[mythtv] Recording multiple channels on a single DVB transport

Daniel Kristjansson danielk at cuymedia.net
Tue Dec 20 10:14:50 EST 2005

On Tue, 2005-12-20 at 14:52 +0000, Stuart Morgan wrote:
> =Recording multiple channels on a single DVB transport=
> First off, Yes I know this topic has come up quite often before. I'm 
> interested to know what hurdles stand in the current Myth code, especially 
> after all the DVB and general changes made in the last few months.
> I there would need to be changes to scheduling code but what about the 
> recording code? Is Myth even capable in it's current form or is it built 
> around the concept of one recording per tuner?
The TVRec is built around one-recording per tuner.
But this is still possible.

To make a DTV recording we go through a few steps
 1 close any existing access to DVB/HDTV file devices
 2 open a signal monitor and wait for it to find our channel
 3 open a recorder to record the program
 4 wait for recording to end
 5 close the recorder

The TVRec states all center around a single recording so I wouldn't
change that. But you can create multiple TVRec's per device but tell
them that they share a single tuner.

When someone wants to make a recording (the scheduler or the user)
and it is on a TVRec with a shared tuner you check if the tuner is
already in use. If it isn't you proceed normally. If not, then
assuming the channel is on the same transport/frequency you skip
step 1, and in place of step 2 you just check the PSIP/SI tables
for your channel. For step 3 you share the file descriptor for the
recorders, and instead of just closing the recorder in step 5 you
need to reference count the file descriptor and only close it if
you are the last one out (because recordings may end at different

The DVB recorder requires an additional change to filter only the
PIDS it should be recording, the HDTV recorder already handles this.

The only real changes for when this topic has come up before is
steps 1 and 2. So read up on those earlier discussions.

-- Daniel

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