[mythtv-users] AAC 5.1 decode and analog playback

Mark Fink marksfink at yahoo.com
Wed Nov 21 14:09:29 UTC 2007

Planning a MythTV HTPC build with...

Asus P5K-VM mobo that uses Intel ICH9 / Realtek ALC883 chipset supporting 8.1 audio. The board has analog outputs for multi-channel audio (front, center, rear, LFE). It also has a coax port for AC3 passthrough.  Plan on using Intel Core 2 Duo E6750 (for what its worth).

To the point...I want to backup my DVDs (that I have paid for) to H.264/AAC 5.1 mp4 files. I want to playback these files and still enjoy discrete 5.1 surround sound with no downmixing to stereo or DPL-II, and I have read volumes about this in forums.  And I think I have my solution, but am looking for a sanity check.

I have a Sony receiver that has RCA inputs for 5.1 audio that has already been decoded by another device. It also has a coax input for receiving an AC3 signal for the receiver to do the decoding. The receiver is connected to a 5.1 speaker arrangement.

Without having purchased or tried anything, I believe I have 2 realistic (in terms of time and effort) options:

1 - rip/transcode audio to AAC 5.1, then on playback, decode the AAC audio with software on the HTPC (with MythVideo or mplayer or xine, no strong preference), output the decoded multichannel sound out the Asus board to the 5.1 RCA inputs on the receiver.
2 - route AAC 5.1 audio through ac3filter which transcodes to AC3 on the fly and spits it out the coax S/PDIF to the receiver which then does the decoding.

Intuitively, to me at least, the first option would seem to be better because of fewer conversions.

I'm not into other solutions that involve muxing H.264/AC3 together into matroska or MPEG-TS because this appears to me to be complex and time-consuming.  Then again, I could just compress video with Divx or Xvid and maintain original AC3 audio, but would prefer to use H.264 as everyone universally agrees to its superior quality.

Am looking for educated opinions.  Thanks!

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