Split video and audio tracks in seperate files from a MKV source file

[ElegantRain]

Hi everyone, I'm recording video and audio for my podcast and I'm in the process of automating all the steps I can to make it easier for the editor in post production.

We're 4 animators in different studios. We're streaming the live recording on my Twitch channel to profit visibility so we're using OBS to create virtual cameras used in OBS Ninja for the live stream. We're recording locally x264 video stream with pcm_s24le lossless audio in a MKV container. Both editors are using Premiere Pro and Audition. Since MKV isn't supported in Premiere I created this batch file to split the audio stream and remux the video stream in a mp4 container.

@echo off & setlocal enabledelayedexpansion
for %%v in ("*.mkv") do (
  set FileName=%%v
  set name=!FileName:~0,-4!

  set outname=C:\Users\Freeman\Videos\!name!
  echo Remuxing: !name! to !outname!

  ffmpeg -i "!FileName!" -map 0:v -c copy "!outname!.mp4" -map 0:a:0 -c copy "!outname!_0.wav"
)
pause

It's almost working but I'm getting the following error

[mp4 @ 0000024ee3b2f040] Non-monotonous DTS in output stream 0:0; previous: 0, current: 0; changing to 1. This may result in incorrect timestamps in the output file.

[Attachment 60505 - Click to enlarge]

As you can see on the screenshot above the audio stream is longer than the video. How can I fix this?

Thanks!

* I'm using the latest ffmpeg build as of today.

[poisondeathray]

I suspect the cause is variable frame rate (VFR)

Even if you recorded CFR in OBS, the container timebase between MKV and MP4 is different and that can lead to jitter in the timestamps.

Newer PP versions handle VFR better, but it's still not great

(Some point releases of PP could actually import MKV)


1) check that you recorded CFR in the original. An easy check method is mediainfo view=>text, or you can use ffmpeg vfrdet

If not, you need to re-encode and convert to CFR . If you start with VFR, and it's more than minimally VFR (min/max deviations are more than tiny), it's not really "fixable" because you're missing frames. Converting to CFR inserts duplicate frames at approximately the correct places to keep everything in sync and duration matched up

2) check what framerate PP "thinks" the imported MP4 framerate is - e.g. if it was supposed to be 30.0 FPS, and it's 29.564 or some weird number, the issue is likely VFR interpretation in the remuxed MP4

2b) if that's the case use mp4fpsmod to fix the timestamps to make it CFR, reimport (that is, if your case was the minimally variable case, such as timestamp jitter. If it was the massive deviations and frame drop VFR, then you need to re-encode)

[ElegantRain]

Even if you recorded CFR in OBS, the container timebase between MKV and MP4 is different and that can lead to jitter in the timestamps.

Is there another container that wouldn't cause timebase misinterpretation?

1) check that you recorded CFR in the original. An easy check method is mediainfo view=>text, or you can use ffmpeg vfrdet

As you can see the remuxed file is VBR instead of CBR, why does ffmpeg doesn't keep it as a CBR file? Can I add something in my command to force CBR? Also it's really strange that to get 60 FPS I need to set 59.94 FPS in the OBS options. If I set 60 FPS in OBS options I get 60.119 FPS. I still have the error in ffmepg and it's still not synced in Premiere.

Here's the MediaInfo for a 15 seconds test

General
Unique ID : 199157449624611465003073718188215867930 (0x95D4545FE0C8DCF98A3B20DA8FE39A1A)
Complete name : C:\Users\Freeman\Videos\2021-08-31 15-22-02.mkv
Format : Matroska
Format version : Version 4
File size : 23.5 MiB
Duration : 15 s 449 ms
Overall bit rate : 12.7 Mb/s
Writing application : Lavf58.29.100
Writing library : Lavf58.29.100
ErrorDetectionType : Per level 1

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 15 s 449 ms
Bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 60.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.080
Stream size : 18.8 MiB (80%)
Writing library : x264 core 161 r3020 d198931
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=24 / lookahead_threads=8 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=10 / rc=abr / mbtree=1 / bitrate=10000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 2
Format : PCM
Format settings : Little / Signed
Codec ID : A_PCM/INT/LIT
Duration : 15 s 82 ms
Bit rate mode : Constant
Bit rate : 2 304 kb/s
Channel(s) : 2 channels
Sampling rate : 48.0 kHz
Bit depth : 24 bits
Stream size : 4.14 MiB (18%)
Default : Yes
Forced : No

