Audio/Video

Everything you need to know about audio/video inside Chromium and Chromium OS!

Whom To Contact

It's best to have discussions on chromium-dev@chromium.org.

We are component Internals>Media on the Chromium bug tracker.

Documentation

Here's our outdated design doc for HTML5 audio/video.

Codec, Containers and File Extensions Support

Container formats
  • Ogg
  • WebM
  • WAV
  • MP4 (QuickTime/ MOV / MPEG4) [Google Chrome only]
Codec formats

Audio
  • FLAC
  • Opus
  • PCM 8-bit unsigned integer
  • PCM 16-bit signed integer little endian
  • PCM 32-bit float little endian
  • Vorbis
  • MP3 [Google Chrome only]
  • AAC [Main, LC, HE profiles only] [Google Chrome only]
  • AMR-NB [Google Chrome OS only]
  • AMR-WB [Google Chrome OS only]
  • PCM μ-law [Google Chrome OS only]
  • GSM [Google Chrome OS Only]
Video
  • VP8
  • VP9
  • Theora [Except on Android variants]
  • H.264 [Google Chrome only]
  • MPEG-4 [Google Chrome OS only]
File Extensions [defined in src/net/base/mime_util.cc]
  • .flac
  • .ogv
  • .ogm
  • .ogg
  • .oga
  • .opus
  • .webm
  • .wav
  • .mp4 [Google Chrome only]
  • .m4v [Google Chrome only]
  • .m4a [Google Chrome only]
  • .mp3 [Google Chrome only]
  • .amr [Google Chrome OS only]
  • .avi [Google Chrome OS only]
  • .3gp [Google Chrome OS only]

Code Location

Chromium
media/ - Home to all things media!
media/audio - OS audio input/output abstractions
media/video/capture - OS camera input abstraction
media/video - software/hardware video decoder interfaces + implementations
third_party/ffmpeg - Chromium's copy of FFmpeg
third_party/libvpx - Chromium's copy of libvpx

Blink
Source/core/html/HTMLMediaElement.{cpp,h,idl} - media element base class
Source/core/html/HTMLAudioElement.{cpp,h,idl} - audio element implementation
Source/core/html/HTMLVideoElement.{cpp,h,idl} - video element implementation

Particularly Interesting Bits
net/base/mime_util.cc - defines canPlayType() behaviour and file extension mapping
media/blink/buffered_data_source.{cc,h} - Chromium's main implementation of DataSource for the media pipeline
media/blink/buffered_resource_loader.{cc,h} - Implements the sliding window buffering strategy (see below)
third_party/WebKit/public/platform/WebMediaPlayer.h - Blink's media player interface for providing HTML5 audio/video functionality
media/blink/webmediaplayer_impl.{cc,h} - Chromium's main implementation of WebMediaPlayer

How does everything get instantiated?

WebFrameClient::createMediaPlayer() is the Blink embedder API for creating a WebMediaPlayer and passing it back to Blink. Every HTML5 audio/video element will ask the embedder to create a WebMediaPlayer.

For Chromium this is handled in RenderFrameImpl.

GYP/GN Flags

There are a few GYP/GN flags which can alter the behaviour of Chromium's HTML5 audio/video implementation.

ffmpeg_branding
  Overrides which version of FFmpeg to use
  Default: $(branding)
  Values:
    Chrome - includes additional proprietary codecs (MP3, etc..) for use with Google Chrome
    Chromium - builds default set of codecs

proprietary_codecs
  Alters the list of codecs Chromium claims to support, which affects <source> and canPlayType() behaviour
  Default: 0(gyp)/false(gn)
  Values:
    0/false - <source> and canPlayType() assume the default set of codecs
    1/true - <source> and canPlayType() assume they support additional proprietary codecs

LayoutTests
We run the following layout tests:
LayoutTests/media
LayoutTests/http/tests/media

How the %#$& does buffering work?

Chromium uses a combination of range requests and an in-memory sliding window to buffer media. We have a low and high watermark that is used to determine when to purposely stall the HTTP request and when to resume the HTTP request.

It's complicated, so here's a picture:
Subpages (2): Autoplay Media Internals
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