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

Måns Rullgård mans
Mon Apr 23 23:45:01 CEST 2007

"rkmr.em at gmail.com" <rkmr.em at gmail.com> writes:

> On 4/23/07, Mathieu Monnier <manao at melix.net> wrote:
>> >>>>> Open GOP makes some sense when
>> >>>>> random access is impossible, such as broadcast, which is where it
>> >>>>> is primarily found.  DVD uses closed
>> Open gop always make sense.
>> >>> So it is not possible to decode the first two frames?  Is this true
>> >>> even with the latest svn version of ffmpeg?
>> It can't be decoded if the broken link flag is set to 1 in the gop
>> header. I wouldn't trust a broken link flag anyway, and I would bet
>> anyway that they aren't decodable
>> >> The first frame produced when the decoder is switched on must be
>> >> possible to decode somehow.  If you jump into the stream at a later
>> >> point you'll always have a couple of initial B-frames with one
>> >> reference before your starting point.  Not even FFmpeg can invent this
>> >> missing data.  The decoder copes with it just fine though, so there's
>> >> no big deal.
>> I think it rather seek to the following intra.
>> > I am building a frame accurate video decoder using ffmpeg and I
>> > need to be able to decode those frames.
>> I don't think you can.
> Do you know how hardware decoders would deal this issue?

They skip the frames that can't be decoded.  There is no other way.

M?ns Rullg?rd
mans at mansr.com

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