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When playing a BluRay movie on a PC (any OS, Mac/Win/Linux), I have some questions about audio output:

  1. When playing a BluRay disc on the PC using a BluRay player program, can it decode the multichannel (7.1) LPCM/ Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA soundtracks in their HD formats (ie, without downmixing to Dolby Digital or DTS or PCM) and output the audio directly to the soundcard's 7.1 line-level analog outputs?

  2. Is it possible to bitstream the the multichannel (7.1) LPCM/ Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA soundtracks in their HD formats (ie, without downmixing to Dolby Digital or DTS or PCM) over the HDMI output to a receiver when using a BluRay player program?

I'd kinda like to know. I'm contemplating building a home theater PC, and the above functionality is important. I'd prefer that #1 is possible, actually, because it would mean I wouldn't have to buy a receiver.

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3 Answers

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I just built a home movie theater PC, and ran into the same problem. Let me address your questions one at a time. First question:

When playing a BluRay disc on the PC using a BluRay player program, can it decode the multichannel (7.1) LPCM/ Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA soundtracks in their HD formats (ie, without downmixing to Dolby Digital or DTS or PCM) and output the audio directly to the soundcard's 7.1 line-level analog outputs?

What you're asking for depends on the sound card for the actual output. For the decoding, a very powerful method is to simply use ffdshow as the main codec, and use another media player (e.g. Media Player Classic) to playback the content.

Currently, support for the new Blu-ray specific audio formats (as well as the older - but still Blu-ray - formats) has been added in Beta 6 (see here for the changelog and download link).

To set it up, go to the ffdshow audio decoder settings. Navigate to the last option, the "Mixer" panel. Enable it, and set up your speaker configuration (yours would be 7-channel, and check LFE to enable the subwoofer).

Then, it should be outputted from the proper outputs on the sound-card. If they're just analogue jacks, you will need cable splicers to change them from the little headphone jacks (and you will probably need to amplify the signal).

Now, to address the second question:

Is it possible to bitstream the the multichannel (7.1) LPCM/ Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA soundtracks in their HD formats (ie, without downmixing to Dolby Digital or DTS or PCM) over the HDMI output to a receiver when using a BluRay player program?

Well, continuing on with the ffdshow audio configuration, yes. You first need to set the HDMI as your primary audio output in your operating system. Then, navigate to the "Output" setting in the ffdshow config (just under "Mixer").

From there, you can check which signals you would like to pass-through unfiltered (e.g. AC3, DTS), your supported output sampling format (usually 16-bit), and the supported output formats if you want ffdshow to decode the stream (e.g. if you had a reciever that didn't support AAC, you could decode it and encode it to AC3 on the fly) or for formats which aren't supported by many recievers (e.g. raw MP3 data).

You have to note that it is a Blu-ray requirement that specific audio codecs are present on a disc, and that it is optional to have the newer formats.

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What you've described in this question applies to DVD, not BluRay, near as I can tell. AC3/DTS is a DVD format, not a BluRay format. Further, looking at the ffdshow page indicates that it focuses more on DivX/XviD/MPEG4. Not bad things, but not BluRay support. Couldn't find any documentation indicating that it could output BluRay formats. –  J. Polfer Sep 14 '09 at 13:09
    
Sheepsimulator... MPEG4 is the video format used by many Blu-ray disc's - which ffdshow can decode. Media Player Classic will use any MPEG2/4 video decoder it has available. Focusing on the audio side, which is what your question actually entails, it can handle decoding the Blu-ray audio formats, and if it your reciever handles it, then you can enable straight pass-through. –  Breakthrough Sep 14 '09 at 19:26
    
It can decode multichannel (7.1) LPCM/ Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA? Can you cite, within manual/source code/posts that ffdshow can do this? –  J. Polfer Sep 15 '09 at 13:46
    
Tried running the actual ffdshow installer. Current codecs supported: MP2, MP3, AC3(DD), AAC, DTS. These are DVD playing codecs, not / Dolby Digital Plus / Dolby TrueHD / DTS-HD / DTS-HDMA. –  J. Polfer Sep 15 '09 at 13:53
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ffdshow-tryout.sourceforge.net/changelog.php - "Beta 6 has been released... Support for E-AC3, DTS-HD, Dolby TrueHD". Just a note, E-AC3 is the same thing as Dolby Digital Plus (see the linked page at the top for details). –  Breakthrough Sep 15 '09 at 14:24
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According to this page, I guess it simply isn't possible unless a vendor develops a PAP pipeline in the PC software/hardware, and I think that would be very hard to achieve, especially considering how easily movie discs have been hacked in the past. So my guess is, either someone will have to crack the encryption scheme, or it just isn't possible with a PC. I look forward to reading other answers on the subject from those better versed in this than I.

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It really depends on the program you are using to play Blu-Ray. As far as I know, ArcSoft's TotalMedia Theatre supports lossless 7.1 channel audio output.

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A friend of mine uses this software on his HTPC setup, and 7.1 output is working from his Asus Xonar D2 sound card.

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So, with this setup, I guess the answer is yes, you can do all the things you wanted to do in your option 1.

EDIT : Found a sound card that appears to fully support Option #1.

The Auzentech HomeTheatre HD (review on Anandtech).

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I think you meant to say that this can do everything in Option #2, not option #1. The card doesn't decode TrueHD / DTS-HD or DTS-HD-MA. –  J. Polfer Sep 9 '09 at 13:34
    
Okay updated my answer : Found another card, the Auzentech HomeTheatre HD that will do TrueHD, DTS-HD and DTS-HD-MA. :P –  caliban Sep 9 '09 at 14:02
    
That still doesn't implement Option #1, but it fully implements option #2. The Auzentech card doesn't actually decode TrueHD, DTS-HD or DTS-HD-MA, it bitstreams the data over HDMI. –  J. Polfer Sep 9 '09 at 15:13
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