Audio Sync

[murrian]

Hey, I run a bad movie group and for our forth birthday I've managed to snag a cinema to screen our annual birthday celebration film (rubber - it was the first thing we screened and so has become a birthday tradition).

Downside is I couldn't find a DCP copy from any outlet, even though the company offering the PPL couldn't help and the cinema needs DCP.

So, I found DCP-o-matic and got to converting a rip of the blu-ray, I've been using this rip for a couple of years as I find digital files easier to screen in our usual home (a room above a bar) rather than the actual disc itself.

Was quite excited after the computer churned through the transcoding in about three hours but then trying to playback the file in DCP-o-matic's bundled player, vlc, mpc, EasyDCP player & Stereoscopic Player all have a noticeable lag in the video behind the audio (I'm talking several seconds).

This occurs if the file is played from the start or if I jump to a section of the video. Needless to say the original file does not have an audio sync issue. It's originally 5.1 sound and I've left this as default 6 channel in DCP so nothing is being done to the audio above the normal transcoding process.

I've attached the log and metadata files as reading some other posts about audio problems people have asked (however sadly found no solution in those searches).

The cover sheet output states:

Type: Feature
Format: DCI Flat
Audio: 5.1
Audio Language:
Subtitle Language: None
Length: 1h18m59s
Size: 91.1GB

Not sure what extra information I can give? I need to take this to the cinema for Thursday (now is end of Tuesday for me) so really only have tomorrow to try and fix this (I know, short notice, was all a bit of a last minute thing as I nearly got stuck in another state here in Australia due to a covid outbreak).

I've read the manuals, faq (where I got the above player recommendations from) and tried a fair few things myself being vaguely technical (IT engineer for the past two decades) but kinda stumped as to what could be causing this?

I first encoded at 24fps as the application prompted me this would be better compatibility with the cinema projectors and I figure the source being 25fps it should be ok to re-code down, so I initially thought that was the fault but I ran it again at the native 25fps and still have the same problem.

[carl]

Hi, is there an ffprobe.log file inside your project? If so, could you attach it?

There's some logging that I would expect to be there but can't see (perhaps it got lost somehow). Could you just make a new DCP-o-matic project somewhere (anywhere), add your Rubber.mkv file and then send the log from inside the new project? That might show some details about what DCP-o-matic is seeing when it first examines the file.

[carl]

Oh and just in case you have a great internet connection, probably the quickest debugging route would be to send me the Rubber.mkv file (somehow) but I realise that's usually impossible!

[Carsten]

What type of machine did you try playing this? If it's not a very fast CPU, it is quite normal to experience some sync issues with most of the mentioned players. You need to make sure you play the lowest resolution layer.

Three hours for a 1h18m piece however hints towards some beefy CPU. Hmm, the log says ist's 6core Ryzen 5. Not too beefy, but should be able to play the DCP.


@carl: The log shows zillions of

16/02/2021 20:12:28: Writer full; pushes 55026 to disk while awaiting 54939

I see, there was a remote encoding server.

Hmm, that should be irrelevant for the sync issue.




- Carsten

[murrian]

Thanks guys, let me go through these one by one:
@carl:
ffprobe.log weirdly isn't in the second run but the first run (only difference is setting 24fps instead of 25fps) did have one:

Code: Select all

ffprobe version N-92677-ga820b44 Copyright (c) 2007-2018 the FFmpeg developers

  built with gcc 5.4.0 (GCC)

  configuration: --disable-indev=jack --enable-gpl --enable-libx264 --enable-static --enable-shared --prefix=/var/tmp/tmpu2u9xohh --cross-prefix=x86_64-w64-mingw32.shared- --enable-cross-compile --target-os=mingw32 --arch=x86_64 --sysinclude=/opt/mxe/usr/x86_64-w64-mingw32.shared/64/x86_64-w64-mingw32.shared-w64-mingw32 --extra-cflags='-I/var/tmp/tmpu2u9xohh/include -I/opt/mxe/usr/x86_64-w64-mingw32.shared/include' --extra-ldflags='-L/var/tmp/tmpu2u9xohh/lib -L/opt/mxe/usr/x86_64-w64-mingw32.shared/lib'

  libavutil      56. 24.101 / 56. 24.101

  libavcodec     58. 42.100 / 58. 42.100

  libavformat    58. 24.100 / 58. 24.100

  libavdevice    58.  6.101 / 58.  6.101

  libavfilter     7. 46.101 /  7. 46.101

  libswscale      5.  4.100 /  5.  4.100

  libswresample   3.  4.100 /  3.  4.100

  libpostproc    55.  4.100 / 55.  4.100

Input #0, matroska,webm, from 'D:\Rubber.mkv':

  Metadata:

    encoder         : libebml v1.2.0 + libmatroska v1.1.0

    creation_time   : 2011-03-13T00:27:52.000000Z

  Duration: 01:18:59.04, start: 0.000000, bitrate: 9902 kb/s

    Stream #0:0(eng): Video: h264 (High), yuv420p(progressive), 1920x1080, SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 1k tbn, 50 tbc (default)

