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[Debconf-video] Fixing broken audio in 1078 and 1079


As you might know, two (or more) videos have problems with sound, the
pitch isn't correct:


The most likely reason is a sample rate mismatch, that is, data that's
actually 44100Hz is presented and played back as 48000Hz. As with tapes
or vinyl running at the wrong speed, this alters the pitch.

It's possible to fix it afterwards, let me point out what I did and
what's missing:

0. wget

1. oggz-rip -c vorbis -o audio.ogg 1078_Debconf_opening_plenary.ogv
2. Fire up your favourite hex editor and change 80 BB to 44 AC at offset
3. audio.ogg is now 44100 without reencoding or whatsoever
4. oggz-rip -c theoro -o video.ogv 1078_Debconf_opening_plenary.ogv

Unfortunately, the lengths of video.ogv and audio.ogg differ, the audio
file is "slower".

In a final step, one would mux audio and video back together, either the
video being slowed down or the audio being speed up. The latter can be
achieved with "sox tempo 0.918" or with ardour's timestretching tool.

If you want to try it on your own without a hex editor (lfhex, tweak or
whatever you prefer), you can also decode audio.ogg with oggdec to wav
(or run mplayer -ao pcm on the ogv) and then use play -r 44100 on the
resulting wav file. (play is provided the sox package)

I suggest to forget about the ogg and go back to the DV material. It
probably contains the uncompressed PCM audio tracks. I would demux them
or directly encode with the right flags passed to ffmpeg, indicating the
correct audio sample rate.

Useful shortcut:

  $ sox -r 44100 infile.wav outfile.wav

  Alters the header information of a wav file to 44100Hz.

Let me know how to proceed.


mail: adi@thur.de  	http://adi.thur.de	PGP/GPG: key via keyserver

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