[mythtv-users] A little help clarifying dummy tuners and HD ringbuffers

[Cody Hofstetter]

After a very long weekend, here is the write-up recap of a couple errors
and how I fixed them:

"JumptoProgram's OpenFile Failed"
"E CoreContext fileringbuffer.cpp:300 (OpenFile)
FileRingBuf(/var/lib/mythtv/livetv/1043_20150805170925.mpg): OpenFile():
File too small (0B)"
"Error opening jump program file buffer".
These three errors were for the most part coming up together.

Note: Had already updated HDHomerun Prime firmware to latest version
available so assumed that wasn't an issue.

1) Removed and re-added tuners - didn't work

2) Increased HD Ringbuffer size - didn't work.
    2a) I did however find out a couple things about the HD Ringbuffer. HD
Ringbuffer max is set to 94Mb. I don't know why there is a max on this? Is
it not useful to increase above a certain threshold? Is the max leftover
from when boxes didn't have as much memory? Only indication of a possible
problem I could find increasing this was related to swapping.
    2b) The ringbuffer used to be re-assigned on a per channel basis from
what I gathered reading older posts. However, my assumption is this is no
longer true in MythTV because my logs indicated that the ringbuffer was
already running when switching channels and it didn't start a new thread
(it instead added to the one already running). This is purely my assumption
based on my logs. If someone (user or dev) can clarify exactly how the
ringbuffer works, feel free to do so if you are inclined so we can all
learn some more.

3) Tried learning about dummy tuners after seeing what I perceived as a
possible error - Long story short, not an issue
    3a) The perceived "error" looked something like DUMMY: 8004 (15:22:06
to 15:22:15) HDHomerun: 8004 (15:22:15 to 15:22:36) discontinuous. The
HDHomerun is not the only tuner card that uses these dummy tuners in this
way and so I don't think this is likely to be a cause of issues.
    3b) There are actually dummy tuners (now called Demo tuners) in MythTV.
These were originally designed for use on devices such as laptops to
emulate a tuner in software so a dev could work on an issue and contribute
without having the actual hardware. These also can be used in advanced
setups for backends which have no tuners but might need to emulate one to
work properly.

4) Increased the signal and tuning timeouts of the Prime - After this set
and step 5 I could consistently open and view some of the LiveTV channels.

5) Changed the quick tuning setting for Prime to "Always" because I thought
maybe there was a partial lock problem. Read the link mentioned eariler if
anyone wants a bit more info on the quick tuning setting. I don't think the
current description in Myth accurately describes it. I'll quote the part I
found most useful:
"It sounds as if mythtv gets confused when NOT quick-tuning if the
station doesn't
provide full stream information. Quick-tuning doesn't care about the stream
info, therefore it gives a workaround for missing info. This works well so
long as you don't have two channels with the same callsign. I think perhaps
we might want a "Only when necessary" option for "Quick Tuning", rather
than "Always" or "Never" there."

6) Navigated to the Prime's HTML logs. Everything looked fine. Navigated to
channel lineup. Here is where I found the issue. I noticed the Prime had
two of the channels I couldn't tune as DRM channels even though the
information provided by the cable company said they weren't. Boom, used the
channel editor to remove them and everything fired up perfectly. So long
story short, no DRM channels! Check even if the cable company says they
aren't.


Bonus error fix:
"Failed to initialize multiplex options" and "unknown tuner type =0x2000"
I'm quite new to Myth and was receiving this error when originally trying
to set up the Prime for LiveTV. After searching I couldn't find the answer
and turned to the mailing list. Note this Prime is being used with a
CableCard.

As Gary Buhrmaster pointed out to me:
"It sounds like you are not using the Prime as a CableCARD device, but
instead are trying to use it as a clear QAM device (EIT does not work with
Cable Systems, you have to investigate Schedules Direct). You cannot scan
for channels with a CableCARD device (well, at least MythTV has no support
for accessing the various OCUR facilities to access the CableCARD channel
information)."

He was right. I assumed the channel information was able to be pulled
because the CableCard would help decrypt everything (including the channel
info). I was wrong in this assumption and so if you are having this
multiplex error, check to make sure you aren't trying to pull EIT info
while using it as CableCard device.

Thanks again everyone! Hope this quick write-up helps someone solve a
problem in the future. Started talking to Peter about the wiki so got that
answered too.
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