MediaInfo of the same file remuxed by ffmpeg

General
Complete name : C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 19.3 MiB
Duration : 15 s 465 ms
Overall bit rate : 10.5 Mb/s
Writing application : Lavf59.4.102

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 15 s 465 ms
Source duration : 15 s 430 ms
Bit rate : 10 000 kb/s
Maximum bit rate : 10.5 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 59.940 (59940/1000) FPS
Minimum frame rate : 31.250 FPS
Maximum frame rate : 16 000.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.080
Stream size : 19.3 MiB (100%)
Source stream size : 19.3 MiB (100%)
Writing library : x264 core 161 r3020 d198931
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=24 / lookahead_threads=8 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=10 / rc=abr / mbtree=1 / bitrate=10000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
mdhd_Duration : 15465
Codec configuration box : avcC

2b) if that's the case use mp4fpsmod to fix the timestamps to make it CFR, reimport (that is, if your case was the minimally variable case, such as timestamp jitter. If it was the massive deviations and frame drop VFR, then you need to re-encode)

Reading this link it seems complicated to me. Any help would be greatly appreciated to add a line of code to my actual code. I can add PATH for qaac64.exe and refalac64.exe but I don't understand the command to add in my .bat file.

Is there a way to add MKV codec in Premiere Pro? I remember I've successfully added Prores codecs in my install of PP.

Thanks for helping!

[poisondeathray]

As you can see the remuxed file is VBR instead of CBR, why does ffmpeg doesn't keep it as a CBR file? Can I add something in my command to force CBR?

VFR = variable frame rate
VBR = variable bit rate

We're talking about VFR here

First try adding
-video_track_timescale 60

The timebase ffmpeg uses for mp4 when you remux a 60/1 fps input is 16k for some reason . This should make it 60K . On a small 60/1 FPS test, it corrected the issue for me

Even if you recorded CFR in OBS, the container timebase between MKV and MP4 is different and that can lead to jitter in the timestamps.

Is there another container that wouldn't cause timebase misinterpretation?

I don't know what the options are in obs, bit a transport stream (.ts, .m2ts, .mts) or MOV would be ideal because you can store the uncompressed audio as well. You wouldn't have to remux anything, or import 2 streams. Open source MP4 muxers do not support uncompressed audio

Is there a way to add MKV codec in Premiere Pro? I remember I've successfully added Prores codecs in my install of PP.

No, but Adobe added it for a few versions, then took it away

(There are workaround, where you can frameserve in, but more hassle than you probably want to do, because it's decoded in another application, and there's lots of overhead)


If the -video_track_timescale 60 does not solve the issue for you (and check in PP) , I'll walk you through mp4fpsmod

[ElegantRain]

First try adding
-video_track_timescale 60

The timebase ffmpeg uses for mp4 when you remux a 60/1 fps input is 16k for some reason . This should make it 60K . On a small 60/1 FPS test, it corrected the issue for me

Not sure I added the parameter correctly, is that correct? Looks like it's correcting something but it's not working.

ffmpeg -i "!FileName!" -video_track_timescale 60 -map 0:v -c copy "!outname!.mp4" -map 0:a:0 -c copy "!outname!_0.wav"

Still having the same issue, here's the remuxing log https://pastebin.com/UD6u4gyw

I don't know what the options are in obs, bit a transport stream (.ts, .m2ts, .mts) or MOV would be ideal because you can store the uncompressed audio as well. You wouldn't have to remux anything, or import 2 streams. Open source MP4 muxers do not support uncompressed audio

The .ts, .m2ts, .mts and .mov formats gets corrupted if OBS crash. MKV have the advantage to protect the file from breaking upon crash.

And yes I really don't like the MP4 container especially for podcasting where you need uncompressed audio for post-prod.

https://www.autokroma.com/Influx/Download

I've found out this software in beta, I'll try it to see.

