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

[Michael Niedermayer]

On Sat, May 30, 2009 at 04:22:05PM -0700, Baptiste Coudurier wrote:
> On 5/28/2009 12:25 PM, Baptiste Coudurier wrote:
> > Hi Michael,
> > 
> > On 5/28/2009 4:01 AM, Michael Niedermayer wrote:
> >> 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)
> > 
> > Ok, thanks for clarifying.
> > 
> >>> 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
> > 
> > Ok, let's try to handle this the correct way.
> > If the user seeks to EOF and a new stream (pid) was detected, codec will
> > either be set to the right codec according to the pmt or if unknown
> > codec probing will be called. If EOF is reached we must output packets
> > buffered but it's not reasonable to set codecs to CODEC_ID_PROBE.
> > 
> > So during seek, probe packets should be reset to MAX_PROBE_PACKETS, and
> > eof must set probe_packets to 0.
> > 
> 
> How is it ? :)

too many patches, too many bugs, too little time ...
patience please :)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you really think that XML is the answer, then you definitly missunderstood
the question -- Attila Kinali
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