Tuesday, 4 June 2013

MythTV and Recording from a SkyHD box.

At the moment my setup is as follows, a MythTV box runing Ubuntu Linux 11, with to Hauppauge Nova-S Plus S1 PCI Satellite cards. and 2TB of space.

It records (Mostly in SD since the BBC swapped to the S2 standard) quite happily day to day but I like to record the F1 to watch in the off season, so since this moved to Sky (boo hiss!!!) I need a way to get the recordings from the Sky box and on to MythTV.

3 Options present themselves

Option 1

Use Compisite out on the SkyHD box to the Composite in on one of Nova-S cards.
Downsides:Poor Quality

Option 2

open the SkyHD box take out the hard drive, nab the encrypted gp file, decrypt and ta da
Upsides:Free, HD

Option 3

use a HDMI in type recording device
Upsides:Easy, HD
Downsides:Not free, what if Sky switch on the HDCP encryption?

To begin with I'll go with Option 1 and see what the quality is like:
Capture over composite from SkyHD box.
Capture Via Composite from Sky HD Box
Not bad, watchable. But this is where i start to run into problems with sound. While the picture works a treat /dev/video0 there is no sound. Debugging the sound was a total pain in the whatsists and this blog entry is really here so I have somewhere to log the steps I went through.

Step 1, list all the audio in devices:

maff@mythbox:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC889 Analog [ALC889 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 2: ALC889 Analog [ALC889 Analog]
  Subdevices: 2/2
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
card 2: CX8801 [Conexant CX8801], device 0: CX88 Digital [CX88 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 3: CX8801_1 [Conexant CX8801], device 0: CX88 Digital [CX88 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

And this is where the fun and games begins, you can see the two sat cards CX8801 and CX8801_1. CX8801 is always /dev/video0 and CX8801_1 /dev/video1 however some times, say every other boot, the sound in is HW:2,0 and some times HW:3,0. Weird. Ok how about I plug the sound into mic in on the PC, thats unlikely to change. HW:0,0

To test this, a quick arecord remembering to specify sample rate of 48000 as this is what MythTV needs:

arecord -D hw:0,0 -r 48000 -f S16_LE -c2 foobar.wav

and play it back:
vlc foobar.wav


excellent, so back the mythtv-setup bash in hw:0,0 in the card config, save back to mythtv and....



so whats the difference, arecord can get audio from hw:0,0 but not mythtv, turns out Mythtv needs an ALSA prefix in order to work so should be set to ALSA:hw:0,0 and finally sound!

Awesome, hopefully next time it craps out and goes silent I'll now have somewhere to look and find out what I did.

1 comment:

  1. As you have paid to recieve the content, through your Sky Subscription, why not just torrent the coverage from thebox.bz. You will then have the HD file very easily and for free, with (IMO) a guilt free conscience.