[FFmpeg-devel] [VA decode] calculation of next marker for MPEG-4 streams
michaelni at gmx.at
Fri Oct 5 19:44:13 CEST 2012
On Fri, Oct 05, 2012 at 08:12:41PM +0530, anuj mittal wrote:
> On Fri, Oct 5, 2012 at 2:28 PM, anuj mittal <am.devel at gmail.com> wrote:
> > Hello
> > I've a MPEG-4 stream that has the code 00 00 within slice data. I see
> > a slight distortion when I try to decode this using HWAccel VAAPI.
> > I've found that the slice size being fed to VA is wrong.
> > 001aca0: 60c8 b7d4 d755 6eb6 66a0 c082 fff8 283a `....Un.f.....(:
> > 001acb0: a7f9 8a7f 8b6d 3c0a 0f2d 9765 b2c6 672a .....m<..-.e..g*
> > 001acc0: 1703 0000 d626 6159 f0c0 3bb4 402f fea0 .....&aY..;.@/..
> > 001acd0: 875f d29f fb00 0001 b65a 5998 0ca7 864e ._.......ZY....N
> > 001ace0: 7393 5739 ce4a 5739 cfa5 c9e0 c9c9 9dce s.W9.JW9........
> > The code in ff_h263_find_resync_marker (ituh263dec.c) in ffmpeg
> > libavcodec returns the position in slice where this code appears and
> > as a result, the slice size being sent to VAAPI is 90B instead of 91E.
> > Commenting this code would get rid of the error.
> > My question is:
> > 1. Would this stream comply with the standard? I tried looking in the
> > standard but didn't find anything related to start code emulation
> > prevention. Does MPEG-4 standard allow start code to be present in the
> > slice data?
> > 2. How should I deal with this?
> > Thank you.
> > Anuj
> I can see that resync_marker is 0 (resync not enabled) for this stream.
> Does it make more sense checking specifically for the length of the
> video packet start code based on vop_coding_type, vop_fcode_forward
> and vop_fcode_backward parameters?
thats required for it to work, i suspect
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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