[mythtv-users] Strange error: NVR: Can't open video device: /dev/video0

[Matthew Watts]

I have the same problem. I am using a generic USB 2 capture device that uses 
the em28xx driver, it has no tuner just an S-Video and a composite input, 
which I have connected to my Sky box, audio is connected to the line in on 
my normal onboard sound.
I am using Ubuntu with the latest everything, as a fresh install last week.

Spent hours on this, with no luck but I have come up with a few interesting 
finds.

Firstly I can watch TV fine using TVTime which shows the device at least 
works.

When setting up channels in the backend setup I can run a scan and it will 
start finding 'channels' (I assume it thinks my device has a tuner and is 
changing the freq blindly and testing for a picture) - interestingly if I 
put my Sky Box on standby it stops finding channels and turning the Box back 
on results in the scanner finding channels again. I think this proves that 
the MythTv Backend is definably able to read the TV signal to some extent!

lsof run under your user account may not have sufficient privileges to show 
files in use by the mythtv user. Running it as root while the Watch Live TV 
black screen is showing gives the following output.

sudo lsof /dev/video0
COMMAND     PID   USER   FD   TYPE DEVICE SIZE NODE NAME
mythbacke 31140 mythtv   17u   CHR   81,0      8098 /dev/video0

So it seems that altough the backend is complaining it cannot access the 
device, it oddly already IS accessing it!
As a sanity check, running it after the frontend disconnects shows 
/dev/video0 is no longer in use.

After learning this I have really hit a brick wall and am well out of my 
depth! Any advice is much appreciated!