[poisondeathray]

Maybe slightly different input test files, but my input MKV was 60/1 fps CFR, and the streamcopy output MP4 was VFR too, but less deviation between min/max

Frame rate mode : Variable
Frame rate : 60.000 FPS
Minimum frame rate : 57.762 FPS
Maximum frame rate : 62.500 FPS

So that suggests timestamp jitter on my file, and that's correctable by replacing the timestamps using mp4fpsmod

But you have some massive deviation with the max fps, usually that indicates some other problems, so I'm not sure if it will work for you but you should try mp4fpsmod anyways
Minimum frame rate : 31.250 FPS
Maximum frame rate : 16 000.000 FPS


For mp4fpsmod, the author used to have binaries compiled on old homepage, but I think they took google sites down

I attached a mirror

You'd use it like this

"mp4fpsmod" --fps 0:60 -o "output.mp4" "input.mp4"

It supports inplace editing (overwrite input file, instead of a 2nd file), but I wouldn't recommend it when you're just testing things out

[poisondeathray]

If it still does not work, another option is to skip ffmpeg. Use mkvextract, mp4box or lsmash in a batch

[ElegantRain]

"mp4fpsmod" --fps 0:60 -o "output.mp4" "input.mp4"

It supports inplace editing (overwrite input file, instead of a 2nd file), but I wouldn't recommend it when you're just testing things out

I'm not tech enough to add it to my batch file. I've tried many combinations but it's not working. Can you guide me? I've tried that

@echo off & setlocal enabledelayedexpansion
for %%v in ("*.mkv") do (
  set FileName=%%v
  set name=!FileName:~0,-4!

  set outname=C:\Users\Freeman\Videos\!name!
  echo Remuxing: !name! to !outname!

  mp4fpsmod --fps 0:60 -o "!outname!.mp4" "!name!.mp4"

)
pause

The google site seems still up https://sites.google.com/site/qaacpage/

[poisondeathray]

qaac is an audio encoder

qaac - CLI QuickTime AAC/ALAC encoder
https://github.com/nu774/qaac

The original cabinet page is down - and you want mp4fpsmod.exe, not qaac64.exe

eg. you can check the wayback machine , it looks very different and has compiled binaries

https://web.archive.org/web/20191008021708/https://sites.google.com/site/qaacpage/cabinet

[ElegantRain]

qaac is an audio encoder

qaac - CLI QuickTime AAC/ALAC encoder
https://github.com/nu774/qaac

The original cabinet page is down - and you want mp4fpsmod.exe, not qaac64.exe

eg. you can check the wayback machine , it looks very different and has compiled binaries

https://web.archive.org/web/20191008021708/https://sites.google.com/site/qaacpage/cabinet

Sorry I've noticed after replying and I edited my message but too late. I've succesfully installed it and added the path to windows.

I've tried the code like that

@echo off & setlocal enabledelayedexpansion
for %%v in ("*.mkv") do (
set FileName=%%v
set name=!FileName:~0,-4!

set outname=C:\Users\Freeman\Videos\!name!
echo Remuxing: !name! to !outname!

mp4fpsmod --fps 0:60 -o "!outname!.mp4" "!name!.mp4"

)
pause

I'm getting this output error

Remuxing: 2021-08-31 15-22-02 to C:\Users\Freeman\Videos\2021-08-31 15-22-02
Reading MP4 stream...
Done reading
Saving MP4 stream...
libmp4v2: mp4v2::impl::MP4File::Open: open(C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4) failed (..\..\mp4v2\src\mp4file.cpp,371)
Press any key to continue . . .

Thanks for your help, I really appreciate it. The other podcast animators appreciate it too!

[poisondeathray]

I do not see ffmpeg in that command . mp4fpsmod cannot read a mkv . How are you taking the mkv and remuxing to mp4 in that current version ?

Before you waste time writing a batch. Try 1 file first with that workflow. I don't have high hopes when the mix/max fps deviation rates when processed with ffmpeg are so large

[ElegantRain]

I do not see ffmpeg in that command . mp4fpsmod cannot read a mkv . How are you taking the mkv and remuxing to mp4 in that current version ?

