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

[Hendrik Leppkes]

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.

-  Hendrik