AC3 Downmixing Question (1 Viewer)


Portal Member
November 25, 2005
MediaPortal Version: 1.0
MediaPortal Skin: Titanium
Windows Version: XP
Sound Card: 24bit Soundblaster External Live!
Sound Card AC3:
Sound Card Driver:
MPEG2 Audio Codec: ffdshow

I have searched the threads and think I have come across a unique situation that I am hoping someone might be able to help with. I have a USB external 24bit Sound Blaster Live! connecting to my Onkyo receiver via SPDIF optical. From what I have read so far, I am not able to do true AC3 passthrough as the usb soundcard doesn't support true 5.1 out.

That being said, I have recently started backing up some of my cd's for easier access to x.264 and AC3 5.1. Now when I go to play them in MP, unfortunately I get no audio. If I play them in VLC, I get audio. Now according to VLC it is downmixing the audio to 2 channel. So I know my encoding is fine.

I have MP configured to use ffdshow. I have tried having it use MPA. I have tried having it use AC3filter, none of which have seemed to work. Coincidentally, the AC3 filter test fails in being able to send any AC3 data through.

Also, mounted ISO's play fine.

The only thing I can think of is the Soundblaster not being able to send AC3 passthrough on the SDPIF and that's where my hangup is. I would like to downmix this so that I don't have to go and reencode all these files especially since I plan on upgrading my HTPC within 6 months to a card that can support true AC3 7.1 passthrough.

Any suggestions on where I can look? The one thing I haven't tried because I wanted to avoid it was going the ffdshow mixer route. This seems to me that it will downmix everything and I don't want the to happen. My AC3 AAC files play great on my 5.1 and would hate to lose that.

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