EAC3to 5.1 AC3 conversion to 6 mono wavs - sound goes out of sync with video

[Chug a Bug]

Hi I wonder if someone can help. I have a problem with a 5.1 AC3 soundtrack. The soundtrack only actually contains 2 channels - front left and right. The rest of the channels are empty/null/silent.

My question is: is there some way to downmix to the 2 channel audio without losing sound quality? EAC3to only contains a Dolby Pro Logic II stereo downmix option to my knowledge.

I can decode to to six mono WAV tracks using EAC3to and re-encode the two relevant tracks but the sound goes out of sync with the video which is quite noticeable after 2 hours. The audio appears to be speeding up. The command line is:

EAC3to soundfile.ac3 soundout.wavs

Video is 1080i, 29.97 fps.

I've tried using BeSweet to convert to six mono WAV files, which it does do - but the sound quality suffers. The sound does stay in sync this time however.

My question is: is there any way of downmixing 5.1 DD to stereo without re-encoding, or if not, at least without losing considerable sound quality? Thanks.

[tebasuna51]

Hi I wonder if someone can help. I have a problem with a 5.1 AC3 soundtrack. The soundtrack only actually contains 2 channels - front left and right. The rest of the channels are empty/null/silent.
Is strange. Can you use DelayCut to fix the original ac3 and see if there are any problem? Report the log file.

My question is: is there some way to downmix to the 2 channel audio without losing sound quality? EAC3to only contains a Dolby Pro Logic II stereo downmix option to my knowledge.
A dpl II downmix with channels C, LFE, SL, SR empty/silent produce the same output than a stereo downmix: the FL, FR channels attenuated but equal to originals.

I can decode to to six mono WAV tracks using EAC3to and re-encode the two relevant tracks but the sound goes out of sync with the video which is quite noticeable after 2 hours. The audio appears to be speeding up.
Maybe there are corrupted frames and the output is short (speeding up) than input. See the DelayCut log.

I've tried using BeSweet to convert to six mono WAV files, which it does do - but the sound quality suffers. The sound does stay in sync this time however.
The sound quality suffers? If you can listen easily different quality only can be because there are corrupted frames.

My question is: is there any way of downmixing 5.1 DD to stereo without re-encoding, or if not, at least without losing considerable sound quality?
Without re-encoding is not possible.

[Chug a Bug]

Is strange. Can you use DelayCut to fix the original ac3 and see if there are any problem? Report the log file.

Already done that and yes, there were errors. I used DelayCut to silence the errors then fed it through EAC3to to obtain a nice clean AC3 file. It's the only way the PS3 would play it. Tested it by feeding it through DelayCut again. No errors, a nice clean track. Then I remuxed it with video and everything is fine, no de-syncing. It's only after I separate it into mono WAV's with EAC3to that the trouble starts.

The audio is definately only 2 channels its from an HDTV source, they advertise Dolby 5.1 broadcast, which it is, but they only mix in 2 channels. Sneaky, huh?

Maybe there are corrupted frames and the output is short (speeding up) than input. See the DelayCut log.

No, see above.

The sound quality suffers? If you can listen easily different quality only can be because there are corrupted frames.

No, it's definately not as good. The volume has changed at any rate. EAC3to produces very nice WAV files with no sound deterioration, but it gradually speeds up & goes out of sync. I've tried applying PAL slowdown but that was a disaster. Way too slow.

Without re-encoding is not possible.

I thought not. Thanks anyway.

There is a problem with EAC3to IMHO. Maybe I should have posted this in that thread.