[FFmpeg-devel] [RFC][PATCH] return packets for known codecs earlier when codec probing is done

Michael Niedermayer michaelni
Thu May 28 02:48:48 CEST 2009


On Wed, May 27, 2009 at 05:47:22PM -0700, Baptiste Coudurier wrote:
> On 5/27/2009 5:10 PM, Michael Niedermayer wrote:
> > On Wed, May 27, 2009 at 04:40:49PM -0700, Baptiste Coudurier wrote:
> >> On 5/27/2009 3:00 PM, Michael Niedermayer wrote:
> >>> On Wed, May 27, 2009 at 12:54:27AM -0700, Baptiste Coudurier wrote:
> >>>> Hi Michael,
> >>>>
> >>>> Michael Niedermayer wrote:
> >>>>> [...]
> >>>>>
> >>>>>> @@ -537,10 +537,18 @@ int av_read_packet(AVFormatContext *s, AVPacket *p
> >>>>>>  
> >>>>>>          av_init_packet(pkt);
> >>>>>>          ret= s->iformat->read_packet(s, pkt);
> >>>>>> -        if (ret < 0)
> >>>>>> -            return ret;
> >>>>>> +        if (ret < 0) {
> >>>>>> +            if (!pktl)
> >>>>>> +                return ret;
> >>>>>> +            for (i = 0; i < s->nb_streams; i++)
> >>>>>> +                if (s->streams[i]->codec->codec_id == CODEC_ID_PROBE)
> >>>>>> +                    s->streams[i]->codec->codec_id = CODEC_ID_NONE;
> >>>>>> +            continue;
> >>>>>> +        }
> >>>>> i dont like this
> >>>>>
> >>>> Well, we have a problem if probe_packets is not 0 when eof is reached.
> >>>> Do you see another way to avoid this ?
> >>> is this special case really relevant?
> >>> it just looses data on streams when all of the following is true
> >>> * stream is set to CODEC_ID_PROBE
> >>> * stream contains less than 100 packets in the whole file
> >>> * probing fails even with all packets in the whole file
> >> I think it is:
> >> code will call av_read_packet until st->probe_packets is 0, which will
> >> provoke an infinite loop.
> > 
> > hmm, i must be missing something, as i thought the packets would just never
> > be output and the player would end at EOF in whichever way it did before the
> > patch
> 
> Before the patch, ie currently, if EOF is reach, packets are not outputed.
> This is a bug IMHO.

i agree its a bug, the patch without the controversal part would reduce it
to the case where less than 100 packets are in a whole file && probing
fails.
Your suggested fix, fixes it but introduces a new bug, namely that seeking
to EOF causes probing to fail for all streams permanently, even if the
user seeked back afterwards. That is what concerns me besides that i had
a bad feeling about that part of the patch.
I wish i knew a solution, but i dont ATM


[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The bravest are surely those who have the clearest vision
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notwithstanding go out to meet it. -- Thucydides
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