case no quality level with this criteria can be found (lets say for example that buffer length is 1s, but fetching a fragment at lowest quality is predicted to take around 2s ... ie we can forecast around 1s of rebuffering ...) then ABR algorithm will try to find a level that should guarantee less than ```maxStarvationDelay``` of buffering.

#### ```maxLoadingDelay```
(default 4s)

max video loading delay used in  automatic start level selection : in that mode ABR controller will ensure that video loading time (ie the time to fetch the first fragment at lowest quality level + the time to fetch the fragment at the appropriate quality level is less than ```maxLoadingDelay``` )

#### ```seekHoleNudgeDuration```
(default 0.01s)

In case playback is still stalling although a seek over buffer hole just occured, hls.js will seek to next buffer start + (number of consecutive stalls * `seekHoleNudgeDuration`) to try to restore playback.

#### `maxFragLookUpTolerance`

(default 0.2s)

This tolerance factor is used during fragment lookup.
Instead of checking whether buffered.end is located within [start, end] range, frag lookup will be done by checking  within [start-maxFragLookUpTolerance, end-maxFragLookUpTolerance] range.

This tolerance factor is used to cope with situations like:
```
buffered.end = 9.991
frag[0] : [0,10]
frag[1] : [10,20]
```
`buffered.end` is within `frag[0]` range, but as we are close to `frag[1]`, `frag[1]` should be choosen instead

If `maxFragLookUpTolerance = 0.2`,
this lookup will be adjusted to
```
frag[0] : [-0.2,9.8]
frag[1] : [9.8,19.8]
```
This time, `buffered.end` is within `frag[1]` range, and `frag[1]` will be the next fragment to be loaded, as expected.

#### `maxMaxBufferLength`

(default 600s)

Maximum buffer length in seconds. Hls.js will never exceed this value, even if `maxBufferSize` is not reached yet.

hls.js tries to buffer up to a maximum number of bytes (60 MB by default) rather than to buffer up to a maximum nb of seconds.
this is to mimic the browser behaviour (the buffer eviction algorithm is starting after the browser detects that video buffer size reaches a limit in bytes)

`maxBufferLength` is the minimum guaranteed buffer length that hls.js will try to achieve, even if that value exceeds the amount of bytes 60 MB of memory.
`maxMaxBufferLength` acts as a capping value, as if bitrate is really low, you could need more than one hour of buffer to fill 60 MB.

#### `liveSyncDurationCount`
(default: `3`)

edge of live delay, expressed in multiple of `EXT-X-TARGETDURATION`.
if set to 3, playback will start from fragment N-3, N being the last fragment of the live playlist.
decreasing this value is likely to cause playback stalls.

#### `liveMaxLatencyDurationCount`
(default: `Infinity`)

maximum delay allowed from edge of live, expressed in multiple of `EXT-X-TARGETDURATION`.
if set to 10, the player will seek back to `liveSyncDurationCount` whenever the next fragment to be loaded is older than N-10, N being the last fragment of the live playlist.
If set, this value must be stricly superior to `liveSyncDurationCount`
a value too close from `liveSyncDurationCount` is likely to cause playback stalls.

#### `liveSyncDuration`
(default: `undefined`)

Alternative parameter to ```liveSyncDurationCount```, expressed in seconds vs number of segments.
If defined in the configuration object, `liveSyncDuration` will take precedence over the default `liveSyncDurationCount`.
You can't define this parameter and either `liveSyncDurationCount` or `liveMaxLatencyDurationCount` in your configuration object at the same time.
A value too low (inferior to ~3 segment durations) is likely to cause playback stalls.

#### `liveMaxLatencyDuration`

(default: `undefined`)

Alternative parameter to `liveMaxLatencyDurationCount`, expressed in seconds vs number of segments.
If defined in the configuration object, `liveMaxLatencyDuration` will take precedence over the default `liveMaxLatencyDurationCount`.
If set, this value must be stricly superior to `liveSyncDuration` which must be defined as well.
You can't define this parameter and either `liveSyncDurationCount` or `liveMaxLatencyDurationCount` in your configuration object at the same time.
A value too close from `liveSyncDuration` is likely to cause playback stalls.

#### `enableWorker`

(default: `true`)

Enable WebWorker (if available on browser) for TS demuxing/MP4 remuxing, to improve performance and avoid lag/frame drops.