Before you waste time writing a batch. Try 1 file first with that workflow. I don't have high hopes when the mix/max fps deviation rates when processed with ffmpeg are so large

Well I've made 2 batch files, one for remuxing the MKV to MP4

@echo off & setlocal enabledelayedexpansion
for %%v in ("*.mkv") do (
  set FileName=%%v
  set name=!FileName:~0,-4!

  set outname=C:\Users\Freeman\Videos\!name!
  echo Remuxing: !name! to !outname!

  ffmpeg -i "!FileName!" -map 0:v -c copy "!outname!.mp4" -map 0:a:0 -c copy "!outname!.wav"

)
pause

and one for fixing the mp4 timebase

@echo off & setlocal enabledelayedexpansion
for %%v in ("*.mkv") do (
  set FileName=%%v
  set name=!FileName:~0,-4!

  set outname=C:\Users\Freeman\Videos\!name!
  echo Remuxing: !name! to !outname!

  mp4fpsmod --fps 0:60 -o "!outname!.mp4" "!name!.mp4"

)
pause

Thanks for your help!

[poisondeathray]

Should the 2nd one be *.mp4 ? for %%v in ("*.mkv") looks for mkv, not mp4. mp4fpsmod only works on mp4

[ElegantRain]

Should the 2nd one be *.mp4 ? for %%v in ("*.mkv") looks for mkv, not mp4. mp4fpsmod only works on mp4

Damn I feel stupid. I changed it and still getting an error

Remuxing: 2021-08-31 15-22-02 to C:\Users\Freeman\Videos\2021-08-31 15-22-02
Reading MP4 stream...
Done reading
Saving MP4 stream...
libmp4v2: mp4v2::impl::MP4File::Open: open(C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4) failed (..\..\mp4v2\src\mp4file.cpp,371)
Press any key to continue . . .

[poisondeathray]

Remuxing: 2021-08-31 15-22-02 to C:\Users\Freeman\Videos\2021-08-31 15-22-02
Reading MP4 stream...
Done reading
Saving MP4 stream...
libmp4v2: mp4v2::impl::MP4File::Open: open(C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4) failed (..\..\mp4v2\src\mp4file.cpp,371)
Press any key to continue . . .

Not sure

Check if "C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4" is a valid file

Try it from the commandline on a single file first

"mp4fpsmod" --fps 0:60 -o ""C:\Users\Freeman\Videos\output.mp4" "C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4"

This simple batch works for me

for %%a in ("*.mp4") do "mp4fpsmod" --fps 0:60 -o "mp4fpsmod_%%~na.mp4" "%%a"

pause

[ElegantRain]

Remuxing: 2021-08-31 15-22-02 to C:\Users\Freeman\Videos\2021-08-31 15-22-02
Reading MP4 stream...
Done reading
Saving MP4 stream...
libmp4v2: mp4v2::impl::MP4File::Open: open(C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4) failed (..\..\mp4v2\src\mp4file.cpp,371)
Press any key to continue . . .

Not sure

Check if "C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4" is a valid file

Try it from the commandline on a single file first

"mp4fpsmod" --fps 0:60 -o ""C:\Users\Freeman\Videos\output.mp4" "C:\Users\Freeman\Videos\2021-08-31 15-22-02.mp4"

This simple batch works for me

for %%a in ("*.mp4") do "mp4fpsmod" --fps 0:60 -o "mp4fpsmod_%%~na.mp4" "%%a"

pause

Finally got mp4fpsmod to work but unfortunately it's not fixing it correctly as you though it would. At least now MediaInfo sees it as a 60 FPS timecode instead of the 59.94 FPS from the .mp4 remux file.

The remux.mp4 file is the one created by ffmpeg from the .mkv and the output.mp4 file is the files outputted by mp4fpsmod.


[Attachment 60614 - Click to enlarge]

Thank you for helping!

[ElegantRain]

When posting my last comment I though that the results didn't made any sense. How could a MKV file at 60 fps remuxed in MP4 could become a 59.94 FPS file. So I went and recorded 4 short clips with OBS Studio and found out the MKV encoder acting strangely. I'll paste the MediaInfo interesting informations and what was the original recording format.

