[Theora-dev] Theora and Vorbis problems

illiminable ogg at illiminable.com
Wed May 24 12:12:13 PDT 2006


While it's true your file seems valid spec-wise, it suffers from being 
poorly multiplexed... ie coarse muxing.

This is the first video page
Page Location : 73374 to 77589
Ver No      : 0
Head Flags  :
Granule Pos : 254
Serial No   : 1792863441
Seq No      : 2
Checksum    : 279992667
Num Segs    : 255
Head Size   : 282
Data Size   : 3933
Page Size   : 4215
Num Packets : 255

There's about 20 pages of audio before the first video page, and the first 
video page contains 255 frames. This is due to the way ogg sorts pages by 
end-time, it causes pathological files to be created with the default paging 
algorithm particularly when the size of the video packets is small. VLC will 
probably play, but most others things probably won't. My directshow code has 
will only let there be about a 75 packet delta between current play time 
between streams. That's typically about 3 seconds, which is already pretty 
excessive. Everything could just make their buffers even bigger... but my 
position is that these files are broken and it's better to discourage people 
from making them, rather than making stupidly large buffers. Also files like 
this will cause problems as more embedded devices start to use theora.

 Basically the file is "ten seconds of audio data" then "ten seconds of 
video data" rather than being nicely interleaved. When you mux, particularly 
when you mux "easy" video such as this one, you have to make sure you flush 
the stream after some number of packets ~50 say, or some amount of time say 
1-2 seconds if more than that would normally continue to fit in one page. I 
think ffmpeg2theora is the only tool currently that properly does this.


----- Original Message ----- 
From: "Philip Heron" <phil at firestorm.cx>
To: "Theora Development" <theora-dev at xiph.org>
Sent: Thursday, May 25, 2006 1:29 AM
Subject: [Theora-dev] Theora and Vorbis problems

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