[Ffmpeg-devel] Usage of un-initialized variable in function mpeg4_decode_block()

[Michael Niedermayer]

Hi

On Tue, Mar 07, 2006 at 03:11:42PM +0000, Rahul Kumar wrote:
> Hi everyone,
> 
> I have been trying to test the ffmpeg code against ISO bitstreams (&
> the ISO decoder). I found failure for one of the MPEG4 Simple Profile
> bitstreams due to the following code:
> 
> FILE NAME: h263.c
> 
> mpeg4_decode_block()
> {
>     if(intra)
>     {
>       if(s->qscale < s->intra_dc_threshold)
>       {
>         // initialize dc level & dc_pred_dir
>       }
>       else
>       {
>         //set i = -1 without initializing dc_pred_dir
>       }
> ...
> ...
> ..//further down in the code
>         if (s->ac_pred) {
>             if (dc_pred_dir == 0)
>                 scan_table = s->intra_v_scantable.permutated; /* left */
>             else
>                 scan_table = s->intra_h_scantable.permutated; /* top */
>         } else {
>             scan_table = s->intra_scantable.permutated;
>         }
> 
> 
> Note that if ((s->qscale < s->intra_dc_threshold) && (s->ac_pred==1)),
> then the above code will use dc_pred_dir without initializing it. This
> can be sorted by putting a small code to initialize the dc_pred_dir in
> the first else condition.

could you provide a video which needs this change so we can confirm that
the new code actually works
and could you post a patch as described at 
http://ffmpeg.sourceforge.net/ffmpeg-doc.html#SEC36

[...]
-- 
Michael