MKV(x264/pcm_s24le) - 59.94 FPS
https://www110.zippyshare.com/v/QvLQStGn/file.html

Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1 min 0 s
Bit rate : 9 374 kb/s
Nominal bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 60.000 FPS

Full MediaInfo https://pastebin.com/Ctkv1vAw

MKV(x264/pcm_s24le) - 60 FPS
https://www84.zippyshare.com/v/N44PIPZS/file.html

Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1 min 0 s
Bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 60.119 FPS

Full MediaInfo https://pastebin.com/zSRRccYZ

MP4(x264/aac) - 59.94 FPS
https://www84.zippyshare.com/v/wMcyNFeY/file.html

Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1 min 0 s
Bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 59.940 (60000/1001) FPS

Full MediaInfo https://pastebin.com/BkshFD6N

MP4(x264/aac) - 60 FPS
https://www84.zippyshare.com/v/Fh3sKuzq/file.html

Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1 min 0 s
Bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 60.000 FPS

Full MediaInfo https://pastebin.com/GcwJSZPU

As you can see the framerate isn't respected recording in MKV format where 59.94 FPS ends up as 60 FPS and 60 FPS ends up as 60.119 FPS.

That's maybe a reason that when I remux those MKV files with ffmpeg they get back at 59.94 FPS or 60 FPS.

What the h*** is going on!?

-> Post on OBS forum asking what is going on

[poisondeathray]

I think your 1st link is wrong ; it's the same link as the 3rd video

Are the MP4 versions remuxed with ffmpeg, default settings ?

[ElegantRain]

I think your 1st link is wrong ; it's the same link as the 3rd video

Are the MP4 versions remuxed with ffmpeg, default settings ?

Sorry I've just edited the first link.

The 4 files are untouched recordings from OBS. Nothing have been remuxed in ffmpeg.

[poisondeathray]

Looking at mkv-60.mkv, if your clip is 1min , why is the audio longer ? You can verify in PP, and audio editors

If you extract the elementary streams (e.g. mkvextract) this will discard the buggy timecodes completely. You can then remux with MP4box with the proper framerate.

But you don't even have to do that , PP can import elementary AVC stream directly

When you do that, you can see the audio is longer than the video, but it looks in sync. But you need a longer test sample to check for drift and sync. If it's in sync for a 3-4 hours sample, that's all you really need, right ? Unless you're doing longer recordings, then check that duration

3604 is the last frame in PP, which checks with elementary stream parsers - so it's correct.

[ElegantRain]

Looking at mkv-60.mkv, if your clip is 1min , why is the audio longer ? You can verify in PP, and audio editors

If you extract the elementary streams (e.g. mkvextract) this will discard the buggy timecodes completely. You can then remux with MP4box with the proper framerate.

But you don't even have to do that , PP can import elementary AVC stream directly

When you do that, you can see the audio is longer than the video, but it looks in sync. But you need a longer test sample to check for drift and sync. If it's in sync for a 3-4 hours sample, that's all you really need, right ? Unless you're doing longer recordings, then check that duration

3604 is the last frame in PP, which checks with elementary stream parsers - so it's correct.

This makes sense. I'm currently trying to record a 3 hours test and will import it in PP and let you know if there's a desync.

In the meantime could you explain me the whole 60.119 FPS thing? Why is this?

Thank you!

[poisondeathray]

In the meantime could you explain me the whole 60.119 FPS thing? Why is this?

Normally it's jitter in the timestamps, because of the MKV timebase 1/1000. ie. It's not precise enough . 1ms

If you extract the timestamps, the delta PTS varies between frame. You cannot divide 1/60 (~ 0.0166666...) evenly into that timebase resulting in an exact value each frame. So each entry rounds up or down.

A "normal" 60/1 FPS CFR in MP4 looks like this: the delta PTS is constant, and predictable

# timecode format v2
0.00
16.67
33.33
50.00
66.67
83.33
100.00
116.67
133.33
150.00
166.67
183.33
200.00
216.67
.
.

MKV container specs only allow 1ms, so values are rounded to the nearest ms . So you get a delta PTS of 16 or 17, and that is variable.

