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

[Michael Niedermayer]

On Wed, Nov 03, 2010 at 06:11:11PM +0300, Anatoly Nenashev wrote:
> On 03.11.2010 03:21, Anatoly Nenashev wrote:
>> On 02.11.2010 22:08, Michael Niedermayer wrote:
>>> On Tue, Nov 02, 2010 at 06:25:41AM +0300, Anatoly Nenashev wrote:
>>>
>>> [...]
>>>> +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)) {
>>>> +        const uint8_t data = get_byte(s->pb);
>>>> +        unsigned int found_frame_end = 0;
>>>> +        mxg->state = (mxg->state<<  8) | data;
>>>> +        mxg->buffer[mxg->current_pos++] = data;
>>>> +
>>>> +        if (mxg->state == 0xffd9) {
>>>> +            found_frame_end = mxg->current_pos;
>>>> +        } else if (mxg->state == 0xffd8) {
>>>> +            if (mxg->vop_found) {
>>>> +                //emulating frame end
>>>> +                found_frame_end = mxg->current_pos - 2;
>>>> +                url_fseek(s->pb, -2, SEEK_CUR);
>>>> +            } else {
>>>> +                mxg->vop_found = 1;
>>>> +            }
>>>> +        } else if (mxg->state == 0xfffe) {
>>>> +            size = get_be16(s->pb);
>>>> +            if (url_feof(s->pb) || url_ferror(s->pb))
>>>> +                return AVERROR_EOF;
>>> checking for eof after every byte read seems overkill to me
>>>
>>>
>>
>> Removed.
>>
>>>> +
>>>> +            if (mxg->current_pos>  mxg->current_pos + size)
>>>> +                return AVERROR(ENOMEM);
>>>> +
>>>> +            mxg->buffer =  
>>>> av_fast_realloc(mxg->buffer,&mxg->buffer_size,
>>>> +                                          mxg->current_pos + size);
>>>> +            if (!mxg->buffer)
>>>> +                return AVERROR(ENOMEM);
>>>> +
>>>> +            if (size<  2) {
>>>> +                av_log(s, AV_LOG_ERROR, "wrong comment buffer  
>>>> size\n");
>>>> +                return AVERROR(EINVAL);
>>>> +            }
>>> checking size after using it
>>
>> It's moved above.
>>
>>>
>>>> +            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 == 0xffed) {
>>>> +            mxg->current_pos -= 2;
>>>> +            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) || url_ferror(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;
>>>> +        }
>>>> +
>>>> +        if (found_frame_end) {
>>>> +            mxg->vop_found = 0;
>>>> +            mxg->current_pos = 0;
>>>> +            ret = av_new_packet(pkt, found_frame_end);
>>>> +            if (ret<  0)
>>>> +                return ret;
>>>> +            memcpy(pkt->data, mxg->buffer, found_frame_end);
>>> avoidable
>>>
>>>
>>
>> Yes. New implementation attached.
>>
>>
>>
>
> Fix pkt->pos value initialization.
>
>
> I have additional question. This patch works fine with ffplay, so this  
> command
>         ./ffplay stream.mxg
> works fine and I see well syncronized video.
>
> But if I run
>         ./ffmpeg -i stream.mxg -f rawvideo /dev/null
> there are a lot of messages:
>         [rawvideo @ 0x30f4d10] st:0 error, non monotone timestamps 1 >= 1
>
> After some researches I found that right command line must be
> ./ffmpeg -i stream.mxg -r 25 -f rawvideo /dev/null
>
> So it meens that user must manually define output FPS, otherwise it will  
> be 1/time_base. In case of mxg demuxer it is 1000000.
> I think that it isn't so user friendly way. What can I do with this issue?

please show us what actual pts/dts values are being returned by your demuxer
maybe there is something wrong with them

also make sure  tb_unreliable() returns non zero

and i assume there is no true fps value stored in the file?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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