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

[Måns Rullgård]

Anatoly Nenashev <nenashev_as at mail.ru> writes:

>> 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.

You can obviously confirm whether it fixes your problem.  I tested it on
your sample, but another test run can never hurt.  If you do that, I
will push it.  It's had enough review.

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