[mythtv-users] Max number of DVB channels per usb tuner

[Mike Perkins]

On 21/12/13 11:40, Mark Perkins wrote:
> I was looking for something, don't remember what now, but came across the following statement on a site advertised as a complete guide to MythTV - http://www.techradar.com/news/software/applications/complete-guide-to-mythtv-947946/4
>
> ******
> If you're using DVB (either terrestrial or satellite), you're in luck,
> because these multiplex several channels into one stream. MythTV is able
>   to receive an entire stream from a DVB tuner card, and then split it
> into individual programmes.
> When adding a capture card in mythtv-setup, press the Recorder Options
> button to see a further screen, which includes a Max Recordings setting.
>   Three is a sensible setting for this, and means that you could record
> six channels at once if you have two capture cards.
> ******
>
> Is that statement correct - ie that the number of channels that can be tuned from a single multiplex is not a hardware "given" of the particular card / tuner (in a DVB context)?
>
> I've set mine to two per usb tuner but that was because I thought I remembered reading on the box (back when I had the box) that it was capable of two channels.
>
> I've gone back to the manufacturer website to see what it says but it only has the following statement which I am not sure whether it means that it can tune two multiplexes (on a single usb tuner) and two channels from each multiplex, or 4 channels from a single multiplex.
>
> ******
> Multiple Video Processing mode, enables two TV tuner devices, up to four
>   channel program processing simultaneously. You can simply upgrade your
> TV enjoyments with one more WinFast digital TV tuner card/ box for
> multiple TV viewing.
> ******
>
> No doubt there are other considerations (ie hardware of the backend) but I think USB 2.0 does 480Mbps and a multiplex is 20Mbps total so the USB part should be fine. I think a 7200rpm HDD can do around 60Mbps sustained write so that should be plenty as well.
>
Technically, the tuner is "tuning" a multiplex, since that is what happens to be 
transmitted on a particular frequency. Once tuned, the usual procedure is to 
filter out the one channel (multiplexed stream) the user wants from among those 
available.

Of course, since the whole multiplex is available, and the filtering is done in 
software, it is (relatively) easy to select and process as many channels as the 
user wants from that multiplex. That's what 'multirec' in myth can do.

-- 

Mike Perkins