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

Anatoly Nenashev anatoly.nenashev
Tue Nov 2 01:16:04 CET 2010


On 02.11.2010 01:32, Michael Niedermayer wrote:
> On Tue, Nov 02, 2010 at 12:12:16AM +0300, Anatoly Nenashev wrote:
>    
>> On 01.11.2010 23:56, Anatoly Nenashev wrote:
>>      
>>> On 01.11.2010 22:10, Michael Niedermayer wrote:
>>>        
>>>> On Mon, Nov 01, 2010 at 09:42:06PM +0300, Anatoly Nenashev wrote:
>>>>          
>>>>> On 01.11.2010 15:55, Michael Niedermayer wrote:
>>>>>            
>>>>>> On Mon, Nov 01, 2010 at 11:52:54AM +0300, Anatoly Nenashev wrote:
>>>>>>
>>>>>>              
>>>>>>> On 01.11.2010 03:31, Michael Niedermayer wrote:
>>>>>>>
>>>>>>>                
>>>>>>>> On Mon, Nov 01, 2010 at 02:56:50AM +0300, Anatoly Nenashev wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>                  
>>>>>>>>> On 01.11.2010 01:17, Michael Niedermayer wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>                    
>>>>>>>>>> On Sun, Oct 31, 2010 at 09:23:13PM +0300, Anatoly Nenashev wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>>>> Patch for .mxg demuxer
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>                        
>>>>>>>>>> [...]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>>>> +static int mxg_read_header(AVFormatContext *s,
>>>>>>>>>>> AVFormatParameters *ap)
>>>>>>>>>>> +{
>>>>>>>>>>> +    AVStream *video_st = 0, *audio_st = 0;
>>>>>>>>>>> +    MXGContext *mxg = s->priv_data;
>>>>>>>>>>> +
>>>>>>>>>>> +    /* video parameters will be extracted from the
>>>>>>>>>>> compressed bitstream */
>>>>>>>>>>> +    video_st = av_new_stream(s, VIDEO_STREAM_INDEX);
>>>>>>>>>>> +    if (!video_st)
>>>>>>>>>>> +        return AVERROR(ENOMEM);
>>>>>>>>>>> +    video_st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
>>>>>>>>>>> +    video_st->codec->codec_id = CODEC_ID_MXPEG;
>>>>>>>>>>> +    av_set_pts_info(video_st, 64, 1, 1000000);
>>>>>>>>>>> +
>>>>>>>>>>> +    audio_st = av_new_stream(s, AUDIO_STREAM_INDEX);
>>>>>>>>>>> +    if (!audio_st)
>>>>>>>>>>> +        return AVERROR(ENOMEM);
>>>>>>>>>>> +    audio_st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
>>>>>>>>>>> +    audio_st->codec->codec_id = CODEC_ID_PCM_ALAW;
>>>>>>>>>>> +    audio_st->codec->channels = 1;
>>>>>>>>>>> +    audio_st->codec->sample_rate = 8000;
>>>>>>>>>>> +    audio_st->codec->bits_per_coded_sample = 8;
>>>>>>>>>>> +    audio_st->codec->block_align = 1;
>>>>>>>>>>> +
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>                        
>>>>>>>>>>                      
>>>>>>>>>>> +    mxg->buffer = (uint8_t*) av_malloc(DEFAULT_PACKET_SIZE);
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>                        
>>>>>>>>>> unneeded cast
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>> removed
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>                    
>>>>>>>>>> [...]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>>>> +        if (mxg->found_video_packet) {
>>>>>>>>>>> +            mxg->buffer[mxg->current_pos++] = data;
>>>>>>>>>>> +            if (mxg->state == 0xfffe) {
>>>>>>>>>>> +                int size = get_be16(s->pb);
>>>>>>>>>>> +                if (url_feof(s->pb) || url_ferror(s->pb))
>>>>>>>>>>> +                    return AVERROR_EOF;
>>>>>>>>>>> +                mxg->buffer =
>>>>>>>>>>> av_fast_realloc(mxg->buffer,&mxg->buffer_size,
>>>>>>>>>>> +
>>>>>>>>>>> mxg->current_pos + size);
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>                        
>>>>>>>>>> here the + and similar at other points can overflow and
>>>>>>>>>> lead to realloc to a
>>>>>>>>>> too small buffer
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>> fixed
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>                    
>>>>>>>>>> [...]
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>>>> +            if (mxg->current_pos>= mxg->buffer_size) {
>>>>>>>>>>> +                mxg->buffer = (uint8_t*)
>>>>>>>>>>> av_fast_realloc(mxg->buffer,&mxg->buffer_size,
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>                        
>>>>>>>>>> unneeded cast
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>                      
>>>>>>>>> removed
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>                    
>>>>>>>> [...]
