[linux-dvb] Speed of DVB audio decoding

[Radovan Garabik <garabik@melkor.dnp.fmph.uniba.sk>]

This is just a description of what I found out, maybe to help
others with similar problems...
My setup is PII 266 MHZ with Skystar2 (2.6B), which is about as
slow as you can get (but at least it has a good video card :-))

Watching TV under Windows is aceptable, channels with better resolutions
(such as Canale 5, Italia 1, german channels on Hotbird) are jerky,
but watchable (but switching channels takes forever).

First I tried to use mplayer, while low resolution channels were OK,
high resolutions were unwatchable. While experimenting with different
video and audio codecs, I accidentally found out that leaving sound out
makes the picture quite smooth. So I took a piece of audio and tried 
various mp2 players:
mplayer (with no video) eats about 15% CPU
mpg321 also 15%
madplay 10%
mpg123 (the nonfree one) about 6%, with downmixing to mono and
   downsampling even much less (2-3%)
so I went the difficult path of upgrading the system to install 
latext xine, and to my surpsise, picture was quite acceptable (maybe
a little bit worse then under Windows, but channel switching is fast)

IMHO xine uses libmad for audio decoding, and that 4% of CPU time seems
to make the needed difference.
I have yet to compile mplayer with libmad (it takes a while!) to 
see how it performs, but it is a pity mpg123 is nonfree - it
has been written a long time ago, when speed of decoding was very
important (I remember playing mp3's on 66 MHz 486 :-)), and nowadays
no-one bothers with such kind of optimalizations.


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| Radovan Garabík http://melkor.dnp.fmph.uniba.sk/~garabik/ |
| __..--^^^--..__    garabik @ melkor.dnp.fmph.uniba.sk     |
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