#### `enableSoftwareAES`

(default: `true`)

Enable to use JavaScript version AES decryption for fallback of WebCrypto API.

#### `startLevel`

(default: `undefined`)

When set, use this level as the default hls.startLevel. Keep in mind that the startLevel set with the API takes precedence over config.startLevel configuration parameter.

#### `fragLoadingTimeOut` / `manifestLoadingTimeOut` / `levelLoadingTimeOut`

(default: 60000ms for fragment / 10000ms for level and manifest)

URL Loader timeout.
A timeout callback will be triggered if loading duration exceeds this timeout.
no further action will be done : the load operation will not be cancelled/aborted.
It is up to the application to catch this event and treat it as needed.

#### `fragLoadingMaxRetry` / `manifestLoadingMaxRetry` / `levelLoadingMaxRetry`

(default: `3`)

Max number of load retries.

#### `fragLoadingMaxRetryTimeout` / `manifestLoadingMaxRetryTimeout` / `levelLoadingMaxRetryTimeout`

(default: `64000` ms)

Maximum frag/manifest/key retry timeout (in milliseconds) in case I/O errors are met.

#### `fragLoadingRetryDelay` / `manifestLoadingRetryDelay` / `levelLoadingRetryDelay`

(default: `1000` ms)

Initial delay between `XMLHttpRequest` error and first load retry (in ms).
Any I/O error will trigger retries every 500ms,1s,2s,4s,8s, ... capped to `fragLoadingMaxRetryTimeout` / `manifestLoadingMaxRetryTimeout` / `levelLoadingMaxRetryTimeout` value (exponential backoff).

Prefetch start fragment although media not attached.

#### `startFragPrefetch`

(default: `false`)

Start prefetching start fragment although media not attached yet.
Max number of append retries.

#### ```appendErrorMaxRetry```

(default: `3`)

Max number of `sourceBuffer.appendBuffer()` retry upon error.
Such error could happen in loop with UHD streams, when internal buffer is full. (Quota Exceeding Error will be triggered). In that case we need to wait for the browser to evict some data before being able to append buffer correctly.

#### `loader`

(default: standard `XMLHttpRequest`-based URL loader)

Override standard URL loader by a custom one.
Could be useful for P2P or stubbing (testing).

Use this, if you want to overwrite both the fragment and the playlist loader.

Note: If `fLoader` or `pLoader` are used, they overwrite `loader`!

```js
  var customLoader = function () {
    /**
     * Calling load() will start retrieving content located at given URL (HTTP GET).
     *
     * @param {object} context - loader context
     * @param {string} context.url - target URL
     * @param {string} context.responseType - loader response type (arraybuffer or default response type for playlist)
     * @param {number} [context.rangeStart] - start byte range offset
     * @param {number} [context.rangeEnd] - end byte range offset
     * @param {Boolean} [context.progressData] - true if onProgress should report partial chunk of loaded content
     * @param {object} config - loader config params
     * @param {number} config.maxRetry - Max number of load retries
     * @param {number} config.timeout - Timeout after which `onTimeOut` callback will be triggered (if loading is still not finished after that delay)
     * @param {number} config.retryDelay - Delay between an I/O error and following connection retry (ms). This to avoid spamming the server
     * @param {number} config.maxRetryDelay - max connection retry delay (ms)
     * @param {object} callbacks - loader callbacks
     * @param {onSuccessCallback} callbacks.onSuccess - Callback triggered upon successful loading of URL.
     * @param {onProgressCallback} callbacks.onProgress - Callback triggered while loading is in progress.
     * @param {onErrorCallback} callbacks.onError - Callback triggered if any I/O error is met while loading fragment.
     * @param {onTimeoutCallback} callbacks.onTimeout - Callback triggered if loading is still not finished after a certain duration.

      @callback onSuccessCallback
      @param response {object} - response data
      @param response.url {string} - response URL (which might have been redirected)
      @param response.data {string/arraybuffer} - response data (reponse type should be as per context.responseType)
      @param stats {object} - loading stats
      @param stats.trequest {number} - performance.now() just after load() has been called
      @param stats.tfirst {number} - performance.now() of first received byte
      @param stats.tload {number} - performance.now() on load complete
      @param stats.loaded {number} - nb of loaded bytes
      @param [stats.bw] {number} - download bandwidth in bit/s
      @param stats.total {number} - total nb of bytes
      @param context {object} - loader context

      @callback onProgressCallback
      @param stats {object} - loading stats
      @param stats.trequest {number} - performance.now() just after load() has been called
      @param stats.tfirst {number} - performance.now() of first received byte
      @param stats.loaded {number} - nb of loaded bytes
      @param [stats.total] {number} - total nb of bytes
      @param [stats.bw] {number} - current download bandwidth in bit/s (monitored by ABR controller to control emergency switch down)
      @param context {object} - loader context
      @param data {string/arraybuffer} - onProgress data (should be defined only if context.progressData === true)

      @callback onErrorCallback
      @param error {object} - error data
      @param error.code {number} - error status code
      @param error.text {string} - error description
      @param context {object} - loader context

      @callback onTimeoutCallback
      @param stats {object} - loading stats
      @param context {object} - loader context

   */
    this.load = function (context, config, callbacks) {};

    /** Abort any loading in progress. */
    this.abort = function () {};

    /** Destroy loading context. */
    this.destroy = function () {};
  }
```

