Way OT: breakdown Dolby Surround file

Former user wrote on 5/18/2010, 12:19 PM
I don't know if anyone can point me the right direction but I hope so. I have an HD Mpeg file encoded with Dolby Surround (L<R<C<MONO Surround). We are having to move the file to a different playback box but this box wants a different bitrate (at least we think that is the problem). This file was created 10 years ago, so we only have a D5 HD tape with the Dolby audio as a source. Is there anyway for me to deconstruct the Dolby Surround file back to the 4 discrete files so I can re-encode to Dolby Surround with a higher bitrate Some software or something.

I know this is weird and maybe not possible, but if you have any ideas, I am open to them

Thanks
Dave T2

Comments

John_Cline wrote on 5/18/2010, 12:45 PM
One of these AC3 to Wave tools might help:

http://www.videohelp.com/tools?toolsearch=ac3+to+wav&Submit=Search&convert=&s=&orderby=Name&hits=50
Former user wrote on 5/18/2010, 1:25 PM
John,

Thanks for the link. I will check it out. But I did just talk to the editor who worked on the project originally and he said that we have an HD Cam tape that has the Dolby two tracks on the tape that will make up the surround tracks (by using phase and such, information above my paygrade) and that all we need to do is re-capture at whatever bitrate we need, even can use PCM. So I think I can work it out. Thanks again for taking the time. I did some searches before I posted but could only find Dolby Decoding via hardware for playback. Notthing to break down the stream.

Thanks,
Dave T2
John_Cline wrote on 5/18/2010, 1:56 PM
It sounds like the video is encoded using Dolby Pro Logic instead of Dolby Digital. Dolby Pro Logic is an older method by which you can encode surround sound on to a stereo audio track. I don't know of any software which can decode Dolby Pro Logic into its surround sound components. It appears that your stereo audio tracks from the tape are already encoded so just process them as a normal stereo file.
Rob Franks wrote on 5/18/2010, 2:34 PM
I also know of no REAL software solution to decoding prologic... but what I did do once was was play it back in a prologic receiver and record each channel in real time as WAV. It worked out well but it did take some time
R0cky wrote on 5/18/2010, 2:42 PM
This is also an issue for those of us with a surround microphone that records Pro Logic II on to the stereo track in the camera.

I have been searching high and low for a software decoder without any luck. Anyone out there know of one???? Minnetonka/Surcode looks like they may have one but it is big bucks.

I've concluded that what Rob said is the only way, play it back through a hardware decoder and rerecord it.

Rocky
Rob Franks wrote on 5/18/2010, 2:49 PM
I looked at surcode and upon some digging (I found no conclusive evidence either way) but I don't think it actually DEcodes prologic
Former user wrote on 5/18/2010, 3:02 PM
Yep, John, you are right. It is pro logic surround. Done about 10 years ago. So I should be good to go. Thanks for your help again and everyone else.

Dave T2
R0cky wrote on 5/18/2010, 3:12 PM
I just looked at the surcode webpage and they definitely say it is a decoder and there are some screenshots that show "decode" as a selection.

They also sell Holophone surround microphones on their site which need a way to decode also if you want to mix/edit so that implies that surcode works ($800 USD). Of course, you could just ask Minnetonka too....

Rocky
musicvid10 wrote on 5/18/2010, 8:30 PM
In its original version Dolby PL uses a relatively simple ((L+R)+(L-R)) matrix for the mono rear channel, IIRC.

Any method that will save the stereo tracks will save the "encoding," although it is not really that since Dolby PL works with analog sources. And any amp that will recognize Dolby PL will play all four channels, although the rear will not be very good compared to discrete surround we have today.

That's the long way of saying I'd just include the audio as it is, and not worry about trying to bring a modern surround experience to the reissue.
Former user wrote on 5/19/2010, 5:47 AM
Thanks for the advice. I was not trying to update the file to a modern technology. Originally, I could only find a Dolby AC3 encoded audio file and knew of no way to alter the bitrate without the elemental streams. It was only after casually mentioning this to another co-worker that I found out we have the original HDCam tape with the audio. I did not work on this project and assumed that the person who did no longer worked here.

But I am always learning, that is why TV is fun to me.

Dave T2