xhwang@/dalecurtis@/hbengali@ please help triage this. Thanks!
(I'll continue to focus my current work on the FLAC MSE-in-mp4  bug 666000 .)

There's no easy way to query this from the renderer, so for now I'd just mark this as unsupported. I.e. return false for EME+flac on Android in mime_util_internal. Ideally by updating the PlatformInfo struct with this new variable.

Chatting with xhwang@, and looking at https://codereview.chromium.org/2866473004/ (and the current cdm message filter: https://cs.chromium.org/chromium/src/components/cdm/browser/cdm_message_filter_android.cc?q=cdm_message_filter_android.cc&sq=package:chromium&dr&l=57) indicates that flac-in-mp4 on android is already disabled. Unfortunately, encrypted_media_supported_types_browsertest is disabled for Android, so none of this is auto-tested. In my CL adding unencrypted '{audio,video}/mp4; codecs="flac"' canPlayType support as prereq for fixing  bug 666000 , I'll include a comment similar to the vorbis comment already in https://cs.chromium.org/chromium/src/components/cdm/browser/cdm_message_filter_android.cc?q=cdm_message_filter_android.cc&sq=package:chromium&dr&l=57.

Perhaps some refactoring to make it clear precisely where the determination of mime/key system/codec support per platform is done would help, too, but is out of scope of my MSE work in  bug 666000 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726

commit b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726
Author: Matt Wolenetz <wolenetz@chromium.org>
Date: Fri Jul 21 18:00:35 2017

Enable src= support for FLAC-in-MP4

Since M56, all Chrome build types that include proprietary codecs and
use the unified media pipeline have been able to demux and decode
FLAC-in-MP4, but canPlayType() hasn't been updated yet.

Further motivation to update that, a prerequisite for supporting
FLAC-in-MP4 with MSE in Chrome is that canPlayType('{audio,video}/mp4,
"flac"') needs to return "probably".

This change updates canPlayType() to indicate FLAC-in-MP4 is supported,
and includes new tests for src= FLAC-in-MP4.

A further complication is that MP4's AudioSampleEntry samplerate field
is fixed point 16.16 bits, so lacks range to handle bitrates above
65535Hz. The FLAC-in-MP4 spec [1] guides how to encode the correct
sample rate when it is outside this scale, and this change includes test
files at both 44.1kHz and 192kHz to verify FFmpegDemuxer extracts the
correct samplerate information.

Also, based on investigation leading to https://crbug.com/747050#c3,
this change includes a comment indicating lack of decode support for
*encrypted* FLAC (in any container) on Android (which would need FLAC
decode support directly in MediaCodec, rather than in MediaExtractor as
some devices appear to do). In the future, perhaps more refined logic
can be used to identify cases where encrypted FLAC-in-MP4 on Android is
supported by the device.

BUG= 666000 ,747050
TEST=Added sfx-flac.mp4 FFmpeg AudioDecoderTest cases, basic media
playback browsertests for bear-flac.mp4 and bear-flac-192kHz.mp4,
FFmpegDemuxerTests, PipelineIntegrationPerfTests, and a
PipelineIntegrationTest; Updated MediaCanPlayTypeTests and
MimeUtilTest.ParseAudioCodecString;

Change-Id: I04df11c34aa539c53dd2c8868257f7ef9608ddc7
Reviewed-on: https://chromium-review.googlesource.com/580575
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Matthew Wolenetz <wolenetz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488703}
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/components/cdm/browser/cdm_message_filter_android.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/content/browser/media/media_browsertest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/content/browser/media/media_canplaytype_browsertest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/base/mime_util_internal.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/base/mime_util_unittest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/filters/audio_decoder_unittest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/filters/ffmpeg_demuxer_unittest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/data/README
[add] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/data/bear-flac-192kHz.mp4
[add] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/data/bear-flac.mp4
[add] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/data/sfx-flac.mp4
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/pipeline_integration_perftest.cc
[modify] https://crrev.com/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/media/test/pipeline_integration_test.cc

matt, since you have a CL for this bug, I assigned it to you.

w.r.t. this bug, that CL in #4 just added a comment pointing to this bug: https://chromium.googlesource.com/chromium/src/+/b6be2ef08a6cc5ae86dcc4a9cd2b3e3066353726/components/cdm/browser/cdm_message_filter_android.cc#58

=> xhwang@ (EME) for getting this support updated eventually (depends most likely on Android). Clear (non-EME) MSE and src= FLAC decode on Android is done with FFmpeg.

Xiaohan, send it back my way if you need :)

EME only supports WebM and MP4 (https://w3c.github.io/encrypted-media/format-registry/stream/#registry). I don't know if the FLAC container has mechanisms to signal encryption, which would be required to support "audio/flac" in EME.

Android DRM requires platform support for all codecs. It doesn't have to be a ".secure" codec, but it does need to be decoded in the OS.

@#7, to be clearer, I've landed ( bug 666000 ) MSE support for demux + decode/playback of FLAC-in-ISOBMFF(MP4). I filed this bug when I discovered that our Android pipeline (with the unified pipeline and ffmpeg FLAC decode) should work fine for FLAC-in-ISOBMFF in MSE), but that our EME pipeline's usage of MediaCodec + MediaDrm on Android would necessitate support for FLAC (codec, not container) decode in MediaCodec, which is not-uniformly supported. I wasn't promoting that .flac container needs EME support in Chrome (any platform, including Android).

For audio, we don't need a secure decoder. So on Android versions/devices where FLAC codec is supported, we should be able to support EME+Flac (in theory). That being said, given there's no interest in encrpted FLAC, I'll probably just mark this as WontFix. We can reopen this issue if that assumption changes.