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.
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