[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.
More information about the ffmpeg-devel
mailing list