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

[Hendrik Leppkes]

On Wed, Sep 30, 2015 at 2:33 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> 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 ?
>

I can only trigger it with API usage, not through the CLI tools, so I
cannot produce a test case.
Just replace the assert with a error return, that should cover everything.

- Hendrik