ExoPlayer1-使用

https://google.github.io/ExoPlayer/guide-v1.html

三个重要的概念：TrackRenderer,SampleSource,DataSource

TrackRenderer

• TrackRenderer负责播放指定类型的媒体如视频，音频或文字。
• MediaCodecVideoTrackRenderer 是负责播放视频的实现
• MediaCodecAudioTrackRenderer 是负责播放音频的实现
• TextTrackRenderer 负责显示文字

MediaCodecVidoTrackRenderer和MediaCodecAudioTrackRenderer都是利用Android的MediaCodec类实现解码数据（支持的格式：https://developer.android.com/guide/appendix/media-formats.html）

ExoPlayer使用一般流程

// 1. Instantiate the player.
player = ExoPlayer.Factory.newInstance(RENDERER_COUNT);
// 2. Construct renderers.
MediaCodecVideoTrackRenderer videoRenderer = ...
MediaCodecAudioTrackRenderer audioRenderer = ...
// 3. Inject the renderers through prepare.
player.prepare(videoRenderer, audioRenderer);
// 4. Pass the surface to the video renderer.
player.sendMessage(videoRenderer, MediaCodecVideoTrackRenderer.MSG_SET_SURFACE, surface);
// 5. Start playback.
player.setPlayWhenReady(true);
...
player.release(); // Don’t forget to release when done!

SampleSource

TrackRender的构造函数需要传入一个SampleSource实例，SampleSource负责提供媒体的数据信息和格式。ExoPlayer library中提供了几种不同格式数据的SampleSource实现:

• ExtractorSampleSource- For formats such as FMP4,MP4,M4A,MKV,WebM,MP3,AAC,MPEG-TS,MPEG-PS,OGG,FLV and WAV
• ChunkSampleSource - For DASH and SmoothStreaming playbacks.
• HlsSampleSource - For HLS playbacks

DataSource

负责给SampleSource加载媒体数据，最常见的实现有：

• DefaultUriDataSource - For playing media that can be either local or loaded over the network
• AssetDataSource - For playing media stored in the assets folder of application’s apk
• ChunkSource - For DASH, 加载并提供媒体数据块

传统媒体的播放流程 （Traditional media playbacks）

传统媒体就是指：FMP4, MP4, M4A, MKV, WebM, MP3, AAC, MPEG-TS, MPEG-PS, OGG, FLV and WAV.

Allocator allocator = new DefaultAllocator(BUFFER_SEGMENT_SIZE);
DataSource dataSource = new DefaultUriDataSource(context, null, userAgent);
ExtractorSampleSource sampleSource = new ExtractorSampleSource(
    	uri, dataSource, allocator, BUFFER_SEGMENT_COUNT * BUFFER_SEGMENT_SIZE);
MediaCodecVideoTrackRenderer videoRenderer = new MediaCodecVideoTrackRenderer(
    	context, sampleSource, MediaCodecSelector.DEFAULT, MediaCodec.VIDEO_SCALING_MODE_SCALE_TO_FIT);
MediaCodecAudioTrackRenderer audioRenderer = new MediaCodecAudioTrackRenderer(
    	sampleSource, MediaCodecSelector.DEFAULT);

自适应媒体播放 （Adaptive media playbacks）

就是直播视频，选择视频清晰度的技术

自适应流媒体技术，就是能够智能感知你的下载速度，然后动态调节视频的编码速率，为你提供最高质量、最平滑的视频演播的技术。 detail

常见的技术方案有

• 苹果的HLS
• 微软的Microsoft Smooth Streaming(SmoothStreaming)
• 国际标准DASH

DASH and SmoothStreaming

ChunkSampleSource构造函数需要传入ChunkSource和LoadControl。ChuckSource providing media chunks from which to load and read samples. 有如下两种实现

• DashChunkSource：provides DASH playback using the FMP4 and WebM container formats
• SmoothStreamingChunkSource：provides SmoothStreaming playback using the FMP4 container format.

