[FFmpeg-devel] [PATCH 1/2] avcodec/mlp_parser: don't try to combine frames when full frames are provided

[James Almer]

On 1/20/2018 7:15 AM, wm4 wrote:
> On Fri, 19 Jan 2018 20:30:59 -0300
> James Almer <jamrial at gmail.com> wrote:
> 
>> On 1/19/2018 5:06 PM, wm4 wrote:
>>> On Fri, 19 Jan 2018 16:51:45 -0300
>>> James Almer <jamrial at gmail.com> wrote:
>>>   
>>>> Attempting full frame reconstruction is unnecessary for containers
>>>> like Matroska, so just skip it altogether.
>>>>
>>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>>> ---
>>>>  libavcodec/mlp_parser.c | 4 ++++
>>>>  1 file changed, 4 insertions(+)
>>>>
>>>> diff --git a/libavcodec/mlp_parser.c b/libavcodec/mlp_parser.c
>>>> index 3c0330f777..4827354f18 100644
>>>> --- a/libavcodec/mlp_parser.c
>>>> +++ b/libavcodec/mlp_parser.c
>>>> @@ -256,6 +256,9 @@ static int mlp_parse(AVCodecParserContext *s,
>>>>      if (buf_size == 0)
>>>>          return 0;
>>>>  
>>>> +    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
>>>> +        next = buf_size;
>>>> +    } else {
>>>>      if (!mp->in_sync) {
>>>>          // Not in sync - find a major sync header
>>>>  
>>>> @@ -315,6 +318,7 @@ static int mlp_parse(AVCodecParserContext *s,
>>>>      }
>>>>  
>>>>      mp->bytes_left = 0;
>>>> +    }
>>>>  
>>>>      sync_present = (AV_RB32(buf + 4) & 0xfffffffe) == 0xf8726fba;
>>>>    
>>>
>>> Not so sure about this. I think some mkv TrueHD files contain packets
>>> that are not properly starting on frame boundaries. But I don't really
>>> remember.  
>>
>> As in badly muxed files? Couldn't the same thing happen with any other
>> codec? We're not bothering to consider such cases in other parses as far
>> as i could see.
> 
> From my hazy memory, this also happened with mp3, although the Matroska
> demuxer explicitly forces full parsing for that codec.

I guess i could force full parsing for truehd on matroska as well, but
it kinda defeats the point of this patch. There are not a lot of
containers that support it after all (mpegts is another, but that one
forces full parsing for everything).

Would that be ok?