[FFmpeg-devel] [PATCH] Fix decoding crash on some trashed interlaced MPEG2 streams. This fixes issue 2367.

[Måns Rullgård]

Anatoly Nenashev <anatoly.nenashev at ovsoft.ru> writes:

> On 18.02.2011 03:47, M?ns Rullg?rd wrote:
>> Anatoly Nenashev<anatoly.nenashev at ovsoft.ru>  writes:
>>
>>    
>>>  From 20e1e656ab07edbfaec5e329a408139720c6b8e7 Mon Sep 17 00:00:00 2001
>>> From: anatoly<anatoly.nenashev at ovsoft.ru>
>>> Date: Fri, 18 Feb 2011 01:01:45 +0300
>>> Subject: [PATCH] Fix decoding crash on some trashed interlaced MPEG2 streams. This fixes issue 2367.
>>>
>>> ---
>>>   libavcodec/mpeg12.c |    5 +++++
>>>   1 files changed, 5 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
>>> index 3c73627..28292ab 100644
>>> --- a/libavcodec/mpeg12.c
>>> +++ b/libavcodec/mpeg12.c
>>> @@ -1763,7 +1763,12 @@ static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
>>>           s->dest[1] +=(16>>  lowres)>>  s->chroma_x_shift;
>>>           s->dest[2] +=(16>>  lowres)>>  s->chroma_x_shift;
>>>
>>> +        if (s->mb_intra || !field_pic || s->last_picture.data[0] ||
>>> +            s->first_field || s->picture_structure != s->field_select[0][0] + 1) {
>>>      
>> Is it really necessary to do all these checks per MB?
>>    
>>
>
> You are right. Checks for "field_pic", "s->last_picture.data[0]",
> "s->first_field" can be done outside the loop. Changed patch in
> attachment.
>
>
> From ecdb1bfe09823bf423a86e6866b129e5bcabf14f Mon Sep 17 00:00:00 2001
> From: anatoly <anatoly.nenashev at ovsoft.ru>
> Date: Fri, 18 Feb 2011 12:08:05 +0300
> Subject: [PATCH] Fix crash of decoder on MPEG2 interlaced streams (issue 2367)
>
> ---
>  libavcodec/mpeg12.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
> index 3c73627..45c1881 100644
> --- a/libavcodec/mpeg12.c
> +++ b/libavcodec/mpeg12.c
> @@ -1640,6 +1640,8 @@ static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
>      AVCodecContext *avctx= s->avctx;
>      const int field_pic= s->picture_structure != PICT_FRAME;
>      const int lowres= s->avctx->lowres;
> +    const int check_mb_inter = field_pic && !s->first_field &&
> +        s->pict_type == FF_P_TYPE && !s->last_picture.data[0];
>
>      s->resync_mb_x=
>      s->resync_mb_y= -1;
> @@ -1763,7 +1765,12 @@ static int mpeg_decode_slice(Mpeg1Context *s1, int mb_y,
>          s->dest[1] +=(16 >> lowres) >> s->chroma_x_shift;
>          s->dest[2] +=(16 >> lowres) >> s->chroma_x_shift;
>
> +        if (!check_mb_inter || s->mb_intra ||
> +            s->picture_structure != s->field_select[0][0] + 1) {
>          MPV_decode_mb(s, s->block);
> +        } else {
> +            av_log(avctx, AV_LOG_ERROR, "Some restrictions for inter prediction are broken, skipping macroblock\n");
> +        }
>

What is the actual problem you are trying to detect?  Missing reference
picture?

-- 
M?ns Rullg?rd
mans at mansr.com