So, I have these DVDs from a boxset that all have a 2.0 DTS track. Except one that shows up as 5.1. When inspecting the VOB file it looks like a proper stereo track, but MakeMKV, eac3to, mkvtoolnix, all produce a "fake" 5.1 track with a strange tag when seen with MediaInfo ("Channel(s)_Original") that suggests it's actually stereo. When opening said track with Audacity the first two channels have sound, the rest are empty. See the mediainfos below:
Original VOB from DVD
DTS extracted from the MakeMKV remuxCode:Audio #2 ID : 189 (0xBD)-137 (0x89) Format : DTS Format/Info : Digital Theater Systems Muxing mode : DVD-Video Duration : 17 min 16 s Bit rate mode : Constant Bit rate : 755 kb/s Channel(s) : 2 channels Channel layout : L R Sampling rate : 48.0 kHz Frame rate : 93.750 FPS (512 SPF) Bit depth : 16 bits Compression mode : Lossy Stream size : 93.2 MiB (9%)
It's impossible to use "-downStereo" with eac3to, I get this:Code:Audio #2 ID : 3 ID in the original source medium : 189 (0xBD)137 (0x89) Format : DTS Format/Info : Digital Theater Systems Codec ID : A_DTS Duration : 1 h 12 min Bit rate mode : Constant Bit rate : 755 kb/s Channel(s) : 6 channels Channel(s)_Original : 2 channels Channel layout : L R Sampling rate : 48.0 kHz Frame rate : 93.750 FPS (512 SPF) Bit depth : 16 bits Compression mode : Lossy Stream size : 391 MiB (9%) Title : Surround 5.1 Language : Japanese Default : No Forced : No Original source medium : DVD-Video
So far I can extract the "5.1" DTS as is, open it with Audacity, delete the empty channels and export that as FLAC. Ironically the 755 kbps DTS file goes down to a 415 kbps FLAC. Lol, it's an old movie with shit sound, there must be so little data that the fixed bitrate DTS is a waste. In fact, both channels in Audacity looked the same, it must be a mono track originally.Code:a03 Extracting audio track number 3... a03 Decoding with libDcaDec DTS Decoder... a03 Encoding FLAC with libFlac... a03 libDcaDec output changed from 6 channels, 48kHz to 2 channels, 48kHz. a03 Creating file "C:\lol.flac"... Aborted at file position 262144.
Aside that, what can you do in these cases of "fake" DTS tracks? How can you get rid of the empty channels?
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Old movies are stereo at best - most cases audio was considered unimportant (used to create mood or as dialogue with some "fill gap" music).
Of course you can convert DTS to 2.0 channel. Alternatively you could in theory create if not multichannel audio then at least artificially created room characteristic multichannel (see no point when you can do this in real life using AV amplifier embedded DSP).