[MEncoder-users] Bug: Mono show 2 channels????

[Mike Hodson]

On 2/18/07, GeBu <gebu at seznam.cz> wrote:
> Thank you very much - it is big help for me. First I encoded video by
> Avidemux (Windows) and I had the same problem, but with every player. So
> I thought that it is problem of Avidemux and tried mencoder (Linux). And
> I got the same by mplayer. I thought that our script is bad. I was
> confused :(. Later I saw that it is ok in VLC and other player. So I did
> not know if the sound is mono or stereo.
I'm not sure why mplayer doesn't give a bit more precise indication of
this, but it would be nice as some sort of debug option...

> My idea was: maybe it is not right to have samplerate 48000 kHz for mono
> and bitrate 64 kbit/s.
> BTW: What is optimal parametres (bitrate, samplerate is there any
> relationship between them?) for mono audio (mainly speech) typically
> home video from DV cammera microfon?
> Jirka (GeBu)

Well, coming from a DV camera, you will always have 48000Hz for audio.
I wouldn't suggest changing this because resampling can cause noise
and distortion if the resample filter isn't having a good day; and in
reality there won't be much difference.  Bitrate vs. samplerate is
another matter; the higher the frequencies are that the encoder is
encoding, the more bitrate will be used at any given quality.  lame
usually does a good job of using a low-pass filter to compensate for
this, effectively reducing if not completely elimintating higher
frequencies, without distorting the rest of the spectrum like
resampling can.

 For your audio source, I would say 80 is good for mono, while stereo
can make use of channel-coupling so 128kbit sounds ok for most things.
You may also be asking why "stereo" can be effectively less bitrate
than 2xMono: this is because MP3 makes use of "mid/side" stereo,
encoding the 'middle' and the 'side' sounds seperately. Most things
are fairly 'centered' within the audio space so they will sound much
better than if you had 2 completely separate channels.

Mike