[mythtv-users] ATSC Unwatchable

Keith Wait kwait at alumni.rice.edu
Sun Sep 9 20:47:28 UTC 2012

>> I did some more testing and you are correct; it is possible for me to
>> get signal values above 0xff.  I've gotten at most up to 1e0.  So yes,
>> I believe that what the linux PC is being fed is a lousy signal.
> I cannot imagine how that would be possible.  0x1e0 would translate to
> 48.0 dB, which is above the maximum the demodulator is capable of
> reporting.

Sorry, this was a typo.  I meant to write 10e (27.0 dB).  Since then,
I've seen signals up to 127 (29.5 dB), but really the signal questions
are just a distraction, as I will show shortly.

>> However, I don't agree with you that 'At this juncture all data points
>> to "crappy signal conditions".'  If that were the case, why (as
>> originally noted) does plugging the antenna directly into the TV next
>> to the PC (TV, PC, antenna all unmoved) give me clear picture?  And
>> why does the card in a windows PC located in roughly the same place in
>> the house work just as well as the TV?
> There indeed could be a driver problem, or the problem could be with
> the application.  One thing worth trying would be to run "azap -r
> CHANNELNAME" and then "cat /dev/dvb/adapter0/dvr0 > foo.mpg".  Then
> play the resulting foo.mpg in mplayer or VLC.  If it really was a
> signal problem, then the video would be corrupted there as well.  If
> it plays fine, then you've definitely got a problem with Myth.

I tried this and it gives me the garbage that both myth and mplayer
do.  So I guess we don't eliminate either the hardware or the driver
as a problem.  But, this morning I did the following:

1. Put in a mythbuntu livecd (8.04).
2. Installed dvb-apps.
3. Ran "scan us-ATSC-center-frequencies-8VSB | tee channels.conf"
This gives me pretty much the same channels.conf that I get running
from my hard drive.
4. Copied the channels.conf into .mplayer
5. Ran "mplayer dvb://CHANNEL_NAME -dumpstream" I believe this
accomplishes the same thing as your "cat /dev/dvb/adapter0/dvr0 >
6. Played the resulting stream.dump on a couple of different
computers.  Result: perfectly clear picture and sound.

So, based on my understanding, the only place that things can be going
wrong on my normal install is somewhere in kernel-land.  The userspace
utilities all agree that the picture is junk and the hardware is now
shown to work just fine.

If I must re-install to clear the problem, I will, but it's taken me a
long time to get the system set up the way I want it.  Since the only
outstanding issue is this one, I'm hoping that there is a way to
non-destructively fix it.

Here's an overview of my setup:
xbmcbuntu (based on oneiric), running kernel 3.0.0-22-xen-dom0 (so
running the xen hypervisor).
myth-backend is running as a service on the xbmcbuntu dom0, uses
mythbox add-on for xbmc to connect to the backend.
There's an openmediavault as a hvm underneath it with a harddrive
dedicated to the hvm.
Intel Sandybridge graphics over HDMI to my tv.
The capture card is an Hauppage HVR-1250 and is loaded with the dmesg result:

[    8.834849] Linux video capture interface: v2.00
[    8.874906] altera_stapl: module is from the staging directory, the
quality is unknown, you have been warned.
[    8.909064] cx23885 driver version 0.0.2 loaded
[    8.909107] xen: registering gsi 19 triggering 0 polarity 1
[    8.909110] xen_map_pirq_gsi: returning irq 19 for gsi 19
[    8.909112] xen: --> pirq=19 -> irq=19 (gsi=19)
[    8.909117] Already setup the GSI :19
[    8.909121] cx23885 0000:02:00.0: PCI INT A -> GSI 19 (level, low) -> IRQ 19
[    8.910120] CORE cx23885[0]: subsystem: 0070:7911, board: Hauppauge
WinTV-HVR1250 [card=3,autodetected]
[    9.037807] tveeprom 15-0050: Hauppauge model 79571, rev D6D9,
serial# 7896085
[    9.037811] tveeprom 15-0050: MAC address is 00:0d:fe:78:7c:15
[    9.037813] tveeprom 15-0050: tuner model is Microtune MT2131 (idx
139, type 4)
[    9.037816] tveeprom 15-0050: TV standards NTSC(M) ATSC/DVB Digital
(eeprom 0x88)
[    9.037818] tveeprom 15-0050: audio processor is CX23885 (idx 39)
[    9.037820] tveeprom 15-0050: decoder processor is CX23885 (idx 33)
[    9.037822] tveeprom 15-0050: has no radio
[    9.037824] cx23885[0]: hauppauge eeprom: model=79571
[    9.037826] cx23885_dvb_register() allocating 1 frontend(s)
[    9.037829] cx23885[0]: cx23885 based dvb card

Thanks again for all your help.

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