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

Darren Wilkinson lintv at chipsugar.plus.com
Sun Oct 15 14:05:54 CEST 2006

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.

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