[theora] Add an intro to a theora file without re-encoding?

yorn at gmx.net yorn at gmx.net
Wed Jul 22 08:30:00 PDT 2009

> using some programs, that do reencoding. 
> Thank you very much for these details! I hope I can do without
> reencoding, because my files are huge.
> Anyway, I don't think I would be able to use ffmpeg2theora to do this:
> when I send multiple files to its standard input, it just stops after
> receiving the first file, as it things that the stream is over.
> By the way, would you mind looking at a related problem with oggCat, if
> you can, please? Here's what I ran:
> oggCat output.ogv intro-nosk.ogv trailer.ogv
> All the files can be found on
> http://free-electrons.com/issues/oggvideotools-jul22-2009/
> The audio stream in output.ogv sounds crappy. Both input files look all
> right (sample bitrates and sampling frequencies), but generated
> intro-nosk.ogv file may not be perfect ("nosk" means that I removed the
> skeleton part with "oggzrip").

I've discussed something like that with ^j some time ago. I think, the codebook for vorbis does not match for both files. There are several ways how to do the encoding vbr, abr, with upper and lower threshold etc. As far as I understood it is mainly for the encoding process, however sometimes these streams, even if they match in the average bitrate, sample rate etc, they are not really "equal".

I think, here we need a vorbis expert to explain that a bit more.

However. What I do is using oggResize (newest version) This does the reencoding for the audio stream without doing any harm on the video (so this is quite fast). So when I do:

# oggResize -D64000 intro-nosk.ogv intro-nosk2.ogv
# oggResize -D64000 trailer.ogv trailer2.ogv
# oggCat output2.ogv intro-nosk2.ogv trailer2.ogv

everything is fine (hopefully) ...

And you don't have to delete the skeleton before ;-).


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