Re: [Linphone-users] [linphone-develpers]questions on mediastreamer rfc 2190 generated packets

[Simon Morlat]

Hi Tian,

I'm sorry not to be able to help you. Indeed this code was contributed a few years ago by somebody I don't remind. I never studied in deep his patch, just verified it was basically working for receiving packets, and should also work for sending packet provided that there is no need to split at Macroblock level (which is the case at low bitrates < 80kbit/s).

Simon

Le Wednesday 20 May 2009 08:13:06 tian yun, vous avez écrit :
> Hi
>
> I'm now studying the RTP packetlization for H.263-1995 frame in linphone. I
> saw mediastreamer use the mode A in rfc2190 to split the frame, which means
> that the bitstream will be packetlized on a GOB boundary or a picture
> boundary. In the function get_gbsc(), the following code is used to split
> the frame:
>
> for (i = 2; i < len-4; i++) {
> buf = *((uint32_t *)(psc+i));
> for (j = 0; j < 8; j++) {
> if (((buf >> j) & 0x00FCFFFF) == 0x00800000) {/*PSC*/
> printf("-------%s: PSC, i=%d, j=%d, buf=%x\n", __func__, i,
> j, buf);
> i += 2;
> k=i;
> break;
> } else if (((buf >> j) & 0x0080FFFF) == 0x00800000) {/*GBSC*/
> printf("-------%s: GBSC,i=%d, j=%d, buf=%x\n", __func__, i,
> j, buf);
> i += 2;
> k = i;
> break;
> }
> }
> }
>
> I know the picture start code of H.263 is 0000 0000 0000 0000 100000 in 22
> bits and GSBC start code is 0000 0000 0000 0000 1 in 17 bit, why do
> get_gbsc() use the mask 0x00FCFFFF and 0x0080FFFF here to pick out the PSC
> and GSBC header? How does it identify?
>
> Thanks
> Best Regards
> Y.T.