[FFmpeg-devel] [PATCH] Fix empty G-VOP header decoding in MPEG-4

[Anatoly Nenashev]

On 12.02.2011 17:41, M?ns Rullg?rd wrote:
> Anatoly Nenashev<anatoly.nenashev at ovsoft.ru>  writes:
>
>    
>> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
>> index 5303da3..e0ef4bd 100644
>> --- a/libavcodec/mpeg4videodec.c
>> +++ b/libavcodec/mpeg4videodec.c
>> @@ -1493,17 +1493,20 @@ end:
>>
>>   static int mpeg4_decode_gop_header(MpegEncContext * s, GetBitContext *gb){
>> -    int hours, minutes, seconds;
>> +    int hours, minutes, seconds, marker;
>> +    int val;
>>
>> -    hours= get_bits(gb, 5);
>> -    minutes= get_bits(gb, 6);
>> -    skip_bits1(gb);
>> -    seconds= get_bits(gb, 6);
>> +    val= show_bits(gb, 18);
>> +    marker= val&  0x40;
>>
>> -    s->time_base= seconds + 60*(minutes + 60*hours);
>> -
>> -    skip_bits1(gb);
>> -    skip_bits1(gb);
>> +    if (marker) {
>> +        hours= (val>>  13)&  0x1F;
>> +        minutes= (val>>  7)&  0x3F;
>> +        seconds= val&  0x3F;
>> +        s->time_base= seconds + 60*(minutes + 60*hours);
>> +    } else {
>> +        av_log(s->avctx, AV_LOG_WARNING, "marker bit in GOP header is not set\n");
>> +    }
>>
>>       return 0;
>>   }
>>      
> Patch with nicer formatting attached.
>
>    
>
>
> > From 4583e1bf4c279fffd653682f480c21bb6a975886 Mon Sep 17 00:00:00 2001
> From: Anatoly Nenashev<anatoly.nenashev at ovsoft.ru>
> Date: Thu, 10 Feb 2011 16:09:48 +0000
> Subject: [PATCH] mpeg4video: ignore broken GOP headers
>
> Some MPEG4 cameras produce files with empty GOP headers.
> This patch makes the decoder ignore such broken headers and proceed
> with the following I-frame.  Without this change, the following
> start code is missed resulting in the entire I-frame being skipped.
>
> Signed-off-by: Mans Rullgard<mans at mansr.com>
> ---
>   libavcodec/mpeg4videodec.c |   18 +++++++++---------
>   1 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
> index 673c4e8..ad38df7 100644
> --- a/libavcodec/mpeg4videodec.c
> +++ b/libavcodec/mpeg4videodec.c
> @@ -1494,16 +1494,16 @@ end:
>
>   static int mpeg4_decode_gop_header(MpegEncContext * s, GetBitContext *gb){
>       int hours, minutes, seconds;
> +    unsigned time_code = show_bits(gb, 18);
>
> -    hours= get_bits(gb, 5);
> -    minutes= get_bits(gb, 6);
> -    skip_bits1(gb);
> -    seconds= get_bits(gb, 6);
> -
> -    s->time_base= seconds + 60*(minutes + 60*hours);
> -
> -    skip_bits1(gb);
> -    skip_bits1(gb);
> +    if (time_code&  0x40) {     /* marker_bit */
> +        hours   = time_code>>  13;
> +        minutes = time_code>>   7&  0x3f;
> +        seconds = time_code&  0x3f;
> +        s->time_base = seconds + 60*(minutes + 60*hours);
> +    } else {
> +        av_log(s->avctx, AV_LOG_WARNING, "GOP header missing marker_bit\n");
> +    }
>
>       return 0;
>   }
>    
>    

This patch looks better than mine, thus it would be great to commit it. 
But  I don't know has my opinion any matter due to new policy of review 
which I don't clearly understand.