>>>>>>>>
>>>>>>>>
>>>>>>>>                  
>>>>>>>>> +static int mxg_read_packet(AVFormatContext *s, AVPacket *pkt)
>>>>>>>>> +{
>>>>>>>>> +    int ret, size;
>>>>>>>>> +    MXGContext *mxg = s->priv_data;
>>>>>>>>> +
>>>>>>>>> +    while(!url_feof(s->pb)&&     !url_ferror(s->pb)) {
>>>>>>>>> +        uint8_t data;
>>>>>>>>> +        int found_frame_end = 0;
>>>>>>>>> +
>>>>>>>>> +        if (mxg->state == 0xffed) {
>>>>>>>>> +            size = get_be16(s->pb);
>>>>>>>>> +            if (url_feof(s->pb) || url_ferror(s->pb))
>>>>>>>>> +                return AVERROR_EOF;
>>>>>>>>> +            if (size<= 14)
>>>>>>>>> +                return AVERROR(EINVAL);
>>>>>>>>> +            url_fskip(s->pb, 12);
>>>>>>>>> +            if (url_feof(s->pb))
>>>>>>>>> +                return AVERROR_EOF;
>>>>>>>>> +            size -= 14;
>>>>>>>>> +            ret = av_get_packet(s->pb, pkt, size);
>>>>>>>>> +            if (ret<     0)
>>>>>>>>> +                return ret;
>>>>>>>>> +
>>>>>>>>> +            pkt->stream_index = AUDIO_STREAM_INDEX;
>>>>>>>>> +            mxg->state = 0;
>>>>>>>>> +
>>>>>>>>> +            return pkt->size;
>>>>>>>>> +        }
>>>>>>>>> +
>>>>>>>>> +        data = get_byte(s->pb);
>>>>>>>>> +        mxg->state = (mxg->state<<     8) | data;
>>>>>>>>> +
>>>>>>>>> +        if (mxg->found_video_packet) {
>>>>>>>>> +            mxg->buffer[mxg->current_pos++] = data;
>>>>>>>>> +            if (mxg->state == 0xfffe) {
>>>>>>>>> +                int size = get_be16(s->pb);
>>>>>>>>> +                if (url_feof(s->pb) || url_ferror(s->pb))
>>>>>>>>> +                    return AVERROR_EOF;
>>>>>>>>> +
>>>>>>>>> +                if (mxg->current_pos>     mxg->current_pos + size)
>>>>>>>>> +                {
>>>>>>>>> +                    av_log(s, AV_LOG_ERROR, "buffer overflow\n");
>>>>>>>>> +                    return AVERROR(ENOMEM);
>>>>>>>>> +                }
>>>>>>>>> +                mxg->buffer =
>>>>>>>>> av_fast_realloc(mxg->buffer,&mxg->buffer_size,
>>>>>>>>> +
>>>>>>>>> mxg->current_pos + size);
>>>>>>>>> +                if (!mxg->buffer) {
>>>>>>>>> +                    av_log(s, AV_LOG_ERROR, "mxg demuxer
>>>>>>>>> error in av_fast_realloc()\n");
>>>>>>>>> +                    return AVERROR(ENOMEM);
>>>>>>>>> +                }
>>>>>>>>> +                if (size<     2) {
>>>>>>>>> +                    av_log(s, AV_LOG_ERROR, "wrong comment
>>>>>>>>> buffer size\n");
>>>>>>>>> +                    return AVERROR(EINVAL);
>>>>>>>>> +                }
>>>>>>>>> +                mxg->buffer[mxg->current_pos++] = size>>     8;
>>>>>>>>> +                mxg->buffer[mxg->current_pos++] = size&     0xff;
>>>>>>>>> +
>>>>>>>>> +                ret = get_buffer(s->pb, mxg->buffer +
>>>>>>>>> mxg->current_pos, size - 2);
>>>>>>>>> +                if (ret<     0)
>>>>>>>>> +                    return ret;
>>>>>>>>> +                if (ret>= 16&&     !strncmp(mxg->buffer +
>>>>>>>>> mxg->current_pos, "MXF", 3)) {
>>>>>>>>> +                    mxg->dts = AV_RL64(mxg->buffer +
>>>>>>>>> mxg->current_pos + 8);
>>>>>>>>> +                }
>>>>>>>>> +                mxg->current_pos += ret;
>>>>>>>>> +                mxg->state = 0;
>>>>>>>>> +            } else if (mxg->state == 0xffd9) {
>>>>>>>>> +                found_frame_end = mxg->current_pos;
>>>>>>>>> +                mxg->current_pos = 0;
>>>>>>>>> +                mxg->found_video_packet = 0;
>>>>>>>>> +            } else if (mxg->state == 0xffd8) {
>>>>>>>>> +                //emulating frame end
>>>>>>>>> +                found_frame_end = mxg->current_pos - 2;
>>>>>>>>> +                mxg->current_pos = 2;
>>>>>>>>> +                mxg->found_video_packet = 1;
>>>>>>>>> +            } else if (mxg->state == 0xffed) {
>>>>>>>>> +                //emulating frame end
>>>>>>>>> +                found_frame_end = mxg->current_pos - 2;
