[FFmpeg-devel] [PATCH 2/2] MxPEG decoder
Michael Niedermayer
michaelni
Mon Nov 1 20:10:24 CET 2010
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
last= byte;
byte= get_byte(s->pb);
if(last == 0xFF){
if(byte==
...
else if
...
}
could be used to reduce the checks if they really matter speedwise
[...]
--
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