    Stream #0:1(eng): Audio: dts (DTS), 48000 Hz, 5.1(side), fltp, 1536 kb/s (default)

This ffprobe.log file is identical to the one generated in the new test project I made.
The log file for that test project is:

Code: Select all

17/02/2021 09:44:03: Sub-job Computing digest starting
17/02/2021 09:44:03: Temporal reference was B2B2B2B2B2B2B2B2B2B2B2B2B2B2B2B2
17/02/2021 09:44:03: Video length obtained from header as 118476 frames
17/02/2021 09:44:03: Creating new resampler from 48000 to 50000 with 6 channels
17/02/2021 09:44:03: New graph for 1920x1080, pixel format 0
17/02/2021 09:44:03: FFmpeg: Warning: data is not aligned! This can lead to a speed loss
17/02/2021 09:44:03: New graph for 1920x1080, pixel format 0
17/02/2021 09:44:03: New graph for 1920x1080, pixel format 0
17/02/2021 09:44:03: New graph for 1920x1080, pixel format 0

I notice the resampler there, will try another run with that matched (hadn't noticed the difference on my first two)

I'm uploading the video file to my google drive, it's about 5gb so going to take another forty minutes, can PM the link on request (little cautious about posting a link to copyrighted work).
@Carsten:
My rig is a Ryzen 5 3600 as you noted, it's water cooled so can boost to 4GHz on all cores for the full run (over its 3.6GHz base), 64GB of RAM and reading/writing to high speed SSDs (the source file is on my D drive, a 2.5" Sata SSD with about a 500MB/s read speed and the destination is my C drive, a NVME SSD with about 2000MB/s write speed). I also have a 2070 GPU (MPC utilises GPU for playback which is noticeably smoother than VLC so dropping a lot less frames, but, neither VLC or MPC understand DCP's I think as they pickup the video source but don't pick-up the audio file).

Weird it's showing a remote server as the server was running on the local machine, maybe I set that up wrong and will take a look (though, as you say, one would hope that doesn't cause a problem).

Not sure if it helps but made the classic faux pas of not mentioning I'm running v2.14.47 if that has a bearing.

[carl]

Thanks murrian, I sent you a PM about the link.

Not sure if it helps but made the classic faux pas of not mentioning I'm running v2.14.47 if that has a bearing.

Thanks, that's in the log file so: no problem!

I'll try making a DCP here from your MKV and hopefully the problem will be the same, then I can debug it; though it won't be until around 08:00 GMT that I can look.

[Carsten]

[*]

Weird it's showing a remote server as the server was running on the local machine, maybe I set that up wrong and will take a look (though, as you say, one would hope that doesn't cause a problem).

You may have had the encoding server running without knowing. Once it is running, it hides in the system tray. If it's present, DCP-o-matic will recognise and use it automatically just as if it was running on an external machine. Usually, that doesn't cause problems. Make sure it is not in autostart.

We had a weird audio sync bug once that needed some tweaking, and after it was solved, it turned up later again. I think it had to do with weird audio timestamps. And it was source dependent. There can be so many variations in these AV codecs/containers, you wouldn't believe it...

Maybe we have it again here, it only appeared under exotic circumstances initially - but Carl may already be after it.


Now - given the nature of these players and certain aspects of video/audio sync, it MAY still be that your DCP is perfectly okay. Ultimately, you will only know when playing it at the cinema. You may give this demo player a try: https://we.tl/t-u766iYxIsC

The interface is a bit clunky and it needs a bit of configuring before you can use it, but, give it a try.

[murrian]

Hey guys, thanks for scratching your heads on this one, but, to add a weird twist to the tale, third time's the charm...

I ran the test project I setup this morning and it's in sync, I ran it again at 24fps and that's in sync too. I've included the logs below incase I did make a change without realising it (undercutting the whole "oh yeah, I've got 2 decades as an IT engineer" above)..the log file is too large to attach so linked here.

Have made no other changes from the first runs, really not sure what's going on here but I have my (hopefully) functional DCP to drop off tomorrow!

Now I just need to get my USB stick working, the only one I have large enough given the two 84GB video files (not sure why it makes two) and the 4GB audio has decided today is the day it's going to start crapping out = \

[carl]

Remember you only need the DCP, not DCP-o-matic's working files:

https://dcpomatic.com/manual/html/ch14.html

The reason for the two video files:

https://dcpomatic.com/faq?id=11

Also make sure you format your stick with NTFS

[carl]

It looks like in your failed version you changed the video frame rate at the bottom of the "Timing" tab. I should have spotted that from your first message, sorry!

This control is hidden away in the current development release as it is quite dangerous - it should only be used in the rare event that DCP-o-matic picks up the frame rate of your content incorrectly. That would explain your sync problems...