[FFmpeg-devel] [PATCH v2 4/8] ffmpeg: remove sub-frame warning

[Paul B Mahol]

Dana 1. 4. 2016. 15:43 osoba "wm4" <nfxjfg at googlemail.com> napisala je:
>
> On Wed, 23 Mar 2016 22:15:12 +0100
> Michael Niedermayer <michael at niedermayer.cc> wrote:
>
> > On Wed, Mar 23, 2016 at 09:51:46PM +0100, wm4 wrote:
> > > On Wed, 23 Mar 2016 21:36:35 +0100
> > > Michael Niedermayer <michael at niedermayer.cc> wrote:
> > >
> > > > On Wed, Mar 23, 2016 at 08:44:41PM +0100, wm4 wrote:
> > > > > On Wed, 23 Mar 2016 18:37:25 +0100
> > > > > Michael Niedermayer <michael at niedermayer.cc> wrote:
> > > > >
> > > > > > On Wed, Mar 23, 2016 at 06:06:37PM +0100, wm4 wrote:
> > > > > > > On Wed, 23 Mar 2016 17:51:11 +0100
> > > > > > > Michael Niedermayer <michael at niedermayer.cc> wrote:
> > > > > > >
> > > > > > > > On Wed, Mar 23, 2016 at 02:02:11PM +0100, wm4 wrote:
> > > > > > > > > It's not practical to keep this with the new decode API.
> > > > > > > > > ---
> > > > > > > > >  ffmpeg.c | 7 -------
> > > > > > > > >  ffmpeg.h | 1 -
> > > > > > > > >  2 files changed, 8 deletions(-)
> > > > > > > >
> > > > > > > > its not practical in ffmpeg.c but libavcodec should be able
to easily
> > > > > > > > check that a decoder which doesnt declare
AV_CODEC_CAP_SUBFRAMES
> > > > > > > > doesnt decode "subframes"
> > > > > > > > Can you move this check into libavcodec ?
> > > > > > > > i think otherwise nothing would be checking for missing
> > > > > > > > AV_CODEC_CAP_SUBFRAMES anymore
> > > > > > > >
> > > > > > >
> > > > > > > What's the point of this check?
> > > > > >
> > > > > > to keep track of / detect the cases that put multiple decodable
frames
> > > > > > in a packet.
> > > > > >
> > > > > > Whats the point of that?
> > > > > > there where several IIRC
> > > > > > one is that when too many frames are put in a packet
> > > > > > latency increases, another is that seeking granularity is worse
> > > > > > (if its not even one packet for the whole file ...)
> > > > >
> > > > > It's true that too many frames in a packet isn't ideal, but
that's not
> > > > > what the code checks.
> > > > >
> > > > > It checks if an audio decoder not marked with
AV_CODEC_CAP_SUBFRAMES
> > > > > consumes partial packets.
> > > >
> > > > yes, but a check that checks "if a decoder not marked with
> > > > AV_CODEC_CAP_SUBFRAMES consumes partial packets". Is a simple and
> > > > zero overhead way of detecting some (not all) cases where there are
> > > > multiple frames in a packet. One cant look at a sequence of bytes
> > > > that could be any arbitrary format/codec and say
> > > > "thats more than 1 frame" it requires codec specific code,
> > > > the decoders already do what is needed for some cases, for the
others
> > > > there is (please correct me if iam wrong which might be) no easy
> > > > way except maybe running the parser if one exists over it but that
> > > > would not be zero overhead
> > > >
> > > >
> > > > > That might be useful as debug check in
> > > > > libavcodec or so, or by properly reviewing patches for new
decoders.
> > > >
> > > > Iam not sure if i understand what you mean exactly but this somehow
> > > > sounds like an implication that people would not review patches
> > > > properly.
> > > > Thats a serious accusation if thats what was meant. Either there is
> > > > a problem then it should be pointed to very specifically so it can
be
> > > > solved or such implications shouldnt be made at all.
> > >
> > > Well, I'm not sure what else this check is useful for. A new audio
> > > decoder will need explicit code to handle multiframe audio by
returning
> > > the exact number of bytes parsed, instead of e.g.
> > > "return avpkt->size;". So it should be pretty obvious whether a
decoder
> > > does this?
> >
> > yes, though there may be corner cases where it has to do that
> > and it might be more robust.
> >
> >
> >
> > >
> > > Anyway, I could move this check to avcodec_decode_audio4(), would that
> > > be ok?
> >
> > yes and thanks!
> >
>
> So I actually tried this, and it turns out at least shorten (and maybe
> many more codecs) raises this warning, because it doesn't set
> AV_CODEC_CAP_SUBFRAMES. And nobody ever cared.
>
> Give me a reason why I should, instead of sending a patch to deprecate
> AV_CODEC_CAP_SUBFRAMES?

It should set it because it is not sane format.

> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel