[linux-dvb] Is a 733Mhz celeron enough & usb 1.1 sticks

Klaus Frahm frahm at irsamc.ups-tlse.fr
Sat Oct 14 22:43:11 CEST 2006

 > The reason I ask is that i'm interested in setting myself a new
 > project.
 > I'd like to use a modded xbox to run linux and thus use as a PVR. I'm
 > aware that linux on the xbox with usb support is no problem. What I'd
 > like to know is are there any dvb usb devices apart from the old
 > nova/dec from Hauppauge.
 > I'd also like know if anyone anyone else has done software mpeg2
 > decoding (DVD or standard definition DVB) on linux with a celeron
 > 700/733Mhz so I know if that processor is powerful enough.
 > All responses welcome.

I have been using a Pentium III, 500 Mhz with 640 MB of Ram to decode 
mpeg2 from DVB-T, ADSL-TV (from the Multiposte of my french internet 
provider Free who provides TV with the rtsp-protocol) and also for DVD.
The first two cases work very well to look TV on the computer screen, 
maybe 30-50 % CPU occupation. With DVD and 16/9 it works also but the 
CPU usage is a little bit more limit, there may be very very slight 
freezes from time to time. However if you have a DTS-track on the DVD 
and you want the computer to decode that plus the mpeg2 video than there 
is problem. The DTS-driver (which I used for vlc) is very very 
CPU-hungry, even with deactivating the video output I have nearly 100% 
of CPU-usage and with video it no longer works. However with standard 
AC3 tracks (Dolby Digital 5.1) there is no such problem.
I have also a very old and simple graphics card, 8 MB of Ram and far 
below actual standards of performance.

I believe your machine will be very okay provided you have enough memory 
(minimum 256 Mb, the more the better). However, I don't know what 
happens if you want to decode mpeg2 for a TV-analog Video/SVideo card 
(for a TV-connection). I suppose this will work but you should 
absolutely use a PCI card and no USB-device for this because with USB 
1.1 this will eat up your band width which you may still need for an 
USB-DVB-T device.

On my old computer the USB port is also 1.1 and I have also tested DVB-T 
with a USB-Tuner (an AverTV A800 USB 2.0 which compatible USB 1.1). In 
principle it works okay but USB 1.1 limits my bandwidth to about 900 
KB/s (measured with a USB-hard disk). Normally DVB-T is well below this 
value, in my case in France it is about 4-5 Mb/s = 500-600 KB/s (here: 
Mb/s = Megabits/s and KB = Kilobytes/s and 1 Mb/s = 128 KB/s). However 
in one case, with 16/9 and one particular channel (M6 in France) the 
bandwidth was quite close to the maximum and taking into account normal 
bandwidth fluctuations in the mpeg-bitrate (this is never constant in 
time!) I had in this particular case (modest) freezes due to USB-1.1 
speed limitations.
Furthermore with USB 2 on a better computer you can access to a full 
DVB-T-Multiplex, record several channels in the same time. This usage is 
of course impossible with USB 1.1.
Another problem with USB 1.1 is when you want connect a USB-harddisk and 
a USB-Tuner because they may share the bandwidth and this may not be 
enough to record directly on the USB-harddisk (this depends how many 
different USB-controlers you have but on an old PC there is probably 
only one even if there are two or more USB-ports).
These are the kind of limitations you may encounter. In general the 
processeur seems okay to me but you can have only one full-speed 
USB-device (either harddisk or USB-Tuner). If you have a PCI-DVB-T card 
the situation changes and you don't have USB 1.1 limitation.

Greetings, Klaus.

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