[vlc] VLC streaming in mono = 'slow' sound

[Gavin Hamill]

I'm trying to set up a low-bitrate stream from my home cable modem with
128kbps upstream... so at most I want the resulting stream to run at
112kbps, and ideally less.

I'm using Debian with a 'full feature' DVB card - onboard MPEG2 decoder
- it makes the video available as a video4linux device, and I have the
sound from this card looped through to the line-in on my sound card.

vlc v4l:/dev/video:norm=pal:size=320x240 --sout
'#transcode{vcodec=mp4v,vb=48,acodec=mpga,ab=32,channels=2}:std{access=http,mux=ogg,url=:80}'

This works, and mplayer shows this when I connect to the HTTP stream:
AUDIO: 44100 Hz, 2 ch, s16le, 32.0 kbit/2.27% (ratio: 4000->176400)

However, the audio quality at 32kbps mpeg1 layer 2 is dreadful, and I
want to get better quality by using a mono soundtrack at the same
bandwidth.

So, I replace channels=2 with channels=1, and mplayer now shows:

AUDIO: 44100 Hz, 1 ch, s16le, 32.0 kbit/4.54% (ratio: 4000->88200)

The soundtrack I get is played at the right speed, but the pitch is
about 2 octaves lower - normal speech sounds like some dreadful 'the
voices have been changed to protect the innocent' thing :)

If this isn't a known-issue, is there some stereo -> mono downmix audio
filter in VLC I can use before passing the data to the mpeg audio
encoder?

I'm using VLC 0.8.1.svn20050314-1 which comes with Debian sarge.

Cheers,
Gavin,


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