[Ffmpeg-devel] Usage of un-initialized variable in function mpeg4_decode_block()
Michael Niedermayer
michaelni
Tue Mar 7 19:55:38 CET 2006
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
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