[Ffmpeg-devel] H264 segfault

leon jorgunsen leon.jorgunsen
Sat Jun 4 00:51:21 CEST 2005

> De: M?ns Rullg?rd <mru at inprovide.com>
> A: FFMpeg development discussions and patches <ffmpeg-devel at mplayerhq.hu>
> Objet: Re: [Ffmpeg-devel] H264 segfault
> Date: Fri, 03 Jun 2005 17:51:32 +0200

> "leon jorgunsen" <leon.jorgunsen at caramail.com> writes:
> >> On Fri, Jun 03, 2005, M?ns Rullg?rd wrote:
> >> > Derk-Jan Hartman <d.hartman at student.utwente.nl> writes:
> >> > That clip doesn't contain any IDR frames, so it won't be playable.
> >>  Wrong. AVC broadcast streams do not use IDR frames (or very few) to
> >> be able to do open gop.
> >>  You need to start decoding from I frame (there is a SEI message to
> >> tell you which one can be used)
> >
> > Recovery point SEI messages may be used by Broadcasters.
> > But the stream contains IDR and no SEI NAL units.
> Show me.

The first NAL units of the H.264 stream are "Access unit delimiter" 
or "Coded slice of a non-IDR picture", so you cannot decode it as 
no PPS/SPS can be activated.
After those "not-decodable" NAL units, a SPS and a PPS NAL units 
arrive just before a "Coded slice of an IDR picture" NAL unit.
The pps_id present in the slice headers allows a decoder to 
activate the SPS and PPS already received. 
So you can decode the video stream properly from this point.
The SPS ans PPS are repeated before every other IDR in the stream
and no SEI is present.

-- Leonjo

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