[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
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