[FFmpeg-devel] [PATCH 1/2] MxPEG decoder

[Anatoly Nenashev]

On 01.11.2010 14:35, Michael Niedermayer wrote:
> On Mon, Nov 01, 2010 at 02:06:25AM +0300, Anatoly Nenashev wrote:
>    
>> On 01.11.2010 00:44, Michael Niedermayer wrote:
>>      
>>> On Sun, Oct 31, 2010 at 09:20:34PM +0300, Anatoly Nenashev wrote:
>>> [...]
>>>
>>>        
>>>> @@ -195,6 +198,37 @@ int ff_mjpeg_decode_dht(MJpegDecodeContext *s)
>>>>        return 0;
>>>>    }
>>>>
>>>> +static int mjpeg_allocate_picture(MJpegDecodeContext *s)
>>>> +{
>>>> +    if(s->picture.data[0])
>>>> +        s->avctx->release_buffer(s->avctx,&s->picture);
>>>> +
>>>> +    s->picture.reference= 0;
>>>> +    if(s->avctx->get_buffer(s->avctx,&s->picture)<   0){
>>>> +        av_log(s->avctx, AV_LOG_ERROR, "mjpeg get_buffer() failed\n");
>>>> +        return -1;
>>>> +    }
>>>> +
>>>> +    return 0;
>>>> +}
>>>> +
>>>> +static int mxpeg_allocate_picture(MJpegDecodeContext *s)
>>>> +{
>>>> +    if (s->mxctx.reference_picture.data[0])
>>>> +        s->avctx->release_buffer(s->avctx,&s->mxctx.reference_picture);
>>>> +    s->mxctx.reference_picture = s->picture;
>>>>
>>>>          
>>>
>>>        
>>>> +    s->picture.data[0] = s->picture.data[1] =
>>>> +        s->picture.data[2] = s->picture.data[3] = 0;
>>>>
>>>>          
>>> the indention is odd
>>>
>>>
>>>        
>> Just a feature of Emacs. Indention removed.
>>
>>      
>>>
>>>        
>>>> +
>>>> +    s->picture.reference= 1;
>>>>
>>>>          
>>>
>>>        
>>>> +    if(s->avctx->get_buffer(s->avctx,&s->picture)<   0){
>>>> +        av_log(s->avctx, AV_LOG_ERROR, "mxpeg get_buffer() failed\n");
>>>> +        return -1;
>>>> +    }
>>>>
>>>>          
>>> duplicate code
>>>
>>>
>>>
>>>        
>> May be not because "mxpeg_allocate_picture" used in two places:
>> ff_mjpeg_decode_sof and mxpeg_decode_mxm.
>>
>>      
>>> [...]
>>>
>>>        
>>>> @@ -788,14 +823,29 @@ static int mjpeg_decode_scan(MJpegDecodeContext *s, int nb_components, int Ah, i
>>>>            }
>>>>        }
>>>>
>>>> +    if (use_mxm_bitmask) {
>>>> +        if (s->mb_width*s->mb_height>   (s->mxctx.mxm_bitmask_size<<   3)) {
>>>> +            av_log(s->avctx, AV_LOG_ERROR, "MXM bitmask is not complete\n");
>>>> +            return -1;
>>>> +        }
>>>> +
>>>> +        init_get_bits(&mxm_bitmask_gb, s->mxctx.mxm_bitmask,
>>>> +                      s->mxctx.mxm_bitmask_size<<   3);
>>>> +
>>>> +        s->picture.pict_type= FF_P_TYPE;
>>>> +        s->picture.key_frame= 0;
>>>> +    }
>>>>        for(mb_y = 0; mb_y<   s->mb_height; mb_y++) {
>>>>            for(mb_x = 0; mb_x<   s->mb_width; mb_x++) {
>>>> +            const int copy_mb = use_mxm_bitmask&&   !get_bits1(&mxm_bitmask_gb);
>>>> +            if (!reference_picture_avail&&   copy_mb) continue;
>>>>
>>>>          
>>> cant use_mxm_bitmask be 0 when !reference_picture_avail
>>> (would avoid 1 check per mb)
>>>
>>>
>>>        
>> Fixed. Conditions are switched in "if()".
>>
>>      
>>> [...]
>>>
>>>        
>>>> @@ -1505,6 +1631,15 @@ not_the_end:
>>>>    the_end:
>>>>        av_log(avctx, AV_LOG_DEBUG, "mjpeg decode frame unused %td bytes\n", buf_end - buf_ptr);
>>>>    //    return buf_end - buf_ptr;
>>>> +
>>>> +    if (s->avctx->codec_id == CODEC_ID_MXPEG&&
>>>> +        !s->mxctx.has_complete_frame) {
>>>> +        if (s->picture.key_frame)
>>>> +            s->mxctx.has_complete_frame = 1;
>>>>
>>>>          
>>>
>>>        
>>>> +        else if (!(s->avctx->flags&   CODEC_FLAG_LOW_DELAY))
>>>> +            *data_size = 0;
>>>>
>>>>          
>>> mxpeg is always low delay, unless i misunderstand something
>>>
>>>
>>>
>>>        
>> Not absolutely so. Generally there's no I-Frame concept for MxPEG known
>> from other codecs. Every encoded frame contains some parts of all image.
>> All that we know is after fixed time delay we can collect a full puzzle.
>> Actually some cameras send full JPEG  frame in connection and this
>> feature is supported in attached patch but this is not that case on
>> which it is necessary to rely. That's why if CODEC_FLAG_LOW_DELAY is
>> disabled the decoder must collect a full image before return a first
>> decoded frame. Otherwise, if CODEC_FLAG_LOW_DELAY is enabled we may see
>> a frame full of holes at the start of played video.
>>      
> i see what you are trying to do but thats misusing that flag
> i think you will have to add a new flag for this, and h264 could use that too
>    
>
Ok. I will add a new flag. It might be called CODEC_FLAG_COLLECT_FRAME 
for example. But I don't understand how it can be used for h264.
H264 has I-frames (with IDR flag enabled) and there is no need to 
collect a full frame from the parts. Am I misunderstand something?