[linux-dvb] Re: dec2000-t success

[Andy Coates <andy@bribed.net>]

Gavin Hamill (gdh@acentral.co.uk) wrote:
> On Sun, Apr 27, 2003 at 02:52:22PM +0100, Alex Woods wrote:
> > 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.
> 
> Yep, BBC ONE is marked at 15Mbit/sec, and all the BBC transmissions are 
> marked with a static bitrate... whilst the ITV ones show the real 
> bitrate - i.e. the marked bitrate will change every time you restart an 
> mplayer session on a live stream.
> 
> I don't believe BBC ONE is actually going anywhere near 15Mbit/sec - the
> AV7110 ARM seems to have an upper bitrate limit of 9Mbit/sec (happened
> to see someone mentioned that on vdr or linux-dvb list recently..), and
> this chip is present in many DVB-T STB's...

BBC ONE via Satellite has a stamped header of 7.98Mbit/s, and i'm pretty sure
its the same stream thats sent via DTT - so it'd make sense to be roughly
that.  As an example of a show, Top of the Pops on BBC1 is:

Videostream: ASPECT: 16:9  Size = 720x576  FRate: 25 fps  BRate: 7.98 Mbit/s
Audiostream: Layer: 2  BRate: 256 kb/s  Freq: 48.0 kHz

And a sample of the video mpeg stream for that clip:

    Computed avg rate : 513750 bytes/sec (4110000 bits/sec)
    Computed max rate : 907650 bytes/sec (7261200 bits/sec)

So should fit down the USB (just!)

Andy.

-- 
n: Andy Coates                         e: andy@bribed.net


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