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

Michael Niedermayer michaelni
Mon Nov 1 01:31:38 CET 2010


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

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

Observe your enemies, for they first find out your faults. -- Antisthenes
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20101101/c03e46d8/attachment.pgp>



More information about the ffmpeg-devel mailing list