[Request] NEAR DARK NTSC audio

[pipefan413]

Awesome!

Never mind adding the DTS to the BD if it doesn't fit.

Most people will be happy with the mkv with all the correct tracks if they want it all!

You finally saved that film.

Guess what?

The DTS JUST BARELY fits on a BD-25.

I'm very pleased.

[pipefan413]

I finally managed to get the BD-25 image working properly, so I reckon this is done and ready to go now. Turns out it was because tsMuxeR's default settings were messing with the timing info already in the video track, I just couldn't work out why. After muxing directly from the separate streams (rather than MKV) and switching off settings to insert SEI/VUI data and SPS/PPS (since those should be in the H.264 stream already, having come from a Blu-ray in the first place) it's sorted.

Also: I wanted to improve the accuracy of sync across all tracks, because it turned out the DVD had a 35 millisecond (probably imperceptible, though I guess possibly not) sync variance between the tracks. Originally I just tried to cut them all by the same timestamps, but I learned a bit about how audio sampling works, and how eac3to and various encoders handle it, which made me realise that I wasn't cutting as accurately as I expected to begin with and that I could potentially fix that to a certain extent.

I had come into this with the perhaps simplistic notion that I could simply cut audio at precisely the moment (to the millisecond) I wanted. This isn't the case: a bit like with video, which can only be cut at keyframes if you want it to decode properly afterwards, audio can only be cut at whole frames. The duration of said frame is determined by things like sample rate (48 kHz for DVD/BD) and codec. For instance, a 48 kHz frame of Dolby AC-3 lasts 32 ms. This probably goes some way to explaining why the DVD has a 35 ms difference (a little bit less than 1 frame of video at 23.976 fps) between where it syncs the DTS 5.1 track and the Dolby 5.1 track. In addition to this, because of cropping off old versions of the StudioCanal logo music and then sticking the newest version onto every audio track, I was introducing an additional error margin (because now not only was there a margin of error for the crop for sync, but also another amount of error caused by trimming the SC logo audio down to whatever whole frame cutting point was relevant for each codec I was using in each case).

So, rather than doing what I did to begin with and picking any one of the DVD tracks and using that reference point to sync all other DVD tracks against one of the audio tracks from the source French BD I used for the video, I instead synced each DVD track as accurately as possible. This involved paying attention to the actual cut points (rather than my intended ones), which was doable since eac3to logs how much of an error it was unable to correct for (e.g. if I asked it to trim off 16.653 seconds but the nearest whole frame was at 16.650 seconds, it told me "a remaining delay of -3ms could not be fixed"). I then tried to counterbalance this when cropping the 2018 SC logo audio I was going to append to the start, depending on how far it was out by. If when trimming the old SC logo audio off eac3to told me that it had left an extra 3 ms in the main audio, then I'd aim to trim off an extra 3 ms from the new SC logo audio being stuck on the start. Again, this wasn't possible to do 100% accurately, but I still got it a lot closer than the DVD.

The end result of this is that instead of having a difference of 35 milliseconds between the earliest (DTS 5.1) and the latest (Dolby 5.1) audio tracks like the DVD does, this remux instead has only an 8 millisecond difference (with the DTS 5.1 being the earliest, the commentary being the latest, and the two other Dolby tracks smack bang in the middle with identical sync to 1 ms).

I realise that absolutely nobody will care about this except me, but I'm nonetheless glad I did it, if even just for the amount of stuff I ended up learning in the process. Only now have I finally got some idea of what the hell "Dolby Surround" and "Ultra Stereo" are, for example, partially because I initially tried to append stereo-encoded 192 kbps Dolby versions of the 2018 SC logo from the 2019 German BD and noticed the waveforms (and the audio volumes) were massively different from the 2.0 "surround" tracks I was appending them to. I investigated and discovered that although both tracks did indeed contain two channels of audio information, the "surround" ones used matrix encoding to send specific audio from those two channels to more than 2 speakers in a surround setup during decoding (so instead of just instructing the decoder to spit one whole channel of audio out of each of the front left and right speakers, the signal is spread in a specific, predetermined way between the front two, centre, and back two).

I'll write up a summary of the contents and upload somewhere ASAP, may not be tonight but I can probably manage tomorrow if not. I'm also thinking that since I managed to get everything into the BD-25, there's probably not much point in me having both the BD and MKV versions, since you can just mux the BD image to an MKV if you want one for playing off USB/EHDD on your home setup (and if playing on a computer then you can just mount the ISO and play it as is). I don't really want it to be taking up 50 GB on my storage when it could be taking up 25 GB.

[pipefan413]

Released!