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

Michael Niedermayer michaelni
Thu May 28 13:01:46 CEST 2009


On Wed, May 27, 2009 at 06:12:37PM -0700, Baptiste Coudurier wrote:
> On 5/27/2009 5:48 PM, Michael Niedermayer wrote:
> > 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. 
> 
> Well, probing should be executed by av_find_stream_info basically, and
> seeking should not occur during this process.

thats the ideal world case, yes but with mpeg-ts streams can start later
if iam not mistaken (like 2 movies which each happen to use different 
codecs or have subtitles in more or less languages)


> 
> But I don't really get what you mean by seeking to EOF and probing.
> Why would an user seek to EOF ?

because he clicked the wrong button ;)
users are silly, but ffmpeg should still not misbehave, especially not in
such a obscure way, i mean a mistaken seek to EOF shortly after a transition
between 2movies could lead to missing audio, maybe its a 1 in 100000 chance
or even less likely but its a bug from the users point of view

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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