[XviD-devel] trying to introduce resync markers

[Angela Belda]

Hi Everybody!
I am new here, in this mail list, but I have been working a while with 
xvid. I am interested in video streaming aplications and Java and I have 
created some JNI modules to acces the xvid encoder/decoder from Java 
code. Using Java Media Framework I can encode and decode live content 
using native xvid and transmit it over RTP.
Now I wanted to add the possibility to include resynchronization markers 
in a xvid encoded stream, because the decoder already supports this 
option and it didn't seem very difficult. I create the markers with the 
following method:

void write_video_packet_header(Bitstream * const bs,
                        const MBParam * pParam,
                        const FRAMEINFO * const frame,
                        int mbnum){

    int mbnum_bits = log2bin(pParam->mb_width *  pParam->mb_height - 1);
    uint32_t nbitsresyncmarker;
    int addbits=0;
    if (frame->coding_type != I_VOP)
        addbits = frame->fcode -1;
    if (frame->coding_type == B_VOP)
        addbits = max(frame->fcode, frame->bcode)-1;
    BitstreamPadAlways(bs);
    nbitsresyncmarker = NUMBITS_VP_RESYNC_MARKER + addbits;
    BitstreamPutBits(bs, RESYNC_MARKER, nbitsresyncmarker);
    BitstreamPutBits(bs, mbnum, mbnum_bits);
    BitstreamPutBits(bs, frame->quant, 5);
    BitstreamPutBit(bs, 0); /* hec */
}

Then I modify the methods FrameCodeI and FrameCodeP to reset MV 
prediction on boundaries. With I Frames I introduce a resync marker when 
the number of bits encoded reaches a specified value, as specified in 
the standard, but that seems not to possible with P frames, because I 
need to know where to reset the MV prediction before encoding. I have 
modified the method MotionEstimation to reset MV prediction  
periodically, each fixed number of macroblocks and it seems to work 
fine, but I am not sure what to do to introduce  the resync markers  as 
specified in the standard. Any ideas?
The next step is to detect this markers in Java and partitionate the 
encoded frames before encapsulating over RTP. I had the idea to create a 
new output parameter in the encoder. This new parameter would be an 
array of bitstream positions where resync markers were introduced. The 
other possibility would be to look for these resync markers direct in 
Java, before packetizing, but if I cannot know a fixed minimum number of 
bytes between resync markers I should look in the whole bitstrem, 
shouldn't I?. Any suggestions?

Thanks in advance,

Ángela