[webkit-gtk] Question about Media Source Extension

Konstantin Tokarev annulen at yandex.ru
Wed Feb 28 03:18:40 PST 2018

28.02.2018, 12:45, "Enrique Ocaña González" <eocanha at igalia.com>:
> El miércoles, 28 de febrero de 2018 8:20:12 (CET) Cédric Bellegarde escribió:
>>  I recently add a personnal build server for ArchLinux to get debug
>>  symbols packages for GNOME stack.
>>  enable-mediasource was True in Eolie, first test: 1080p is available in
>>  Youtube but WebKitGTK crashes.
>>  So, I decide to force enable-mediasource to False in Eolie for now
>>  instead of rebuilding WebKitGTK.
>>  And here my surprise, with -DENABLE_MEDIA_SOURCE=ON and
>>  enable-mediasource=False, 1080p is available in YouTube and WebKitGTK
>>  does not crash anymore.
>>  Why this behaviour?
> MSE on WebKitGTK+ is a work-in-progress feature. While it works reasonably
> well for https://youtube.com/tv (note that this isn't the regular youtube.com
> website!) with MP4 using H.264 and mpeg audio codecs, it's still work in
> progress regarding the support of webm using vp9 and opus codecs. Also, the
> current work depends on GStreamer patches that are still on their way to get
> merged upstream, so things won't work well in unpatched vanilla distros. Your
> mileage may vary depending on the GStreamer multimedia codecs present on your
> system (eg: It looks like Fedora doesn't ship H.264 codecs and our webm
> implementation is still unstable).
> When you "enable-mediasource=False", the browser stops advertising to the
> webpage that it supports MSE. Therefore, the webpage tries to use the regular
> non-MSE video player and a different codepath is exercised in WebKit.
>>  Why not enabling MEDIA_SOURCE in WebKitGTK if it works with
>>  enable-mediasource=False?
> The build flag is disabled in order to avoid bloating the binary with MSE code
> (because of the MEDIA_SOURCE build flag) that in the end shouldn't (because
> it's still work in progress) and wouldn't (because of enable-
> mediasource=False) be used by stable distros out there.

This implies that WebKitGTK's users are distros, and not application developers
and their end-users (who may want enable MSE for content which is known to work)

> If you know what features your system supports and want to play with MSE at
> your own risk, enable the flags yourself.
> Now about the specific crash you're having, we would appreciate a bug report
> in https://bugs.webkit.org with the "[MSE][GStreamer]" tags in the bug title.
> If you can provide a backtrace of the crash and GStreamer log and pipeline
> dumps, it would help us a lot to find the root cause.
> To get GStreamer logs and pipeline dumps, define these environment variables
> in your shell before manually launching the browser:
> export GST_DEBUG_DUMP_DOT_DIR=/tmp
> export
> GST_DEBUG="*:WARN,webkitmediaplayer:TRACE,webkitmse:TRACE,webkitmediasrc:DEBUG"
> Then collect all the *.dot files left in your /tmp directory.
> Thank you.
> --
> Enrique Ocaña González
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