>>>>>>>>> +                mxg->current_pos = 0;
>>>>>>>>> +                mxg->found_video_packet = 0;
>>>>>>>>> +            }
>>>>>>>>> +
>>>>>>>>> +            if (found_frame_end) {
>>>>>>>>> +                ret = av_new_packet(pkt, found_frame_end);
>>>>>>>>> +                if (ret<     0)
>>>>>>>>> +                    return ret;
>>>>>>>>> +                memcpy(pkt->data, mxg->buffer, found_frame_end);
>>>>>>>>> +                pkt->stream_index = VIDEO_STREAM_INDEX;
>>>>>>>>> +                pkt->dts = mxg->dts;
>>>>>>>>> +                return pkt->size;
>>>>>>>>> +            }
>>>>>>>>> +
>>>>>>>>> +            if (mxg->current_pos>= mxg->buffer_size) {
>>>>>>>>> +                if (mxg->current_pos>     mxg->current_pos
>>>>>>>>> + DEFAULT_PACKET_SIZE)
>>>>>>>>> +                {
>>>>>>>>> +                    av_log(s, AV_LOG_ERROR, "buffer overflow\n");
>>>>>>>>> +                    return AVERROR(ENOMEM);
>>>>>>>>> +                }
>>>>>>>>> +                mxg->buffer =
>>>>>>>>> av_fast_realloc(mxg->buffer,&mxg->buffer_size,
>>>>>>>>> +
>>>>>>>>> mxg->current_pos + DEFAULT_PACKET_SIZE);
>>>>>>>>> +                if (!mxg->buffer) {
>>>>>>>>> +                    av_log(s, AV_LOG_ERROR, "mxg demuxer
>>>>>>>>> error in av_fast_realloc()\n");
>>>>>>>>> +                    return AVERROR(ENOMEM);
>>>>>>>>> +                }
>>>>>>>>> +            }
>>>>>>>>> +        } else if (mxg->state == 0xffd8){
>>>>>>>>> +            mxg->found_video_packet = 1;
>>>>>>>>> +        }
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>                    
>>>>>>>> This loop is a bit oddly structured, is there a reason for this?
>>>>>>>> id expect it to be more of the form
>>>>>>>> while {
>>>>>>>> state= (state<<8) + ...
>>>>>>>>
>>>>>>>> if(state ==)
>>>>>>>> else if
>>>>>>>> else if
>>>>>>>> else
>>>>>>>> }
>>>>>>>>
>>>>>>>> but its kind of convoluted with the audio code being before
>>>>>>>> the state update
>>>>>>>> then found_video_packet=1 and checks for that
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>                  
>>>>>>> Reimplemented. I hope that new version is more canonical.:-)
>>>>>>>
>>>>>>>                
>>>>>> no its the same
>>>>>> id like to understand why it is so convolutedly written if there
>>>>>> is a reason
>>>>>> why this is needed
>>>>>> If its really needed this has to be documented so someone doesnt
>>>>>> waste time
>>>>>> rewriting it to half the code.
>>>>>> And if there is no reason it should be simplified
>>>>>>
>>>>>>
>>>>>>              
>>>>> The principal reason consists in the following. If demuxer yet hasn't
>>>>> found a starting marker for package video it should check much less
>>>>> conditions, than in other case. Moreover in the second case it should
>>>>> copy data from incoming stream into the internal buffer because we
>>>>> don't
>>>>> know the size of video packet. That's why I have divided these two
>>>>> cases
>>>>> in a program code in hope that so will be faster.
>>>>>            
>>>> I thought there is just audio and video
>>>> What you say makes one belive that there are significant amounts of
>>>> other
>>>> things, besides
>>>>          
>>> Yes, this is that case. If the data is received from http they can
>>> contain some additional information in the beginning of each frame
>>> like this
>>> 0019fa0: 5454 d5d7 d6d6 d50d 0a2d 2d4d 4f42 4f54  TT.......--MOBOT
>>> 0019fb0: 4958 5f46 6173 745f 5365 7276 6572 7075  IX_Fast_Serverpu
>>> 0019fc0: 7368 0d0a 436f 6e74 656e 742d 7479 7065  sh..Content-type
>>> 0019fd0: 3a20 696d 6167 652f 6a70 6567 0d0a 0d0a  : image/jpeg....
>>> 0019fe0: ffd8 ffe0 0010 4a46 4946 0001 0100 0001  ......JFIF......
>>> .........
>>>
>>>
>>>        
> the video frames must be pretty small if that makes significant amounts of
> data
>    
Ok. New implementation is attached.
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