#### `fLoader`

(default: `undefined`)

This enables the manipulation of the fragment loader.
Note: This will overwrite the default `loader`, as well as your own loader function (see above).

```js
  var customFragmentLoader = function() {
    // See `loader` for details.
  }
```

#### `pLoader`

(default: `undefined`)

This enables the manipulation of the playlist loader.
Note: This will overwrite the default `loader`, as well as your own loader function (see above).

```js
  var customPlaylistLoader = function() {
    // See `loader` for details.
  }
```

#### `xhrSetup`

(default: `undefined`)

`XMLHttpRequest` customization callback for default XHR based loader.

Parameter should be a function with two arguments `(xhr: XMLHttpRequest, url: string)`.
If `xhrSetup` is specified, default loader will invoke it before calling `xhr.send()`.
This allows user to easily modify/setup XHR. See example below.

```js
  var config = {
    xhrSetup: function(xhr, url) {
      xhr.withCredentials = true; // do send cookies
    }
  }
```

#### `fetchSetup`

(default: `undefined`)

`Fetch` customization callback for Fetch based loader.

Parameter should be a function with two arguments (`context` and `Request Init Params`).
If `fetchSetup` is specified and Fetch loader is used, `fetchSetup` will be triggered to instantiate [Request](https://developer.mozilla.org/fr/docs/Web/API/Request) Object.
This allows user to easily tweak Fetch loader. See example below.

```js
  var config = {
    fetchSetup: function(context, initParams) {
      // Always send cookies, even for cross-origin calls.
      initParams.credentials = 'include';
      return new Request(context.url,initParams);
    }
  }
```

#### `abrController`

(default: internal ABR controller)

Customized Adaptive Bitrate Streaming Controller.

Parameter should be a class providing 2 getters, 2 setters and a `destroy()` method:

 - get/set `nextAutoLevel`: return next auto-quality level/force next auto-quality level that should be returned (currently used for emergency switch down)
 - get/set `autoLevelCapping`: capping/max level value that could be used by ABR Controller
 - `destroy()`: should clean-up all used resources

#### `timelineController`

(default: internal track timeline controller)

Customized text track syncronization controller.

Parameter should be a class with a `destroy()` method:

 - `destroy()` : should clean-up all used resources

#### `enableCEA708Captions`

(default: `true`)

whether or not to enable CEA-708 captions

parameter should be a boolean

#### `stretchShortVideoTrack`

(default: `false`)

If a segment's video track is shorter than its audio track by > `min(maxSeekHole, maxBufferHole)`, extend the final video frame's duration to match the audio track's duration.
This helps playback continue in certain cases that might otherwise get stuck.

parameter should be a boolean

#### `forceKeyFrameOnDiscontinuity`
(default: `true`)

Whether or not to force having a key frame in the first AVC sample after a discontinuity.
If set to true, after a discontinuity, the AVC samples without any key frame will be dropped until finding one that contains a key frame.
If set to false, all AVC samples will be kept, which can help avoid holes in the stream.
Setting this parameter to false can also generate decoding weirdness when switching level or seeking.

