[linux-dvb] Re: dec2000-t success

[Alex Woods <linux-dvb@giblets.org>]

On Sunday 27 Apr 2003 10:08 am, Reiner Klenk wrote:
> On Sun, 27 Apr 2003, Bruce Janson wrote:
> > However, according to
> >
> >   http://www.linux-usb.org/linux.conf.au.02/talk/html/slide_5.html
> >   http://www.usb.org/faq/ans2#q1
> >
> > the DEC 2000-t's USB 1.1 interface will impose a 12 Mbits/s limit on
> > its USB->PC interface.  I do not know the maximum (compressed)
> > throughput that can be required by a 7 MHz, DVB-T transport stream
> > (23 Mbits/s?), but I suspect that it does exceed 12 Mbits/s.
> > If true, this would impose an unfortunate limitation on the DEC 2000-t.
> > (USB 2.x at 480 Mbits/s would have avoided this...)
>
> Yeah, I am a little confused here, too. I just tuned to one of the
> stations and mplayer tells me the video stream is:
>
>  MPEG2 720x576 (aspect 2)  25,00 fps 18750,0 kbps (2343,8 kbyte/s)
>
> plus the audio stream:
>
> Layer: 2  BRate: 192 kb/s  Freq: 48.0 kHz
>
> That would exceed the USB 1.1 data rate. Does this mean that the transport
> stream adds another level of compression ?
>
> Anyone knows whether the dec2000 can also handle ac3 audio streams ? If
> so, how can I extract them from the transport stream ?
>

Some of the videostream rates I've had reported from the dec, here in the UK, 
have been:

4MBit/s, 5.3Mbit/s, 6Mbit/s, 10Mbit/s and 15Mbit/s

These are from QAM16 and QAM64.  I've seen 15Mbit/s on both of these.  How it 
fits these down USB 1.1, I have no idea.  I'm neither a USB expert or a DVB 
expert.

The dec delivers the streams over usb in AVPES format, which consists of a 
video elementary stream and an audio packetised elementary stream.  
Presumably it uses this format to remove some of the bandwidth overhead of 
using a transport stream.  The dec driver constructs a fake transport stream 
from the AVPES in order to play nice with everything.  So, I don't think that 
AC3 streams can be got from the dec.

Cheers,
Alex


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