Klaus Frahm wrote:
> 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.
The machine will just be that modified xbox. The xbox has a 733Mhz
celeron processor which is why I asked about that processor. The xbox
does just have 64MB but if I use no desktop enviroment that shouldn't be
a worry.
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.
Those are all good points (esp about the usb hd) although the xbox can't
do usb 2 or pci cards.
_______________________________________________
linux-dvb mailing list
linux-dvb@xxxxxxxxxxx
http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