parameter should be a boolean

#### `abrEwmaFastLive`
(default: `5.0`)

Fast bitrate Exponential moving average half-life, used to compute average bitrate for Live streams.
Half of the estimate is based on the last abrEwmaFastLive seconds of sample history.
Each of the sample is weighted by the fragment loading duration.

parameter should be a float greater than 0

#### `abrEwmaSlowLive`
(default: `9.0`)

Slow bitrate Exponential moving average half-life, used to compute average bitrate for Live streams.
Half of the estimate is based on the last abrEwmaSlowLive seconds of sample history.
Each of the sample is weighted by the fragment loading duration.

parameter should be a float greater than [abrEwmaFastLive](#abrewmafastlive)

#### `abrEwmaFastVoD`
(default: `4.0`)

Fast bitrate Exponential moving average half-life, used to compute average bitrate for VoD streams.
Half of the estimate is based on the last abrEwmaFastVoD seconds of sample history.
Each of the sample is weighted by the fragment loading duration.

parameter should be a float greater than 0

#### `abrEwmaSlowVoD`
(default: `15.0`)

Slow bitrate Exponential moving average half-life, used to compute average bitrate for VoD streams.
Half of the estimate is based on the last abrEwmaSlowVoD seconds of sample history.
Each of the sample is weighted by the fragment loading duration.

parameter should be a float greater than [abrEwmaFastVoD](#abrewmafastvod)

#### `abrEwmaDefaultEstimate`
(default: `500000`)

Default bandwidth estimate in bits/second prior to collecting fragment bandwidth samples.

parameter should be a float

#### `abrBandWidthFactor`
(default: `0.8`)

Scale factor to be applied against measured bandwidth average, to determine whether we can stay on current or lower quality level.
If `abrBandWidthFactor * bandwidth average < level.bitrate` then ABR can switch to that level providing that it is equal or less than current level.

#### `abrBandWidthUpFactor`
(default: `0.7`)

Scale factor to be applied against measured bandwidth average, to determine whether we can switch up to a higher quality level.
If `abrBandWidthUpFactor * bandwidth average < level.bitrate` then ABR can switch up to that quality level.

#### `minAutoBitrate`
(default: `0`)

Return the capping/min bandwidth value that could be used by automatic level selection algorithm.
Useful when browser or tab of the browser is not in the focus and bandwidth drops 


## Video Binding/Unbinding API

#### `hls.attachMedia(videoElement)`

Calling this method will:

 - bind videoElement and hls instance,
 - create MediaSource and set it as video source
 - once MediaSource object is successfully created, MEDIA_ATTACHED event will be fired.

#### `hls.detachMedia()`

Calling this method will:

 - unbind VideoElement from hls instance,
 - signal the end of the stream on MediaSource
 - reset video source (`video.src = ''`)

## Quality switch Control API

By default, hls.js handles quality switch automatically, using heuristics based on fragment loading bitrate and quality level bandwidth exposed in the variant manifest.
It is also possible to manually control quality swith using below API.

#### `hls.levels`

- get: Return array of available quality levels.

#### `hls.currentLevel`

- get: Return current playback quality level.
- set: Trigger an immediate quality level switch to new quality level. This will pause the video if it was playing, flush the whole buffer, and fetch fragment matching with current position and requested quality level. Then resume the video if needed once fetched fragment will have been buffered.

Set to `-1` for automatic level selection.

#### `hls.nextLevel`

- get: Return next playback quality level (playback quality level for next buffered fragment). Return `-1` if next fragment not buffered yet.
- set: Trigger a quality level switch for next fragment. This could eventually flush already buffered next fragment.

Set to `-1` for automatic level selection.

#### `hls.loadLevel`

- get: return last loaded fragment quality level.
- set: set quality level for next loaded fragment.

Set to `-1` for automatic level selection.

#### `hls.nextLoadLevel`

- get: Return quality level that will be used to load next fragment.
- set: Force quality level for next loaded fragment. Quality level will be forced only for that fragment.
After a fragment at this quality level has been loaded, `hls.loadLevel` will prevail.

#### `hls.firstLevel`

- get: First level index (index of first level appearing in Manifest. it is usually defined as start level hint for player).

#### `hls.startLevel`

- get/set: Start level index (level of first fragment that will be played back).
  - if not overrided by user: first level appearing in manifest will be used as start level.
  - if -1: automatic start level selection, playback will start from level matching download bandwidth (determined from download of first segment).

