[Bug 730783] bytereader: Improve the performance to find start code for H.264 and H.265

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=730783
  GStreamer | gstreamer (core) | git

--- Comment #13 from Nicolas Dufresne <nicolas.dufresne at collabora.co.uk> 2014-05-30 13:22:33 UTC ---
Some notes, make sure to look at other parsers if you want to fix that. It was
fixed a long time ago in MPEG2 Video, iirc by Mark. Ideally, I'd like the
h264parser library, and other library to have consistent signature.

A second note, would be nice to share your test script, so we can reproduce.
Will make the thing a little more scientific. Also, we have unit tests for this
generic method in tests/check/libs/bytereader.c . I think they could be
improved, but can already catch up if anything isn't completely reliable. You
can run it using:

make -C tests/check libs/bytereader.check

And to debug it:

make -C tests/check libs/bytereader.gdb

I wouldn't create a new bug. This is about improving H264 parsing speed. Why we
push so hard on the other case, is that it will optimize for all architectures
without affecting the readability and maintainability of the code.

We also have bunch or other plan for this mask scan method where we can have
higher gain, https://bugzilla.gnome.org/show_bug.cgi?id=675772

Final notes, thanks for your time and effort looking into this. We really
appreciate that you are taking the time and making this effort in making
GStreamer more efficient. Our review process can be exhausting sometimes, but I
think you can understand that the last thing we'd like is to have code we don't
fully understand, or too much assembly to maintain. So it's important for us to
ask questions, take the time to reproduce, double check there is not error.
Specially in core methods.

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