[FFmpeg-devel] Corrupted blocks and seeking issues in H264 disc sources

Michael Niedermayer michaelni
Wed Jul 18 02:36:16 CEST 2007


On Sat, Jul 14, 2007 at 10:22:58AM +0200, Andreas ?man wrote:
> Hello,
> infernix wrote:
> > Hi,
> > 
> > Andreas, perhaps this new sample can give you more insight as to what 
> > the problem is? If I find more blocks, I'll upload them and post a followup.
> > 
> I've taken a quick look at it, and it seems the motion vectors
> are somehow incorrect for the affected macro blocks. see [1]
> and [2]. (Both frames have errors in the bottom left part of
> the picture)

issue4 also has an error at the top right part of the same image which
has that black block

> I've done some additional tracing on [1]:
> [h264 @ 0x84b1de8]pic:11 mb:15/58
> [h264 @ 0x84b1de8]mb_type = 0x1008, partition_count = 1, cbp = 0x0
> [h264 @ 0x84b1de8]pred_motion match_count=3
> [h264 @ 0x84b1de8]pred_motion ( 0  0 -2) ( 0  0  0) ( 0  8 -8) -> ( 0  0 
> -2) at 15 58 0 list 0
> [h264 @ 0x84b1de8]final mv:198 102, cabac delta: 198 104
> It would seem that the output from decode_cabac_mb_mvd() is
> incorrect, but why (or if) it fails for this particular macroblock,
> i'm not expert enough to tell.

are you sure its decode_cabac_mb_mvd() ? i would rather guess that the issue
is from a wrongly predicted mv  (which can be caused
by less vissible errors in previous frames if the buggy frame is a b frame) or
wrong reference image
an error in decode_cabac_mb_mvd() is likely to cause more bitstream errors
after that but there dont seem to be any ...

also you could compare the various values with what the reference
implementation produces (this is easy as the reference implementation
can just dump all that for your viewing pleasure)

and doing a bytewise compare between the decoded pictures of the reference
impl and ffmpeg should also help alot, both MUST be absolutely identical

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I do not agree with what you have to say, but I'll defend to the death your
right to say it. -- Voltaire
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