[FFmpeg-devel] [PATCH] mpeg12dec: don't assert on unknown chroma format

[Michael Niedermayer]

On Wed, Sep 30, 2015 at 02:29:43PM +0200, Hendrik Leppkes wrote:
> On Wed, Sep 30, 2015 at 2:10 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Wed, Sep 30, 2015 at 12:42:59PM +0200, Hendrik Leppkes wrote:
> >> The chroma format can be still unset in postinit when a badly cut stream
> >> starts with a slice instead of a sequence header. This is a common
> >> occurance when feeding avcodec from a Live TV stream.
> >> ---
> >>  libavcodec/mpeg12dec.c | 1 -
> >>  1 file changed, 1 deletion(-)
> >>
> >> diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
> >> index 5d916d1..b3c2c45 100644
> >> --- a/libavcodec/mpeg12dec.c
> >> +++ b/libavcodec/mpeg12dec.c
> >> @@ -1389,7 +1389,6 @@ static int mpeg_decode_postinit(AVCodecContext *avctx)
> >>              case 1: avctx->chroma_sample_location = AVCHROMA_LOC_LEFT; break;
> >>              case 2:
> >>              case 3: avctx->chroma_sample_location = AVCHROMA_LOC_TOPLEFT; break;
> >> -            default: av_assert0(0);
> >>              }
> >>          } // MPEG-2
> >
> > This assert double checks that the context init which uses
> > width/height/chroma format is done after the chroma format and w/h has
> > been read from the headers
> > if this is reached without the headers being read then the code is
> > buggy and removing the assert will not fix that bug
> >
> > also if there is no sequence header how is width/height set ?
> > theres a check for width/height before mpeg_decode_postinit is called
> >
> 
> The dimensions are set by the caller in the avctx before opening the
> codec, which apparently inits the mpeg context as well.
> 
> Feel free to fix it differently, error out or something, but I can
> trip an assert with input data, which should never happen.

how can this be reproduced ?

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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