Default value is `hls.firstLevel`.

#### `hls.autoLevelEnabled`

- get: Tell whether auto level selection is enabled or not.

#### `hls.autoLevelCapping`

- get/set: Capping/max level value that could be used by ABR Controller.

Default value is `-1` (no level capping).

## Version Control

#### `Hls.version`

Static getter: return hls.js dist version number.


## Network Loading Control API

By default, hls.js will automatically start loading quality level playlists, and fragments after `Hls.Events.MANIFEST_PARSED` event has been triggered (and video element has been attached).

However if `config.autoStartLoad` is set to `false`, the following method needs to be called to manually start playlist and fragments loading:

#### ```hls.startLoad(startPosition=-1)```
Start/restart playlist/fragment loading. this is only effective if MANIFEST_PARSED event has been triggered and video element has been attached to hls object.

startPosition is the initial position in the playlist.
If startPosition is not set to -1, it allows to override default startPosition to the one you want (it will bypass hls.config.liveSync* config params for Live for example, so that user can start playback from whatever position)

#### ```hls.stopLoad()```
stop playlist/fragment loading. could be resumed later on by calling ```hls.startLoad()```

## Audio Tracks Control API

#### ```hls.audioTracks```
get : array of audio tracks exposed in manifest

#### ```hls.audioTrack```
get/set : audio track id (returned by)

## Live stream API

#### ```hls.liveSyncPosition```
get : position of live sync point (ie edge of live position minus safety delay defined by ```hls.config.liveSyncDuration```)

## Runtime Events

Hls.js fires a bunch of events, that could be registered as below:

```js
hls.on(Hls.Events.LEVEL_LOADED,function(event,data) {
  var level_duration = data.details.totalduration;
});
```

Full list of Events is available below:

