[FFmpeg-user] ? About ffmpeg's prores implemention

[Paul B Mahol]

On 8/28/20, Phil Rhodes via ffmpeg-user <ffmpeg-user at ffmpeg.org> wrote:
>
> The ProRes implementation is not likely to be perfect in terms of Apple's
> internal spec. They do not publish the spec so we don't know. In general, it
> has been shown to be reasonably reliable when used with most software
> decoders. It has had problems in the past (I haven't checked for years) in
> playback on hardware devices such as Atomos and AJA recorders. It is
> possible to set ffmpeg up to create ProRes-like files that are wildly out of
> spec and are unlikely to play back satisfactorily on anything, but with
> sensible setup it's generally fine. "It's generally fine" is all you're
> getting, sadly. I use it freely in situations where I will have an
> opportunity to fix problems as they occur (they never have) but I would
> hesitate to use it, for instance, for submission of a final master to
> someone.
> In general it's very difficult to figure out exactly when something has
> changed in a particular part of ffmpeg as no change log is published, at
> least nothing which calls out "we have changed something which affects
> prores," but the behaviour of the ProRes implementation has not changed in a

Unlike Apple, everything about ProRes implementation in FFmpeg is open [1].

Your comment that there is not changelog for ProRes in FFmpeg is very unhelpful
and even with unclear intentions.

[1] list of changes:

http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdata.h;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdata.c;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdec.h;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdsp.h;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdsp.c;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresdec2.c;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresenc_anatoliy.c;hb=HEAD
http://git.videolan.org/?p=ffmpeg.git;a=history;f=libavcodec/proresenc_kostya.c;hb=HEAD

> way that's visible to me. Prores is a reasonably simple format, as these
> things go. It's technologically similar to MJPEG or DV.
>
> P
>
>     On Friday, 28 August 2020, 01:01:19 BST, Gary Yost <gary at yostopia.com>
> wrote:
>
>  ’ve got a question about the Prores implementation in ffmpeg because I’ve
> seen some odd behavior here with FCPX (running on a very beefy 16-core Mac
> Pro with 192Gram and an Afterburner card).
>
> When I output files from ffmpeg in ProresLT format and bring them into FCPX,
> they stutter badly… playback is ~5fps.  But when I transcode/optimize them
> in FCPX, which creates Prores422 versions of those files, they play back in
> FCPX seamlessly.
>
> The ffmpeg files _used_ to play back seamlessly on this machine when I was
> doing this Jan-March, but I haven’t been using this workflow since March.
> My questions are:
>
> 1.  Is the Prores implementation in ffmpeg a 100% accurate implementation as
> per the Apple spec?
>
> 2.  Has anything changed in the Prores code transcoding of ffmpeg in the lat
> 4 months?
>
> Thanks!
>
> -g
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