0
17
33
50
67
83
100
117
133

I'm not sure how mediainfo calculates how it declares "constant", but in actual recordings, sometimes at the beginning or end, there are duplicate frames as recording "warms up" so that can cause deviation. Also, frame drops can cause deviation from the constant pattern . Any deviation is technically variable frame rate



But of we take mkv-60.mkv, track 1 timestamps are really buggy, it looks like this

# timestamp format v2
0
21
43
64
85
107
128
149
171
192
213
235
256
.
.

delta is 21,22.. etc. and at the end there are repeats. But ~ 21 delta PTS average means the fps is ~47 , not 60

1/60 =~ 0.016666.. . So you should be seeing 16.7 ms for each entry (again round up, round down) , but the point 21 suggests a different framerate

There might be something else going on with the audio timestamps, but this is abnormal

[ElegantRain]

In the meantime could you explain me the whole 60.119 FPS thing? Why is this?

Normally it's jitter in the timestamps, because of the MKV timebase 1/1000. ie. It's not precise enough . 1ms

If you extract the timestamps, the delta PTS varies between frame. You cannot divide 1/60 (~ 0.0166666...) evenly into that timebase resulting in an exact value each frame. So each entry rounds up or down.

A "normal" 60/1 FPS CFR in MP4 looks like this: the delta PTS is constant, and predictable

# timecode format v2
0.00
16.67
33.33
50.00
66.67
83.33
100.00
116.67
133.33
150.00
166.67
183.33
200.00
216.67
.
.

MKV container specs only allow 1ms, so values are rounded to the nearest ms . So you get a delta PTS of 16 or 17, and that is variable.

0
17
33
50
67
83
100
117
133

I'm not sure how mediainfo calculates how it declares "constant", but in actual recordings, sometimes at the beginning or end, there are duplicate frames as recording "warms up" so that can cause deviation. Also, frame drops can cause deviation from the constant pattern . Any deviation is technically variable frame rate



But of we take mkv-60.mkv, track 1 timestamps are really buggy, it looks like this

# timestamp format v2
0
21
43
64
85
107
128
149
171
192
213
235
256
.
.

delta is 21,22.. etc. and at the end there are repeats. But ~ 21 delta PTS average means the fps is ~47 , not 60

1/60 =~ 0.016666.. . So you should be seeing 16.7 ms for each entry (again round up, round down) , but the point 21 suggests a different framerate

There might be something else going on with the audio timestamps, but this is abnormal

Hi and sorry for the late reply, I've been busy with work and the process of buying a house.

To be honest I'm not sure about all of the technical data you've talked about in your latest reply. I'm not sure I have to understand it anyway as I believe that you're right.

I've tried recording a 10 hour file and it was broken. Audio track unreadable and video track only had 6 hours of data.

I've tried a shorter record of 4 hours and it's working. My batch file copy the video in a mp4 container and my audio is copied in a wav container which all import great in Premiere Pro and plays back without A/V desync.

Here's a MediaInfo of the MKV file

General
Unique ID : 283030676027590313016091945283295180801 (0xD4EDB9B4BE37AE417C871C69AB74F801)
Complete name : C:\Users\Freeman\Videos\MediaTrans\2021-09-09 12-20-00.mkv
Format : Matroska
Format version : Version 4
File size : 21.5 GiB
Duration : 4 h 38 min
Overall bit rate : 11.0 Mb/s
Writing application : Lavf58.29.100
Writing library : Lavf58.29.100
ErrorDetectionType : Per level 1

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 4 h 38 min
Bit rate : 9 289 kb/s
Nominal bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 60.119 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.075
Stream size : 18.1 GiB (84%)
Writing library : x264 core 161 r3020 d198931
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=24 / lookahead_threads=8 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=10 / rc=abr / mbtree=1 / bitrate=10000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 2
Format : PCM
Format settings : Little / Signed
Codec ID : A_PCM/INT/LIT
Duration : 4 h 38 min
Bit rate mode : Constant
Bit rate : 1 536 kb/s
Channel(s) : 2 channels
Sampling rate : 48.0 kHz
Bit depth : 16 bits
Stream size : 2.99 GiB (14%)
Default : Yes
Forced : No

Here's the MediaInfo of the remuxed MP4 file

General
Complete name : C:\Users\Freeman\Videos\MediaTrans\2021-09-09 12-20-00.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 18.5 GiB
Duration : 4 h 38 min
Overall bit rate : 9 512 kb/s
Writing application : Lavf59.4.102

