[XviD-devel] Bframes almost finished

[peter ross]

>From: Christoph Lampert <chl@math.uni-bonn.de>
>Reply-To: xvid-devel@xvid.org
>To: xvid-devel@xvid.org
>Subject: [XviD-devel] Bframes almost finished
>Date: Mon, 15 Jul 2002 00:28:42 +0200 (CEST)
>
>Hi,
>
>I worked a little at bframes this weekend. I added direct mode
>(without delta vector, but already saving bits) and corrected
>some errors in decoder_bframe by MinChem

great news.

>In particular the quantizer was hardcoded to 8 for blocks without
>dquant-modifier, which caused image distorsion.
>
>
>My new version seems visually fine, but I have a problem which
>I want to get rid off before I commit. Have a look at this test
>(Foreman QCIF, fixed quant 4, bquant_ratio=200, max_bframes=2):
>
>I encode and decode at the same time (with an offset of 4 frames,
>so it looks a little garbled)... There is lot of debug output,
>please look at the Time= N  values:
>
>They start fine, with 0(I) 3(P) 1(B) 2(B) 6(P) 4(B) 5(B) etc.
>but then after Frame   28: and DecFrame   28: the P-frame(!) decoding
>seems to "fail": it returns after 5 decoded bytes instead of 6 as usual
>and the timestamp is 2 instead of 27. After that, bytestream seems to be
>broken, the B-frame is identified correctly, but time_bp/time_pp is wrong
>and the image gets buggy.
>
>Do you have any idea what could cause _P-frames_ to become broken?
>This does not happen for max_bframes=0. :-(((

does the same problem occur when max_bframes=1? are you using 
dx50bvop-compatiblity? iam fairly sure there's a problem with 
dx50bvop-compatibility when max_bframes > 1.

it also looks like you're using packed mode. for testing, i would advise 
against PACKED and DX50BVOP encoding, and just use msfdam for decoding.
- PACKED groups P and B frames together in the one bitstream segment, AND 
adds NVOPS *with previously use timestamps* to remain compatible with divx5.
- DX50BVOP prevents the use of an I-frames as a future reference.

the last time i looked at the xvid bframes decoder, it did NOT handle packed 
bitstreams. iam planning to fix it, eventually.

-- pete


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