> This may (perhaps) have been an oversight. The “JPEGVideoRTPSource” code
> basically just implements the code that’s in Appendix B of RFC 2435 (which
> defines the RTP payload format for JPEG video). I.e., it
> transforms the information that was in the special RTP JPEG header (and
> quantization tables, if present) into a corresponding JPEG image header.
> It’s possible that this code is incomplete.
Appendix B does specifically state that the code there is only for 8 bit
precision quantization tables, but here is a code snippet for recognising the
presence of double precision tables:
(first uncomment the declaration of precision at line 384, then insert this
after the declaration of length on the next line)
unsigned curLen = 0;
unsigned numtables = 0;
for (int i = 8; i >= 0; i--) //each bit in the Precision field indicates value
of a table read from right to left; 0 for 8 bit, 1 for 16 bit (see RFC 2435
section 3.1.8)
{
if(curLen >= Length) break; //Ignore excess bits after all tables are
accounted for.
numtables++;
curLen += 64 * ((Precision & (1 << i - 1) + 1); //Set up for when 16
bit tables become supported. Equivalent to 64 * ((Precision & 2^(i-1)) + 1).
if((Precision & (1 << i - 1) == 0) return False; //Currently
unsupported - 16 bit precision table.
}
Regards
Josh Hitchen
Development
Metro Security (GB) PLC
www.metrosecurity.co.uk
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