MVP, AC3 channel mapping issue

[richsoft]

Hi,

I am new to SageTV and I'm very impressed with it. I have it running on my Home Server, feeding two MVP extenders.

One of my MVPs is an old E1 version, and that is working fine over RGB SCART.

The other is a more modern wired H3 model, with a coax SPDIF out built in. This works fine, with the sound output via SCART and over the SPDIF (at the same time) which I have connected to a hardware decoder (and old Creative Exitigy).

The issue I am having is when the video being played on the H3 has an AC3 soundtrack; the speaker channels are mapped incorrectly over the SPDIF output.

If I play a DVD directly using SageTV, streaming it to the MVP the sound is fine, with the channels mapped correctly. (It actually sounds better than from my standalone DVD player plugged into Exitigy!).

Strangely if I rip the same DVD into an XVID avi file, keeping the AC3 sound track, the channels are wrong:

Centre Channel -> Left Speaker
Right Channel -> Centre Speaker
Rear Left -> Right Speaker
Rear Right -> Rear Left Speaker
LFE -> Real Right Speaker
The Left channel doesn’t play, so I guess it’s going to the sub woofer.

I have checked various files, encoded by different programs (always keeping the original AC3 audio), with the same results, so I don’t think it’s an issue with my encoding. If I play the files on the PC, the speakers are correct too.

As this weird mapping issue only occurs when playing a file that is transcoded for the MVP (if I play a DVD directly, the files do not need to be trancoded, and everything is fine), then I am wondering if I have something set up wrong.

Does the transcoder re-encode the AC3 track before sending it to the MVP, or does it just send the original data? Are there any settings in any of the .properties files that I can change to control the transcoder?

Thanks in advance,

Richard

[richsoft]

Sorry, to reply to my own posting...

I have been doing a bit of experimentation to find out what is happening.

It appears that the SageTVTranscoder.exe (which is run when viewing the Xvid on the MVP) is a version of FFmpeg, so I have looked up the command line parameters to it.

If I transcode the xvid from the command line:

SageTVTranscoder.exe -i "test.avi" -vcodec mpeg2video -acodec copy -target dvd "test.mpg"

I get a file which the MVP will play directly. It still has its AC3 audio track, and the channels are mapped to the correct speakers!

The file will play on my H3, both to the TV over SCART, and over SPDIF to the Extigy where it is decoded correctly. It also plays on the E1 over SCART without a problem. I'm not sure if its downmixed to 2 channels, or you just get the front left and right channels, but it sounds OK either way.

This suggests that there is a problem with the way that the transcoder normally converts the file for the MVP.

It must be reencoding the AC3 track again, which messes up the channels.

I will keep investigating...

[Taddeusz]

Originally Posted by richsoft

This suggests that there is a problem with the way that the transcoder normally converts the file for the MVP.

From my understanding if any part of a media file needs transcoding for playback the entire thing gets transcoded. Even if part of it does not. This is rather unfortunate but just the way SageTV works.

If you would like to sway SageTV to do otherwise you could try making a suggestion to them directly as this is stricly a user-to-user forum.

[KipKasper]

I have this exact problem with my MVP
DVDs play fine
anything that needs the transcode service has mixed up channels.

My MVP is Model '83019 - H3'
and I am using the coax Audio out to my receiver.

Help!
- Greg

[richsoft]

I've done some more investiagtion, and have found the answer to the problem (at least for me )


* Stop the SageTV service

sage.properties file in c:\program files\sagetv\sagetv

* Scroll down to find the line that look something like:

media_server/transcode_quality/DVD6Ch=-f dvd -b 4000 -s 720x576 -acodec ac3 -r 25 -ab 384 -ar 48000 -ac 6

* Add a new line:

media_server/transcode_quality/DVD6ChAC3=-f dvd -b 4000 -s 720x576 -acodec copy

ClientMACAddress.properties file in c:\program files\sagetv\sagetv\clients

* Scroll down to find this line:

miniclient/transcode_mode_6ch=DVD6Ch

* Change it to use the new profile you added to the sage.properties file:

miniclient/transcode_mode_6ch=DVD6ChAC3

* Start the SageTV service again


This causes the transcoder to just directly copy the sound data from the file, if it detects 6 channel sound.

This works for me with normal DVDs and DVDs I have ripped into Xvid with the AC3 audio. The channels are all in the correct place in both

It is likely that this will stop the MVP playing things that have 6 channel sound in something other than AC3 format, but I havent tested this yet...

I hope this helps...

Cheers

Richard

[lombruan]

Hey Richard

Have you tested it with other things that have 6 channel sound in something other than AC3 format yet?

I did add the lines you said, but to no avail. Back to square one for me...