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

[rkmr.em at gmail.com]

On 4/23/07, Michel Bardiaux <mbardiaux at mediaxim.be> wrote:
>
> M?ns Rullg?rd wrote:
> > Michel Bardiaux wrote:
> >> 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|...


This is exactly the frame strucuture and is a hardware encoder that is
producing this stream!!


>> 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.
> >
> > The only problem is that you don't have the reference frame for the
> first
> > couple of frames.  Nothing to worry about once you've got the first two
> > non-B frames.  Open GOP makes some sense when random access is
> impossible,
> > such as broadcast, which is where it is primarily found.  DVD uses
> closed


So it is not possible to decode the first two frames?  Is this true even
with the latest svn version of ffmpeg?
thanks a lot!
mark