I have a problem. On all four of my front ends, I have stereo audio output (I do have a $5 aureal vortex2 card coming in the mail that has coax so I can output digital from my master box to my receiver though). Anyhow, on any of those front ends, when I watch a show that has ac3 encoded audio (I'm running off of a DCT6200/firewire) like almost every movie on HBO, HD local channels, etc., the first time mythfrontend starts, the sound is normal, but after I change channels a couple of times, it seems like the rear surround channels get mapped to left and right, and nothing else comes out (I can only guess, though the only thing I hear is ambient sound, like engines, and when something loud happens off screen, I hear it there...oh, and faint echos of voice sometimes). It has to be a glitch in either ALSA or FFMPEG (or lib-mpeg which I use on my laptop) that causes it as it happens on 4 different systems with 3 different distros.

I know with ALSA you can map outputs to multiple channels, so you will hear stereo audio come out of all channels of your 5.1 set up if you wanted. Is it possible to reverse this so my audio will be consistant? What I mean is mapping FL/RL and center to the left channel, FR, RR, and center to the right channel. Has anyone gotten this working?

-Rich

wow yeah this has something to do with 2.1 vs 5.1 sound on stereo output. I had this problem about a year and a half ago, but I don't remember what the solution was not, as I have since moved to using spdif output. there may be some old threads hanging around about it.

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Xsecrets

X,

I searched for a while under your name (I've searched for hours on this subject) and couldn't find anything. Do you have any idea what you may have done?

I have a similar problem.

I have used ALSA route plugin to get the right sound on the right channel (tested by using Dolby Surround trailers and some other surround test movies in mplayer). First I just connected the right speakers to the right output (sound card has 6 channel output) but then I realised that the mixer did not adjust the right sound. For example if I set Subwoofer to zero the rear left speaker would get silent.

Now, when watching TV there is no surround (yet, as far as I have understood the frontend does not handle 5.1 sound yet), but I at least get sound from the front speakers as expected. BUT, if I skip forward, and also some other times, the sounds gets out on the wrong channels (I get it on subwoofer and center). I have to exit the recording (marking the position) and restart it to get the sound from the right speakers. Then it works as before, but if I do some skipping back or forth the sound gets wrong again and I have to exit and restart. It also sometimes gets wrong when myth skip commercials.

I'm not sure if this is ALSA-related or myth-related.

well here is a thread from the mailing list describing your problem. I can't seem to find my old threads from this forum, could have been some of the ones lost when the site got hacked, and I really can't remember what the solution was now.

unfortunately I don't think this thread really has a solution either.

http://www.gossamer-threads.com/lists/m ... io;#133661

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Xsecrets

weird... i had this problem watching CSI last night (which was advertised as being broadcast in "HD/5.1"). i'm just using an analog stereo out (a nice surround tuner is in the plans, but can't afford it yet). it seemed like the rear channels were being pumped out of my stereo L/R out. so i just got music and sound effects - no dialog at all.

i tried to watch the recording in xine, mplayer, and vlc and i got the same result. there only seems to be one audio track encoded on the recording.

so... is this a problem with my setup... or was the broadcast messed up tonight and they put the rear channels in the non-surround mix instead of the front. i'm not too familiar with how ATSC broadcasts sound and how mythtv and alsa decode it. can anyone point me to understandable documentation?

thanks!

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From my experience, I've encountered more screw-ups on the broadcast end than in KnoppMyth. I thought I had this problem at one point and it turned out the broadcaster was screwed up in the AC3 audio they were sending. That's happened to me several time (and even on CSI, coincidentally). I have not watched the season opener for CSI yet, so I can't say if your experience was a "national" screwup, a "local" (your station only), or a KM problem.

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I started having this problem (Rear channels up front, muted voice audio) out of the blue. It appears to only be some stations and newer recording which makes me think that it's a new way some stations around here are broadcasting. I just juggle my ALSA settings around until it works. I think now I'm on ALSA:default;default;passthrough is checked as well as AC3 and DTS.

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