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More => Old Versions => Media Center 17 => Topic started by: tlum on February 21, 2012, 10:39:58 pm

Title: S/PDIF Passthrough, how?
Post by: tlum on February 21, 2012, 10:39:58 pm
Ok, so I just downloaded MC17, have been using 14. Quickly imported backup of default library from 14 into 17. And, of course none of the AC3 or DTS tracks play properly. They all seem to get decoded and converted to some kind of PCM before being sent over s/pdif no matter what I do. I never see FFDSHOW try to start.

So, what do I have to do to make this version work? These are AC3 and DTS tracks. FFDSHOW is installed and configured. The s/pdif card is an M-Audio Delta DiO which is a digital I/O card that sends s/pdif optical to the receiver. The receiver decodes AC3 and DTS. The computer is running Win 7 64 bit. MC14 is still working correctly.

The card has an ASIO driver but when I enable it MC complains that the card only supports 4 channels... which indicates that ts trying to send multichannel pcm which is totally wrong, I'm trying to do native pass-through.

I've tried Direct Show but again its trying to send multichannel pcm and ends up sending stereo pcm.

Is it any wonder I don't bother upgrading?

Title: Re: S/PDIF Passthrough, how?
Post by: BryanC on February 21, 2012, 10:53:03 pm
Tools > Options > Video > Bitstream: Set to SPDIF

You don't need ffdshow installed, MC has its own filters.
Title: Re: S/PDIF Passthrough, how?
Post by: tlum on February 21, 2012, 11:05:29 pm
Oh that's obvious; why would audio dependent option be under Video?

Works fine though!
Title: Re: S/PDIF Passthrough, how?
Post by: glynor on February 22, 2012, 01:10:39 am
Oh that's obvious; why would audio dependent option be under Video?

Because it only applies to audio tracks embedded in a video file.  It is part of the "video audio engine" (Red October) of MC, not the regular audio path for music.

ProTip:  The Options dialog has a search box.  It is handy.
Title: Re: S/PDIF Passthrough, how?
Post by: kdwoodrow on February 22, 2012, 12:37:16 pm
This is a helpful thread.  By way of background, I'm currently outputting sound via S/PDIF from my HTPC, but will eventually upgrade to HDMI when I upgrade my receiver to one that can decode HD audio.

One question: all of my MKV rips include two audio streams -- HD audio and DTS/DD -- so how do I select which one plays when I launch a movie?

Thanks!
Title: Re: S/PDIF Passthrough, how?
Post by: BryanC on February 22, 2012, 02:46:10 pm
I believe MC will choose the highest quality stream first. If you want to change it, right-click the screen while playing the movie, and change the audio stream selection.
Title: Re: S/PDIF Passthrough, how?
Post by: tlum on February 29, 2012, 07:27:42 pm
Actually, audio data (AC3, DTS, LPCM, etc.) and video data (MPEG-2, MPEG-4, etc.) are embedded in a container (.ts, .ps, .m2ts, .vob, .avi, .mkv, etc.). There is no such thing as a video file. It is the case that you'll rarely find a container with video streams that does not also have audio streams - since silent video is unusual - but containers with audio only is very common, especially in the case of encoded multi-channel audio. Its conceivable that there would be different engines that handle unencoded audio data - like LPCM - and encoded audio data - like AC3 - but the fact that stream handling is split between engines and one is called audio and the other video is an architecture that is not intuitively obvious.
Title: Re: S/PDIF Passthrough, how?
Post by: glynor on February 29, 2012, 08:08:21 pm
I believe MC will choose the highest quality stream first. If you want to change it, right-click the screen while playing the movie, and change the audio stream selection.

Correct.  It almost always picks the "right" thing to bitstream or decode for me, so long as it picks the right language.  There's a hierarchy.  I think it is something like: FLAC or Multi-Channel PCM > DTS-MA > Dolby TrueHD > DTS > Dolby Digital > everything else, but your language comes "first" if they're labeled.

You can also change it with the On Screen Menu during playback.  Use the Up/Down arrows during full-screen playback to choose from all the different OSD menus.  One of them (near the "bottom" of the "stack" so I think it is best to go "up" first) lets you select from the different audio streams.  You can also choose from the different subtitles in there (and maybe even different video streams in MKVs or something, but I don't have any of those to try).