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

Anatoly Nenashev anatoly.nenashev
Mon Nov 1 22:12:16 CET 2010


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......
> .........
>
>

More detailed description:
http://developer.mobotix.com/mobotix_sdk_1.0.2/docs/mxpeg_frame.html

See "MxPEG Live Stream" format.



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