Ted is touching some of this code currently, so seems like a good followup task.

If we want to handle videos with inline text tracks, we would need this? I think we may want to make use of this in the future.

Can you elaborate on why you think we'd want to support this? WebVTT has long been the accepted solution here instead. It's been there for 5+ years unused.

It depends if I understand correctly what this feature is doing. If it's about handling inline text tracks, I believe we would want this to be able to read video files with inline text tracks which may become a use case with Chrome dealing more with local media files.

Do you know of any sites using media with embedded WebVTT subtitles? IIRC while allowed in mp4/webm, I haven't ever seen it used beyond tech demos. HLS/DASH store it as a separate file. So I think anything we do for downloaded media would need to do what Chromecast is doing and handle subtitles alongside the file in JS from WebVTT.

fyi - https://www.telecineplay.com.br/ use embedded WEBVTT subtitles and are currently frustrated that Chrome 66 is not showing them for their users. (https://github.com/Dash-Industry-Forum/dash.js/issues/2564)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/13fb19bf2d3cf3caa031cdd0ecaa3214e043cb2d

commit 13fb19bf2d3cf3caa031cdd0ecaa3214e043cb2d
Author: Ted Meyer <tmathmeyer@chromium.org>
Date: Wed May 23 22:07:11 2018

Split the layout test for remove-track

Keep separate tests for in-band and out-of-band text tracks.

Bug: 826419
Change-Id: I2e888d47ddda080bbc7b6cd6f1f645d064c5a6fa
Reviewed-on: https://chromium-review.googlesource.com/1070570
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561269}
[modify] https://crrev.com/13fb19bf2d3cf3caa031cdd0ecaa3214e043cb2d/third_party/WebKit/LayoutTests/external/WPT_BASE_MANIFEST.json
[add] https://crrev.com/13fb19bf2d3cf3caa031cdd0ecaa3214e043cb2d/third_party/WebKit/LayoutTests/external/wpt/html/semantics/embedded-content/media-elements/track/track-element/track-remove-track-inband.html
[modify] https://crrev.com/13fb19bf2d3cf3caa031cdd0ecaa3214e043cb2d/third_party/WebKit/LayoutTests/external/wpt/html/semantics/embedded-content/media-elements/track/track-element/track-remove-track.html

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4ca53dec2e2711a6861d52f12b06b42abaea48f4

commit 4ca53dec2e2711a6861d52f12b06b42abaea48f4
Author: Ted Meyer <tmathmeyer@chromium.org>
Date: Sat May 26 00:21:31 2018

Remove support for inline text tracks

inline text tracks are currently hidden behind a feature flag and is
almost completely unused, so this CL removes the flag as well as all
behavior that would be enabled by its use.

Bug: 826419
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ide06bcde063ec57898e3129c28550929fa4104ea
Reviewed-on: https://chromium-review.googlesource.com/1058930
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562080}
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/chromecast/media/cma/test/frame_segmenter_for_test.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/content/browser/renderer_host/render_process_host_impl.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/content/shell/app/shell_main_delegate.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/demuxer.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/media_switches.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/media_switches.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/media_url_demuxer.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/media_url_demuxer.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/media_url_demuxer_unittest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/mock_demuxer_host.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/mock_filters.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/pipeline_impl.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/pipeline_impl.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/base/pipeline_impl_unittest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/cast/sender/h264_vt_encoder_unittest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/chunk_demuxer.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/chunk_demuxer.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/chunk_demuxer_unittest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/demuxer_perftest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/ffmpeg_demuxer.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/ffmpeg_demuxer.h
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/filters/ffmpeg_demuxer_unittest.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/test/pipeline_integration_test.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/media/test/run_all_unittests.cc
[modify] https://crrev.com/4ca53dec2e2711a6861d52f12b06b42abaea48f4/third_party/WebKit/LayoutTests/TestExpectations

Note, this issue makes  bug 645327  obsolete.

Not yet complete:
See https://chromium-review.googlesource.com/c/chromium/src/+/1316412#message-89cd8ea7d6ef6d27f2d4839165140172d5b2488c