[FFmpeg-devel] [PATCH] MSN Messenger TCP Webcam streams demuxer

[Ramiro Polla]

Hello,

Michael Niedermayer wrote:
> On Tue, Mar 11, 2008 at 06:55:53PM -0300, Ramiro Polla wrote:
>> Hello,
>>
>> Attached patch implements a demuxer for the TCP Webcam streams used by MSN 
>> Messenger. The Mimic codec in my previous patch is used for them.
>>
>> Such files are created by MSN Webcam Recorder, aMSN and Mercury Messenger.
>>
>> Oh, and before anyone asks me to drop the TCP in the name, MSN Webcam 
>> Recorder also records UDP transmissions into a different format. I'll 
>> probably implement it when all this gets in...
> [...]
>> static unsigned int find_valid_start_byteio(ByteIOContext *pb)
>> {
>>     char buf[HEADER_SIZE];
>>     uint64_t pos = 0;
>>     int ret;
>>
>>     for(;;) {
>>         url_fseek(pb, pos, SEEK_SET);
>>         if((ret = get_buffer(pb, buf, HEADER_SIZE)) != HEADER_SIZE)
>>             return -1;
>>         if((ret=find_valid_start(buf, HEADER_SIZE)) != -1)
>>             return pos;
>>         pos++;
>>     }
>>     /* Should never be reached, unless format was forced and not probed */
>>     return -1;
>> }
> 
> ret is unused, also this ++, seek back get_buffer() looks quite inefficient.
> And will not work on non seekable input.

Removed ret and get_buffer.

>> static int msnwc_tcp_read_header(AVFormatContext *ctx, AVFormatParameters *ap)
>> {
>>     ByteIOContext *pb = ctx->pb;
>>     AVCodecContext *codec;
>>     AVStream *st;
>>     uint64_t pos;
>>
>>     st = av_new_stream(ctx, 0);
>>     if(!st)
>>         return AVERROR_NOMEM;
>>
>>     codec = st->codec;
>>     codec->codec_type = CODEC_TYPE_VIDEO;
>>     codec->codec_id = CODEC_ID_MIMIC;
> 
>>     codec->codec_tag = CODEC_ID_MIMIC;
> 
> isnt that ML20 the codec tag ?

Oops...

>>     codec->extradata_size = MIMIC_HEADER_SIZE;
>>     codec->extradata = av_malloc(codec->extradata_size);
>>     if(!codec->extradata)
>>         return AVERROR_NOMEM;
>>
>>     av_set_pts_info(st, 32, 1, 1000);
>>
>>     pos = find_valid_start_byteio(pb);
>>     if(pos == -1)
>>         return -1;
>>
>>     if(pos)
>>         av_log(ctx, AV_LOG_DEBUG, "skipped %d bytes of trash\n", pos);
>>
>>     // Get width/height
>>     url_fseek(pb, pos, SEEK_SET);
>>     url_fskip(pb, 2);
>>     codec->width  = get_le16(pb);
>>     codec->height = get_le16(pb);
> 
> Please get rid of the backward seeking.

Done.

>>     // Get extradata
>>     url_fseek (pb, pos + HEADER_SIZE, SEEK_SET);
>>     get_buffer(pb, codec->extradata, MIMIC_HEADER_SIZE);
>>     url_fseek (pb, pos, SEEK_SET);
> 
> This looks very suspicious, dont tell me you place the header of the first
> packet in extradata this is definitly not ok.

Yes, that's what was happening...

Implemented differently with no extradata and no get_buffer + fseek.

Ramiro Polla
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