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Old 16th October 2016, 18:38   #1  |  Link
frankvw
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How to analyze non-compliant audio

I have a DVD which appears to be a private release (it's a German documentary with Dutch subtitles, no region or CSS as far as I can see) and I'm in the process of transferring all my DVDs to harddisk so that I can play them on a Rasperry Pi running Kodi.

When I play the DVD in my DVD player, I get background music on one channel (left) and the voiceover on the other (right). However when I copy the files to harddisk and play them (using VLC, Kodi, even Media Player) I don't get any voice-over, just the background music.

I tried to use Handbrake to convert the file to an MKV, including the Dutch subs) and the default audio codec there is AC3 (ffmpeg). I tried downmixing to stereo and mono, but no luck. I get either no voice-over or no sound at all.

Apparently there are come compliance issues here.

Incidentally, I've tried to use subrip to extract the Dutch subtitle track so I can translate it into English (my wife speaks neither German nor Dutch) but subrip won't even load any IFO or VOB files. Also, Kodi won't scrape the VIDEO_TS folder for this DVD. All indications of a non-compliant DVD.

How do I find out what the problem is? Is there something that will analyze this DVD (especially the audio track, but preferably everyting) and can provide some details as to what's going on?

Is this fixable?

// FvW
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Old 20th October 2016, 15:21   #2  |  Link
frankvw
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The plot thickens

Update: I have made some progress in analyzing the problem. When I play the audio track with VLC, I get the following results:

Stereo: Background music only
Left channel only: Background music with voice-over
Right channel only: Background music with voice-over
Reverse stereo: voice-over only.

WTF is going on here???

// FvW
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Old 23rd October 2016, 05:43   #3  |  Link
kuchikirukia
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non-complaint with what?
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Old 23rd October 2016, 10:37   #4  |  Link
tebasuna51
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Use PgcDemux to extract audio tracks and upload samples of them.
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Old 23rd October 2016, 13:04   #5  |  Link
frankvw
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Quote:
Originally Posted by kuchikirukia View Post
non-complaint with what?
Oh, I don't know... DVD format standards maybe?

// FvW
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Old 23rd October 2016, 13:06   #6  |  Link
frankvw
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Quote:
Originally Posted by tebasuna51 View Post
Use PgcDemux to extract audio tracks and upload samples of them.
Will do.

// FvW
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Old 23rd October 2016, 15:57   #7  |  Link
kuchikirukia
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Quote:
Originally Posted by frankvw View Post
Oh, I don't know... DVD format standards maybe?
What's the format?

And please don't spam with a signature.
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Old 24th October 2016, 07:49   #8  |  Link
hello_hello
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It sounds like the channels were mapped incorrectly when the audio was encoded and the only way to fix it would be to remap them correctly while decoding then re-encode.

If you have ffdshow installed and can decode via DirectShow you can use it's volume filter to listen to individual channels and it has a Mixer filter and a "swap channels" filter that can be used to swap them around. Once you have the correct channels in the correct places (left and right in left and right, centre in centre) etc. If you can decode via DirectShow when re-encoding ffdshow can remap the channels for you. There could also be empty channels that shouldn't be in which case you'd probably downmix as best as you can.

Or you can open the AC3 with Audacity, re-order the channels, change their panning and/or downmix etc and encode a new version. I'm pretty sure Audacity requires ffmpeg to open AC3 and it's particular about the ffmpeg version it'll use, but I think there's instructions on the Audacity site pointing to the correct version. Once open, you should see each channel displaying individually in Audacity. There's an example screenshot here.
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Old 24th October 2016, 10:20   #9  |  Link
frankvw
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Quote:
Originally Posted by kuchikirukia View Post
What's the format?
It's a ripped DVD, so I would assume it's AC3. I've got a VIDEO_TS folder with IFO, BUP and VOB files in it.

Quote:
Originally Posted by kuchikirukia View Post
And please don't spam with a signature.
Not sure what you're referring to. Spam? Where?

// FvW
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Old 24th October 2016, 10:27   #10  |  Link
frankvw
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Found it

OK. Following helpful advice from some posters in this forum, I managed to extract and demux the audio, then look at the wave forms on screen.

It turns out (I kid you not) that the audio started as a simple stereo track, with the background music on the left channel and the voice-over on the right (known as pingpong stereo in the days of Vinyl records) which was then, for no apparent reason, upmixed to DS5+1, BUT... because some channels are 180 degrees out of phase, either audio _or_ voiceover disappears when being downmixed back to stereo during playback.

Why? I have no idea. This DVD is definitely a private release, and whoever made it didn't do it too cleverly.

Thanks to everyone who helped me get this headache sorted out!!

I'm not in the process of straightening out the audio and will then remux it using MKVtoolnix or some such.

Tnx!!

// FvW
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