Description
This feature is part of the Device Capabilities APIs defined in W3C document.
It provides web runtime applications with the ability to get the supported
audio/video codecs' information(*) on the client machine(Android device). Take
an example as the user case, with this information, the server can provide the
most appropriate encoding format of audio/video stream if possible.
(*) The required information:
Audio Video
format (DOMString) YES YES
hwAccel (Boolean) N/A YES
encode (Boolean) N/A YES
Spec
http://w3c.org/2012/sysapps/device-capabilities/
Affected component
java API:
runtime/android/java/src/org/xwalk/runtime/extension/api/device_capabilities
js API: sysapps/device_capabilities
test case: test/android/data
Related feature in Jira
https://crosswalk-project.org/jira/browse/XWALK-48/
Target Release
Crosswalk-M3
Target Platform
Android
Implementation details
1) On Android version >= 4.1(API level >= 16):
The implementation uses the 'MediaCodec' APIs which is available since Android
4.1(API level 16) to get the codec list. Through this API, we can get the codec
list stored in ROOTDIR_OF_ANDROID/system/etc/media_codec.xml to satisfy the
requirements in spec.
2) On Android 4.0(API level 15):
Android 4.0 does not offer 'MediaCodec' API, as well as file
ROOTDIR_OF_ANDROID/system/etc/media_codec.xml file in its system. So we need
offer a fallback solution for 4.0. The solution is offer an 'MediaCodec'
compatible API, this API will return the hard coded codec lists. The original
list comes from media_codec.xml on 4.1.
3) Parse the name string
In Android 4.x, all codecs are based on the OpenMAX IL framework, and the
format name we get from the system are always wrapped in many other strings,
such as 'OMX.google.h263.decoder'. As a result, we need to parse it out. Our
method is maintaining a constant list of the codec names(According to:
http://www.chromium.org/audio-video and
https://developer.mozilla.org/en-US/docs/HTML/Supported_media_formats) and
parse each name(such as h263) out according to the list.
3) Current problem:
Besides the hardcode on 4.0, we cannot get the hardware acceleration status
either. By either using current Android API(up to 4.2) or parsing files,
there's no way to figure out whether a codec is hardware-accelerated based on
current Android system, so this value is set to 'false' by default now.
Regards,
Yiran & Yuanhang
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