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MythTV + NTSC + faster machine = impossible?
PostPosted: Sat Jan 19, 2008 10:44 am Reply with quote
kshots
 
Joined: 13 Jan 2008
Posts: 16
Location: Florida




Hello all - I've just recently decided that using my Via mythtv frontend as a backend with this card isn't all that great an idea - I can usually do recordings on NTSC via S-Video with the audio going into my sound card, but it can't play back while it's either transcoding or recording (too much work for the little guy).

So, I've temporarily moved my backend to my desktop, an Athlong64 X2 4400+... and haven't had the thing working properly since.

I started by mimicking the settings I had used on the Via machine - I moved my tuner box over to my desktop and hooked S-Video up to the 5500, and the audio went to my X-Mystique line-in. I used the Analog V4L capture card setting in mythtv-setup to find the card (as I did on the via machine) and pointed the audio device to /dev/dsp (my X-Mystique). Fired up the backend, told my mixer for the X-Mystique to capture from line-in and muted the line-in output (mythtv replays from a recorded stream at all times, live audio would be out-of-sync), and fired up the front-end in the other room.

Eww.... lots and lots of static in the audio. The audio was there, and it was synced, but it was horrible. Played with mixer settings, but no matter what I muted, raised the level on, or lowered the level on, nothing changed the static.

Ok, so step 2 - try another sound card. My nForce4 has an AC-97 intel audio card built-in, so I recompiled the kernel with an intel-8x0 audio module, enabled it in the kernel, set it to the 2nd index via /etc/modules.d/alsa (and ran update-modules), modprobed it, and pointed the audio device to /dev/dsp2. This way my main sound card is 100% out of the loop. Tried another recording... and the static was 10x worse.

Hrmm... step 3 - drop s-video and go with coax (cable) with audio on the same line and use the HD-5500 as the sound card. This had partial success... the first few seconds get crystal clear audio, then it gets worse and worse, the video pauses and goes in fast forward every second or so, and the recordings are absolutely horrible. Sometimes it even crashes my backend. This time I'm also getting backend messages about audio buffer underruns.

What else can I try? I've tried other option under the mythtv-setup, including DVB DTV capture card (v3.x)[b] and [b]pcHDTV DTV capture card (w/V4L drivers)... both of which fail to get a signal lock on NTSC no matter what I try (in fact, I can't get them to attempt anything over NTSC - they insist on using ATSC, even with the analog options configured on the DVB DTV capture card (v3.x).

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Re: MythTV + NTSC + faster machine = impossible?
PostPosted: Sat Jan 19, 2008 9:42 pm Reply with quote
BGD
 
Joined: 18 Jan 2008
Posts: 8




Have you tried setting your sampling to 48000 while using the 5500 DSP device for audio capture? You also need to change the playback options for Live TV on your frontend(s) to 48000.

The only thing that is working on my Mythbuntu system is the V4L driver and it looks terrible. If I watch it live from xawtv or tvtime video looks great, but whatever Myth is doing leaves a lovely white line at the top of the frame. If I setup the cards as DVB w/ V4L driver I get the No Signal lock error you mentioned. Pretty frustrating Sad
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PostPosted: Sun Jan 20, 2008 2:00 pm Reply with quote
kshots
 
Joined: 13 Jan 2008
Posts: 16
Location: Florida




I've tried setting the rate limit from everything from 32000 to 48000... but I haven't tried setting it on the frontends yet. Not sure I really want to... if it's recording bad data, I don't particularly want to store it. The frontends are just playing back recorded videos.

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PostPosted: Tue Jan 22, 2008 7:52 pm Reply with quote
kshots
 
Joined: 13 Jan 2008
Posts: 16
Location: Florida




Ok, the solution to this was a bit... odd...

First, the main problem was that I was using ALSA instead of OSS to handle my audio on my frontend. Apparently, ALSA does not get along well with OSS with some sound cards (definately not with my main card, probably not with the cx-8800). Switching my front end to use OSS while my backend was also using OSS resolved the buffer underrun issues I was experiencing.

I suspect the reason for this is that either my sound card does not have a hardware mixer (common for non-creative sound cards under linux) or the cx-8800 does not have a hardware mixer. I don't know which is the real case.

Unfortunately, the audio still sounds REALLY weird... but that I could at least play around with.

Thus far, the best results I have is when I tell the HD-5500 to record at 48000 hz (as suggested here). I'm hoping (crossing my fingers) that when I also re-encode at 48000 Hz that it will become crystal clear.

EDIT: I also note (now that brighthouse has installed digital cable here and I'm off the satellite crap) that I can now define NTSC channels to scan under the DVB driver. Previously, if it didn't find any ATSC channels, it absolutely refused to do NTSC channels. This is now resolved in my case... but perhaps the mythtv folks ought to update their frontend?

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MythTV + NTSC + faster machine = impossible?
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