Re: Real Time MP3 Encoding

[James Derrick <james@xxxxxxx>]

On Fri, 21 Jan 2000 15:32:36 -0000, you wrote:

>Hi All,
>
>Whilst we are on the subject of MP3 Jukebox functionality a quick =
question.
<snip>

>if I want to "tape" a 60
>minute radio program it would take over 600Mb of disk space. By
encoding=
it
>on the fly direct from the soundcard without an intermediate wav file
it
>will only take about 60Mb
Well, Keith, I've been doing just that for quite some time on my Linux
server to record Radio 4's "Science at 9:00" programs.

I have a script that records the audio as a WAV and then encodes it to
MP3 for serving to a client machine via NFS or Samba. This gives me a
'library' of science programs to listen to when I catch up with the
paperwork.

This approach gives give a couple of minor problems. All the MP3
encoders I've seen need a high bitrate (44k1- 32k samples/s) WAV file
to encode. You can't encode at 'radio-quality' and convert to MP3.
This means you need a bit of temp space. The encoding process then
takes a few hours so you can't really listen to a program that has
just finished using MP3 (although you could kill the encoder and hear
the WAV).

I did try a few experiments before adopting this approach and found
MP3 to be the best tradeoff of space and sound. I tried gzip'ed WAV
files which turn out to be actually a bit smaller than MP3 (6.8Mb for
30mins 8kHz mono PCM verses 7.8Mb 32kbps MP3), however these need to
be uncompressed on the client PC to be heard. WAV also sounds worse at
low bitrates with constant hiss, although music suffers from bad
frequency distortion under MP3.

I don't have stats for the MP3 encoding time as this just runs as a
batch job and isn't really noticeable. I use a PI-233 and BladeEnc-
the encode time is probably about 4x the length of the recording.

James
---
James Derrick    james@xxxxxxx, Cramlington, Near Newcastle, =
England
Forwarding Service: jderrick@xxxxxxx
Beyond the Horizon of the place we lived when we were =
young,
In a World of Magnets and Miracles. Pink Floyd.

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