[XviD-devel] packed bitstream

Radek Czyz syskin at ihug.com.au
Sat Jul 12 01:25:38 CEST 2003


Hi,

I'm trying to create an mpeg4 parser (a small lib that will be able to
analyze m4v stream or frames and give information about it - matroska
project needs it).
I'm trying to figure out the meaning of N-VOPs in packed bitstream..
and I can't. What do they do? How can I tell if an N-VOP is dummy or
real? Also, what is exactly written to the 'empty' frame after packed
PB frame? (or maybe this is the N-VOP.. or maybe not).

Can anyone tell me please? :)

Ah, one more thing - imagine that you have a pure m4v stream with 0x7f
frames (yes I know current encraw doesn't do that - but what if) - is
there a way to tell if 0x7f byte was added, and remove it? Note that
I'm not decoding everything, only startcodes and headers - and 0x7f
looks exactly like what I would expect at the end of real frame, so I
can't just look at the byte before a startcode... but maybe there is a
simple way to do that?
If I don't do that and mux such stream to a container with 0x7f
included (it would stick to the end of previous frame), do you think
decoders will ignore it, or activate some kind of error correction?

Thanks in advance
Regards,
Radek



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