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.2
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 4 h 38 min
Source duration : 4 h 38 min
Bit rate : 9 503 kb/s
Nominal bit rate : 10 000 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 60.000 FPS
Minimum frame rate : 31.250 FPS
Maximum frame rate : 16 000.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.076
Stream size : 18.5 GiB (100%)
Source stream size : 18.5 GiB (100%)
Writing library : x264 core 161 r3020 d198931
Encoding settings : cabac=1 / ref=1 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=2 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=0 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=0 / threads=24 / lookahead_threads=8 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=1 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=10 / rc=abr / mbtree=1 / bitrate=10000 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
mdhd_Duration : 16712449
Codec configuration box : avcC

Here's a MediaInfo of the wav file

General
Complete name : C:\Users\Freeman\Videos\MediaTrans\2021-09-09 12-20-00.wav
Format : Wave
File size : 2.99 GiB
Duration : 4 h 38 min
Overall bit rate mode : Constant
Overall bit rate : 1 536 kb/s
Writing application : Lavf59.4.102

Audio
Format : PCM
Format settings : Little / Signed
Codec ID : 1
Duration : 4 h 38 min
Bit rate mode : Constant
Bit rate : 1 536 kb/s
Channel(s) : 2 channels
Sampling rate : 48.0 kHz
Bit depth : 16 bits
Stream size : 2.99 GiB (100%)

I'll try to record a 3 hour video file in 30 FPS instead of 60 FPS as you're saying that in fact it's not 60 FPS anyway.

In the meantime if you have additionnal hints, information or constatation please share it with me!

Thank you a lot!

[ElegantRain]

New information. On this thread on the OBS forum, someone said that information explaining why the MKV file is like that.

Unfortunately, small precision is set in the FFmpeg (OBS uses it to write the files)... and this way it works everywhere:

FFmpeg: libavformat/matroskaenc.c Source File

Code:
// ms precision is the de-facto standard timescale for mkv files
avpriv_set_pts_info(s->streams[i], 64, 1, 1000);

Nothing to fix on OBS side.

I'm not sure what does it mean in all honesty. We're recording our first podcast this Monday and hope the best!

Thank you for all your help!

[poisondeathray]

For the precision issue - it's not ffmpeg/libavformat's fault, they are just following MKV container specs . To code more precision would break specifications

But the timestamps are buggy regardless of the precision issue - There is more than 1 issue at play here

Is lossless audio that important? Or using MKV container (are you expecting interruptions or technical difficulties) ? I'd think sync would be highest priority

[ElegantRain]

But the timestamps are buggy regardless of the precision issue - There is more than 1 issue at play here

Any ideas on how to fix this? I may have done a mistake configuring ffmpeg custom recording in OBS. Could it be the keyframe interval?


[Attachment 60703 - Click to enlarge]

Is lossless audio that important? Or using MKV container (are you expecting interruptions or technical difficulties) ? I'd think sync would be highest priority

Yes lossless audio is important as it's impossible to edit audio efficiently when it's compressed.

[poisondeathray]

Any ideas on how to fix this? I may have done a mistake configuring ffmpeg custom recording in OBS. Could it be the keyframe interval?

Not the keyframe interval. That only affects max distance IDR frame placement for libx264 ; it does not affect timestamps

[ElegantRain]

Any ideas on how to fix this? I may have done a mistake configuring ffmpeg custom recording in OBS. Could it be the keyframe interval?

Not the keyframe interval. That only affects max distance IDR frame placement for libx264 ; it does not affect timestamps

Then is there anything I could try in Muxer Settings or in Video Encoder Settings or OBS is just broken at making MKV files?

Thank you for your help it's really appreciated.

[poisondeathray]

Then is there anything I could try in Muxer Settings or in Video Encoder Settings or OBS is just broken at making MKV files?

There is a --force-cfr switch in x264, but I doubt it will help because the issue definitely is not the encoder

[ElegantRain]

Then is there anything I could try in Muxer Settings or in Video Encoder Settings or OBS is just broken at making MKV files?

There is a --force-cfr switch in x264, but I doubt it will help because the issue definitely is not the encoder

And where should I search for the issue? Report on OBS Github?