[FFmpeg-devel] RTP mark bit not passed to parse_packet

[Alexandre FERRIEUX - FT/RD/SIRP/ASF/SOFTL]

Michael Niedermayer wrote:
> On Thu, Jan 15, 2009 at 06:53:45PM +0100, Alexandre FERRIEUX - FT/RD/SIRP/ASF/SOFTL wrote:
>> Michael Niedermayer wrote:
>>>>>> However, I'm still struggling to understand why the command:
>>>>>> doesn't even create "out.263" nor prints any of the hex dumps...
>>>>> a few printf()/av_log() should tell you where it gets stuck an why
>>>> See my answer to Luca: we never get past av_find_stream_info, never 
>>>> calling my code. Please answer there.
>>> the thing is ffplay/ffmpeg file.h263 has to get past it if it plays the file,
>>> what is different?
>>> A few printf/av_log in av_find_stream_info() should show what is different ...
>> Indeed, thanks !
>>
>> Further investigation (printing the incremented counter of frames in 
>> av_find_stream_info()) shows that it takes a fairly large number of 
>> frames to decide, unless an EOF occurs I guess. But in RTP/UDP there's 
>> no EOF of course, and I was repeatedly streaming the same short 
>> sequence, so when the seqnum/timestamps had a discontinuity, maybe the 
>> guessing work was reset...
>>
>> Anyway, streaming a longer sequence works.
>>
>> A few ancillary questions:
>>
>> 1) This means all those frames are accumulated in memory, right ?
> 
> yes
> 
> 
>> 2) What extra info could I have provided (eithr in the SDP or in 
>> command-line options) so that this guessing work be avoided ?
> 
>         for(i=0;i<ic->nb_streams;i++) {
>             st = ic->streams[i];
>             if (!has_codec_parameters(st->codec))
>                 break;
>             /* variable fps and no guess at the real fps */
>             if(   tb_unreliable(st->codec)
>                && duration_count[i]<20 && st->codec->codec_type == CODEC_TYPE_VIDEO)
>                 break;
>             if(st->parser && st->parser->parser->split && !st->codec->extradata)
>                 break;
>             if(st->first_dts == AV_NOPTS_VALUE)
>                 break;
>         }
>         if (i == ic->nb_streams) {
>             /* NOTE: if the format has no header, then we need to read
>                some packets to get most of the streams, so we cannot
>                stop here */
>             if (!(ic->ctx_flags & AVFMTCTX_NOHEADER)) {
>                 /* if we found the info for all the codecs, we can stop */
>                 ret = count;
>                 break;      <------------------------------------
>             }
>         }
> 
> it should leave av_find_stream_info() at the marked point
> add a few printf/av_log() to find out why this is not reached

Thanks. What happens here is that has_codec_parameters() returns FALSE 
for the video codec (H263). Stepping into it shows that:

     case CODEC_TYPE_VIDEO:
         val = enc->width && enc->pix_fmt != PIX_FMT_NONE;

here *both* conditions in the && are false :)

So I guess I have my answer: I should provide externally (1) a nonzero 
width and (2) a non-NONE pix_fmt. (what's the easiest way of providing 
them ? command-line options or SDP ?)

May I ask *why*, out of the zillions of parameters, just these two are 
needed, and justify swallowing 91 frames (not just 1) ?

-Alex