  - `Hls.Events.MEDIA_ATTACHING`  - fired to attach Media to hls instance.
    -  data: { video , mediaSource }
  - `Hls.Events.MEDIA_ATTACHED`  - fired when Media has been succesfully attached to hls instance
    -  data: { video , mediaSource }
  - `Hls.Events.MEDIA_DETACHING`  - fired before detaching Media from hls instance
    -  data: { }
  - `Hls.Events.MEDIA_DETACHED`  - fired when Media has been detached from hls instance
    -  data: { }
  - `Hls.Events.MANIFEST_LOADING`  - fired to signal that a manifest loading starts
    -  data: { url : manifestURL }
  - `Hls.Events.MANIFEST_LOADED`  - fired after manifest has been loaded
    -  data: { levels : [available quality levels] , audioTracks : [ available audio tracks], url : manifestURL, stats : { trequest, tfirst, tload, mtime}}
  - `Hls.Events.MANIFEST_PARSED`  - fired after manifest has been parsed
    -  data: { levels : [ available quality levels ], firstLevel : index of first quality level appearing in Manifest }
  - `Hls.Events.LEVEL_LOADING`  - fired when a level playlist loading starts
    -  data: { url : level URL, level : id of level being loaded }
  - `Hls.Events.LEVEL_LOADED`  - fired when a level playlist loading finishes
    -  data: { details : levelDetails object, levelId : id of loaded level, stats : { trequest, tfirst, tload, mtime } }
  - `Hls.Events.LEVEL_UPDATED`  - fired when a level's details have been updated based on previous details, after it has been loaded
    -  data: { details : levelDetails object, level : id of updated level }
  - `Hls.Events.LEVEL_PTS_UPDATED`  - fired when a level's PTS information has been updated after parsing a fragment
    -  data: { details : levelDetails object, level : id of updated level, drift: PTS drift observed when parsing last fragment }
  - `Hls.Events.LEVEL_SWITCH`  - fired when a level switch is requested
    -  data: { level : id of new level, it is the index of the array `Hls.levels` }
  - `Hls.Events.KEY_LOADING`  - fired when a decryption key loading starts
    -  data: { frag : fragment object }
  - `Hls.Events.KEY_LOADED`  - fired when a decryption key loading is completed
    -  data: { frag : fragment object }
  - `Hls.Events.FRAG_LOADING`  - fired when a fragment loading starts
    -  data: { frag : fragment object }
  - `Hls.Events.FRAG_LOAD_PROGRESS`  - fired when a fragment load is in progress
    - data: { frag : fragment object with frag.loaded=stats.loaded, stats : { trequest, tfirst, loaded, total } }
  - `Hls.Events.FRAG_LOADED`  - fired when a fragment loading is completed
    -  data: { frag : fragment object, payload : fragment payload, stats : { trequest, tfirst, tload, length}}
  - `Hls.Events.FRAG_PARSING_INIT_SEGMENT` - fired when Init Segment has been extracted from fragment
    -  data: { id: demuxer id, moov : moov MP4 box, codecs : codecs found while parsing fragment}
  - `Hls.Events.FRAG_PARSING_METADATA`  - fired when parsing id3 is completed
      -  data: { id: demuxer id, samples : [ id3 pes - pts and dts timestamp are relative, values are in seconds]}
  - `Hls.Events.FRAG_PARSING_DATA`  - fired when moof/mdat have been extracted from fragment
    -  data: { id: demuxer id, moof : moof MP4 box, mdat : mdat MP4 box, startPTS : PTS of first sample, endPTS : PTS of last sample, startDTS : DTS of first sample, endDTS : DTS of last sample, type : stream type (audio or video), nb : number of samples}
  - `Hls.Events.FRAG_PARSED`  - fired when fragment parsing is completed
    -  data: { id: demuxer id}
  - `Hls.Events.FRAG_BUFFERED`  - fired when fragment remuxed MP4 boxes have all been appended into SourceBuffer
    -  data: { id: demuxer id, frag : fragment object, stats : { trequest, tfirst, tload, tparsed, tbuffered, length} }
  - `Hls.Events.FRAG_CHANGED`  - fired when fragment matching with current video position is changing
    -  data: { frag : fragment object }
  - `Hls.Events.FPS_DROP` - triggered when FPS drop in last monitoring period is higher than given threshold
    -  data: { curentDropped : nb of dropped frames in last monitoring period, currentDecoded : nb of decoded frames in last monitoring period, totalDropped : total dropped frames on this video element }
  - `Hls.Events.FPS_DROP_LEVEL_CAPPING` - triggered when FPS drop triggers auto level capping
    - data: { level: suggested new auto level capping by fps controller, droppedLevel : level has to much dropped frame will be restricted }
  - `Hls.Events.ERROR` -  Identifier for an error event
    - data: { type : error type, details : error details, fatal : is error fatal or not, other error specific data }
  - `Hls.Events.DESTROYING` -  fired when hls.js instance starts destroying. Different from MEDIA_DETACHED as one could want to detach and reattach a video to the instance of hls.js to handle mid-rolls for example.
    - data: { }


## Errors

Full list of errors is described below:

### Network Errors

  - `Hls.ErrorDetails.MANIFEST_LOAD_ERROR` - raised when manifest loading fails because of a network error
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.MANIFEST_LOAD_ERROR`, fatal : `true`, url : manifest URL, response : { code: error code, text: error text }, loader : URL loader }
  - `Hls.ErrorDetails.MANIFEST_LOAD_TIMEOUT` - raised when manifest loading fails because of a timeout
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.MANIFEST_LOAD_TIMEOUT`, fatal : `true`, url : manifest URL, loader : URL loader }
  - `Hls.ErrorDetails.MANIFEST_PARSING_ERROR` - raised when manifest parsing failed to find proper content
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.MANIFEST_PARSING_ERROR`, fatal : `true`, url : manifest URL, reason : parsing error reason }
  - `Hls.ErrorDetails.LEVEL_LOAD_ERROR` - raised when level loading fails because of a network error
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.LEVEL_LOAD_ERROR`, fatal : `true`, url : level URL, response : { code: error code, text: error text }, loader : URL loader }
  - `Hls.ErrorDetails.LEVEL_LOAD_TIMEOUT` - raised when level loading fails because of a timeout
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.LEVEL_LOAD_TIMEOUT`, fatal : `true`, url : level URL, loader : URL loader }
  - `Hls.ErrorDetails.LEVEL_SWITCH_ERROR` - raised when level switching fails
    - data: { type : `OTHER_ERROR`, details : `Hls.ErrorDetails.LEVEL_SWITCH_ERROR`, fatal : `false`, level : failed level index, reason : failure reason }
  - `Hls.ErrorDetails.FRAG_LOAD_ERROR` - raised when fragment loading fails because of a network error
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.FRAG_LOAD_ERROR`, fatal : `true` or `false`, frag : fragment object, response : { code: error code, text: error text } }
  - `Hls.ErrorDetails.FRAG_LOOP_LOADING_ERROR` - raised upon detection of same fragment being requested in loop
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.FRAG_LOOP_LOADING_ERROR`, fatal : `true` or `false`, frag : fragment object }
  - `Hls.ErrorDetails.FRAG_LOAD_TIMEOUT` - raised when fragment loading fails because of a timeout
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.FRAG_LOAD_TIMEOUT`, fatal : `true` or `false`, frag : fragment object }
  - `Hls.ErrorDetails.FRAG_PARSING_ERROR` - raised when fragment parsing fails
    - data: { type : `NETWORK_ERROR`, details : `Hls.ErrorDetails.FRAG_PARSING_ERROR`, fatal : `true` or `false`, reason : failure reason }

