Linux QAM256 works / QAM64 does not... on Tvheadend 3.4 and HDHomerun HDHR3-4DC
#1
Exclamation 
I have a HDHomeRun HDHR3-4DC and a server with Ubuntu minimal installation running Tvheadend 3.4. Tvheadend succesfully recognizes 4 tuners and can use these tuners to discover muxes and services. I can watch these services using VLC Media Player straight from the Tvheadend web interface. Finally, scrambled channels are successfully unscrambled using a softcam (OSCam with SmargoV2). That was the good news.

The bad news is that I am missing a bunch of services. Tvheadend reports 30 muxes and about 300 services. On closer inspection I notice that 6 of these muxes have no detailed information, whereas all the other muxes have full information (description; id; etc). Trying to play a stream from these muxes using VLC leads to no result. A quick google through some online mux-service-channel listings tells me that the services which I am missing are a part of my non-functioning muxes.

There is one obvious thing that sets the non-functioning muxes apart, from the functioning muxes:
  • All functioning muxes are on QAM256
  • All non-functioning muxes are on QAM64


Inspecting the output from TVHeadend while viewing channels through VLC-player tells me the following
  • Functioning channels show lock=qam256
  • Non-functioning channels show lock=none, while qam64 is expected

Using the hdhomerun linux command line tools, I was able to manually switch one of my tuners to the right channel. According to the output of hdhomerun, I got a fully functional stream using the same settings that TVHeadend should be using when tuning to a channel.

Apparently, something is causing TVHeadend to ignore the modulation of channels on QAM64.
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#2
Random thoughts...

Are the non-functioning muxes set to Auto modulation, or something else? Can you change them in the web interface?

Can you delete them and re-discover them?

Or add them manually with the known frequency and either
(a) as few parameters as possible, with everything you can set to "Auto", or
(b) as much information as possible, so you're specific about how it should be configured?

Do you get any different behaviour with later (3.5 or 3.9) versions of tvheadend (I appreciate you've a delicate system that probably took ages to set up and don't want to break, so maybe build and install a separate tvheadend instance, or even run off a portable OS)?
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#3
Thank you for reply and thank god that I am using virtual machines with snapshots. Upgrade to 3.5 made no difference. Upgrade to 3.9 was pretty bumpy. Plenty of package errors left and right.. but.. it works!

I will setup a fresh VM with 3.9 tomorrow and do a clean install of tvheadend from scratch. See how far I get this time :-)
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#4
Or not... Many hours and pulled hairs later this is where I am at:
* All channels on a QAM256 mux work fine. They are always found on initial scan and map flawlessly on the first attempt.
* All channels on a QAM64 never work initially. However, after hammering the stream button it picks it up after a while. Once the stream is up and running... it works flawlessly?

These signal strength ratings are from the tuner itself, streaming one of my problematic channels on a QAM64 mux:

Modulation Lock a8qam64-6875
Signal Strength 88% (-7.3 dBmV)
Signal Quality 100% (32.7 dB)
Symbol Quality 100%

Looks fine right?

This is what it looks like when TVHeadend does not work:

Virtual Channel none
Frequency 690.750 MHz
Program Number none
Modulation Lock none
Signal Strength 21% (-47.6 dBmV)
Signal Quality none
Symbol Quality none
Streaming Rate none
Resource Lock none

Tuner 0 Status
Virtual Channel none
Frequency 690.750 MHz
Program Number none
Modulation Lock none
Signal Strength 88% (-7.6 dBmV)
Signal Quality none
Symbol Quality none
Streaming Rate none
Resource Lock none

The modulation is not locked on anything. The signal strength rapidly jumps between 20% and 88%.

So, in VLC, I keep stopping and starting the stream. Then after 5 to 50 attempts.. It picks up and the stream is rock solid!

Tuner 0 Status
Virtual Channel none
Frequency 690.750 MHz
Program Number none
Modulation Lock a8qam64-6875
Signal Strength 88% (-7.8 dBmV)
Signal Quality 100% (31.9 dB)
Symbol Quality 100%
Streaming Rate 14.644 Mbps
Resource Lock none
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#5
Going to buy a Humax IHDR-5400C and see if a consumer grade decoder can handle the QAM64 streams.

To be continued...

UPDATE: QAM64 works fine on the decoder. I've upgraded the HDHomerun to the latest bleeding edge beta firmware. Made no difference. Then I started screwing around with the settings. I had the dvbc modulation set to a8qam64-6875 a8qam128-6875 a8qam64-6875 which is what everyone else in my country uses. The command was this:

hdhomerun_config **my device id** set /sys/dvbc_modulation "a8qam64-6875 a8qam128-6875 a8qam256-6875 "

This is the exact same thing that the Windows Setup does. Thinking, what the heck, I set all three options to QAM64

hdhomerun_config **my device id** set /sys/dvbc_modulation "a8qam64-6875 a8qam64-6875 a8qam64-6875"

Which didn't seem to have an effect. Then I tried

hdhomerun_config **my device id** set /sys/dvbc_modulation "a8qam64-6875"

..and.. BAM.. everything works fine. All channels are instantly accessible. Hell, even channel switching is faster. This makes absolutely no sense as these settings would mean I lose all QAM256 channels but this is not the case.

Weirdness...
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QAM256 works / QAM64 does not... on Tvheadend 3.4 and HDHomerun HDHR3-4DC0
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