ChunkSource的实现类需要传入FormatEvaluator和DataSource

• FormatEvaluator负责管理使用的格式
• DataSource负责提供数据
• LoadControl负责处理缓冲策略

LoadControl loadControl = new DefaultLoadControl(new DefaultAllocator(BUFFER_SEGMENT_SIZE));
DefaultBandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();

// Build the video renderer.
DataSource videoDataSource = new DefaultUriDataSource(context, bandwidthMeter, userAgent);
ChunkSource videoChunkSource = new DashChunkSource(manifestFetcher,
    DefaultDashTrackSelector.newVideoInstance(context, true, false), videoDataSource,
    new AdaptiveEvaluator(bandwidthMeter), LIVE_EDGE_LATENCY_MS, elapsedRealtimeOffset, null, null,
    DemoPlayer.TYPE_VIDEO);
ChunkSampleSource videoSampleSource = new ChunkSampleSource(videoChunkSource, loadControl,
    VIDEO_BUFFER_SEGMENTS * BUFFER_SEGMENT_SIZE);
MediaCodecVideoTrackRenderer videoRenderer = new MediaCodecVideoTrackRenderer(context,
    videoSampleSource, MediaCodecSelector.DEFAULT,
    MediaCodec.VIDEO_SCALING_MODE_SCALE_TO_FIT);

// Build the audio renderer.
DataSource audioDataSource = new DefaultUriDataSource(context, bandwidthMeter, userAgent);
ChunkSource audioChunkSource = new DashChunkSource(manifestFetcher,
    DefaultDashTrackSelector.newAudioInstance(), audioDataSource, null, LIVE_EDGE_LATENCY_MS,
    elapsedRealtimeOffset, null, null, DemoPlayer.TYPE_AUDIO);
ChunkSampleSource audioSampleSource = new ChunkSampleSource(audioChunkSource,
    loadControl, AUDIO_BUFFER_SEGMENTS * BUFFER_SEGMENT_SIZE);
MediaCodecAudioTrackRenderer audioRenderer = new MediaCodecAudioTrackRenderer(
    audioSampleSource, MediaCodecSelector.DEFAULT);

In this code, manifestFetcher is an object responsible for loading the DASH manifest that defines the media. The videoAdaptationSetIndex and audioAdaptationSetIndex variables index components of the initially loaded manifest that correspond to video and audio respectively.

HLS

HLS播放需要使用到HlsSampleSource,HlsChunkSource

example:

LoadControl loadControl = new DefaultLoadControl(new DefaultAllocator(BUFFER_SEGMENT_SIZE));
DefaultBandwidthMeter bandwidthMeter = new DefaultBandwidthMeter();
PtsTimestampAdjusterProvider timestampAdjusterProvider = new PtsTimestampAdjusterProvider();
DataSource dataSource = new DefaultUriDataSource(context, bandwidthMeter, userAgent);
HlsChunkSource chunkSource = new HlsChunkSource(true /* isMaster */, dataSource, url, manifest,
    DefaultHlsTrackSelector.newDefaultInstance(context), bandwidthMeter, timestampAdjusterProvider,
    HlsChunkSource.ADAPTIVE_MODE_SPLICE);
HlsSampleSource sampleSource = new HlsSampleSource(chunkSource, loadControl,
    MAIN_BUFFER_SEGMENTS * BUFFER_SEGMENT_SIZE);
MediaCodecVideoTrackRenderer videoRenderer = new MediaCodecVideoTrackRenderer(context, sampleSource,
    MediaCodecSelector.DEFAULT, MediaCodec.VIDEO_SCALING_MODE_SCALE_TO_FIT);
MediaCodecAudioTrackRenderer audioRenderer = new MediaCodecAudioTrackRenderer(sampleSource,
    MediaCodecSelector.DEFAULT);

notes

好像只有自适应媒体的播放才有loadControl控制缓冲策略，传统媒体都是直接播放

视频播放的相关协议