### Media Errors

  - `Hls.ErrorDetails.MANIFEST_INCOMPATIBLE_CODECS_ERROR` - raised when manifest only contains quality level with codecs incompatible with MediaSource Engine.
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.MANIFEST_INCOMPATIBLE_CODECS_ERROR`, fatal : `true`, url : manifest URL }
  - ```Hls.ErrorDetails.BUFFER_ADD_CODEC_ERROR``` - raised when MediaSource fails to add new sourceBuffer
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_ADD_CODEC_ERROR`, fatal : `false`, err : error raised by MediaSource, mimeType: mimeType on which the failure happened }
  - `Hls.ErrorDetails.BUFFER_APPEND_ERROR` - raised when exception is raised while calling buffer append
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_APPEND_ERROR`, fatal : `true`, frag : fragment object }
  - `Hls.ErrorDetails.BUFFER_APPENDING_ERROR` - raised when exception is raised during buffer appending
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_APPENDING_ERROR`, fatal : `false` }
  - `Hls.ErrorDetails.BUFFER_STALLED_ERROR` - raised when playback is stuck because buffer is running out of data
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_STALLED_ERROR`, fatal : `false` }
  - `Hls.ErrorDetails.BUFFER_FULL_ERROR` - raised when no data can be appended anymore in media buffer because it is full. this error is recovered automatically by performing a smooth level switching that empty buffers (without disrupting the playback) and reducing the max buffer length.
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_FULL_ERROR`, fatal : `false` }
  - `Hls.ErrorDetails.BUFFER_SEEK_OVER_HOLE` - raised after hls.js seeks over a buffer hole to unstuck the playback,
    - data: { type : `MEDIA_ERROR`, details : `Hls.ErrorDetails.BUFFER_SEEK_OVER_HOLE`, fatal : `false`, hole : hole duration }


## Objects

### Level

A `Level` object represents a given quality level.
It contains quality level related info, retrieved from manifest, such as:

* level bitrate
* used codecs
* video width/height
* level name
* level URL

See sample `Level` object below:

```js
{
  url: [ 'http://levelURL.com', 'http://levelURLfailover.com' ],
  bitrate: 246440,
  name: "240",
  codecs: "mp4a.40.5,avc1.42000d",
  width: 320,
  height: 136,
}
```

- `url` is an array that might contains several items if failover/redundant streams are found in the manifest.

### LevelDetails

A `LevelDetails` object contains level details retrieved after level playlist parsing, they are specified below:

* protocol version
* playlist type
* start sequence number
* end sequence number
* level total duration
* level fragment target duration
* array of fragments info
* is this level a live playlist or not?

See sample object below, available after corresponding `LEVEL_LOADED` event has been fired:

```js
{
  version: 3,
  type: 'VOD', // null if EXT-X-PLAYLIST-TYPE not present
  startSN: 0,
  endSN: 50,
  totalduration: 510,
  targetduration: 10,
  fragments: Array(51),
  live: false
}
```

### Fragment

The `Fragment` object contains fragment related info, such as:

* fragment URL
* fragment duration
* fragment sequence number
* fragment start offset
* level identifier

See sample object below:

```js
{
  duration: 10,
  level: 3,
  sn: 35,
  start: 30,
  url: 'http://fragURL.com'
}
```