[mythtv-users] Overlapping recordings on SAME channel w/ one tuner

Daniel Kristjansson danielk at cuymedia.net
Fri Apr 2 02:22:51 UTC 2010


On Sat, 2010-03-27 at 18:59 +0000, Andre wrote:
> I haven't yet looked in the multirec code yet but it seems to me that
> multirec already has the necessary capability to achieve overlap recordings
> on analog tuners.

Multirec for DVB/HDHomeRun relies on three things:
 1. The scheduler is aware that a that two or more cards can record
    at the same time but they must be recording the same channel
 2. The DVB/HDHomeRun recorder has a level of indirection thought an
    MPEGStreamHandler instead of interacting directly with the stream.
 3. The format of the recording allows you to start writing it to disk
    midstream and still have a valid recording (MPEG-TS).

All three were true for some time for the HDHomeRun, but it still
took a couple releases before the someone ported the DVB multirec code
to work with the HDHomerRun. For IEEE-1394 recorders 1&2&3 are true
and it only take about a week work to extend multirec to it (but all
you would get out of it is overlapping recording support). For most
cards using the v4l2 drivers only 1 is true. For the cards using the
ivtv and hdpvr drivers only 1 and 3 are true.

To support v4l2 frame grabber cards with multirec you would need to
rewrite the recording class from scratch to output something like
MPEG-TS instead of a NUV and add the level of indirection needed to
support virtual cards (there are other ways but they aren't any less
involved). For v4l2 there is more work involved than the whole DVB
multirec effort involved. The only reason I see to work on this is
if an affordable HDTV frame-grabber releases GPL'ed v4l2 drivers.

To support ivtv and hdpvr you would need to add the level of
indirection, and each one is a separate case just like DVB and
HDHomeRun based recorders were separate cases. This is more
doable but the payoff is small for the amount of work involved
compared to many other things on the my or Janne's plate. Of
course, if someone else does the work I could carve some time
out of my schedule to review the code.

-- Daniel



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