[Ffmpeg-devel] problem decoding frames when first frame is B

[Michel Bardiaux]

rkmr.em at gmail.com wrote:
> On 4/20/07, M?ns Rullg?rd <mans at mansr.com> wrote:
>>
>> "rkmr.em at gmail.com" <rkmr.em at gmail.com> writes:
>> > I have a valid MPEG-2 video stream in which the first two frames are
>> > B-frames. ffmpeg is not able to decode those two frames:
>> >
>> >                        avcodec_decode_video( m_vDec, m_decodedPicture,
>> > &got_picture, (uint8_t*) samplePtr, sampleLength );
>> >
>> > got_picture is 0 for the first two frames. Is this a know problem?
>>
>> Upload a sample, please.
> 
> 
> can you tell how to do this? it is a 49MB file.
> 
> 
> Do you mean that the first frame is a B-frame with only intra coded
>> blocks, or that the first frames in display order are B-frames
>> predicted against a following (display order) I-frame, which is the
>> first coded frame?
> 
> 
> the display order is like this:
> BBIBBP..
> I am not sure how it is actually coded.

I have seen MPEG (1, not 2) streams coming from hardware encoders and 
having that structure. The full GOP structure was

BBIBBPBBPBBP|BBIBBPBBPBBP|...

the 2 leading B-frames being coded against the last P-frame of the 
preceding GOP. A typical not-closed GOP. And a nightmare to decode.

-- 
Michel Bardiaux
R&D Director
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