[FFmpeg-devel] [PATCH] lavf/mov: Add support for edit list parsing.

[Sasi Inguva]

Oops. I messed up with git send-email, and my  message didn't occur in
reply to this thread. So, here I am typing in Gmail..

Hi Clement and Michael,

Sorry that I hadn't started a discussion on the patch before sending it for
review. However this patch has been there for years in our ffmpeg version.
I simply made some cosmetic changes to prepare it to send for review, hence
I haven't wasted much work/time on it. That said, I think that the code we
have, correctly decodes almost 100% of the edit list uploads that we
receive and I think will be of good use to others, at least on a temporary
basis, until a permanent solution can be agreed upon. As can be seen, the
API changes to libav{format/codec/util} are very minor.
I've fixed all the fate tests, and you can find in this doc
https://docs.google.com/document/d/1V2nWYUcKsKv6uycRnknXzAnGjE3mL
YcO_5ti5hLHUn8/pub  , justifications  of existing fate test reference
modifications. I have also separated the patch into 4 patches . I messed up
with git send-email so those patches got sent as separate mails. I am
attaching them as files anyway here.


On Mon, Aug 8, 2016 at 8:09 AM, Clément Bœsch <u at pkh.me> wrote:

> Hi,
>
> On Fri, Aug 05, 2016 at 05:18:39PM -0700, Sasi Inguva wrote:
> > In YouTube we have long been receiving MOV files from users, which have
> non-trivial edit lists (Those edit lists which are not just used to offset
> video start from audio start) and multiple edit lists. Recently the uploads
> of such files has increased with the introduction of apps that allow video
> editing and upload like Vine etc. mov.c in ffmpeg does not have edit list
> parsing support i.e. the support for deciding what video/audio packets
> should be output with what timestamps, based on edit lists. For this
> reason, we had built a basic support for edit list parsing in our version
> of ffmpeg, which fixes the AVIndexEntries built by mov_build_index by
> looking at edit lists, and introduces new DISCARD flags in AVPacket and
> AVFrame to signal to the decoder to discard certain packets.
> >
> > For a while our edit list support was broken, as in it didn't properly
> work for multiple edit lists and it had problems with edit-lists ending on
> B-frames. But we've fixed most of these issues in recent times, and we
> think that now it is in a good enough condition so that it can be submitted
> to HEAD. This will not only help the vast userbase of ffmepg, but will also
> help us with staying up-to-date with ffmpeg and also by adding the power of
> ffmpeg developer community to our MOV support. So here's a go at it.
> > What is supported:
> >  - multiple edit lists
> >  - edit lists ending on B-frames
> >  - zero segment duration edit lists
> >
> > What is not supported:
> >  - Changing the rate of playing with edit lists. We basically ignore
> MediaRate field of edit.
> >
> > I have added fate tests too. Here is a no-sign-in required link to the
> test files https://drive.google.com/folderview?id=0Bz6XfEJZ-
> 9N3R3o3QXNHUGRqbms&usp=sharing.
>
> First, thanks for working on this. But it would be much much more
> appropriate to discuss such changes with developers before engaging
> yourself in such heavy development. As you can guess, this issue has been
> discussed many times in the past within the project, and a proper solution
> had yet to come out of it. It looks like the approach you took was
> dismissed in the past from an infrastructure PoV.
>
> I will have a look to this patch later this week, but please don't follow
> this corporate approach when doing such huge contribution. You're risking
> too much by doing so (your work could be dismissed, or worse your work
> introduce fundamental issues within the project which we'll take years to
> fix because $API)
>
> You can use the mailing list, or simply IRC to have quick talk with us.
>
> --
> Clément B.
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
>
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