[theora] Many improvements and a few problems

Alvaro Segura alvaro.segura at gmail.com
Sat Sep 19 06:28:39 PDT 2009


I must say I'm very impressed with improvments in the latest versions of 
the encoder, especially in 2-pass mode. I was trying encodes of videos 
with sudden changes from no or moderate motion, to high motion scenes. 
Most samples of Theora quality I saw on the net were very slow motion 
usually. These high-motion videos were especially hard for Theora and it 
quickly introduced unacceptable artifacts.

Now the encoder reacts better, and much better in two-pass. Just used 
ffmpef2theora nightly. Blockiness even at quite low bitrates almost 
desappears or gets to an acceptable level. Even tried a 720p50 HD video 
(I thought Theora would be very bad at that) and the result was quite 
good at around 9 Mb/s.

Now a couple possible problems:

1) One-pass can still improve I think, with a better and quicker 
adaptation to higher motion or detail parts, even going beyond the 
target bitrate for a moment, maybe. I tried -soft-target but I don't see 
a great difference.

2) Latest versions produce different OGG streams which challenge some 
players and splitters. I think the change has been somewhere between the 
stable ffmpeg2theora (march 2009) and this summers builds:

.OGV produced now are not recognized by MPC-HC's internal OGG splitter, 
which worked well for all files previously. If Haali splitter is 
installed, it can handle most files, but in some of them duration is 
incorrectly detected and the stop after a few seconds.

Has something changed in the OGG stream or in libogg or something?

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