Variable Frame Rate Recording Detected!


I record shows with H.264/Linear PCM and I’m having sync issues. I noticed it also with HEVC recording. Both the Mediainfo-app and Premiere Pro say that the recording is variable frame rate. I understand that mimoLive is supposed to record in constant frame rate.

mimoLive 5.10
OSX Catalina
MacBook Pro 2019 / 2,3 Ghz 8-Core Intel Core i9 / 16GB / AMD Radeon Pro 5500M 4 GB /
Intel UHD Graphics 630 1536 MB

Audio and video are imported into mimoLive via a single Cam Link 4K usb-3.0 capture card.
There is also an audio drift.


Could you please provide a demo tvShow-Document which causes this phenomenon?


I just tried to generate a small testfile with variable frame rate, but of course could not reproduce it now. It does not happen all the time. I have a large recording from a show which is 12 GB with variable frame rate, but I don’t feel comfortable in sharing it here. If you give me your e-mail address I can send you a download-link. I will paste mediainfo’s properties of the file below.

20210329.tvshow 2021-03-29 12-02-52.mp4
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt 0000.00 (qt )
File size : 11.9 GiB
Duration : 1 h 23 min
Overall bit rate mode : Variable
Overall bit rate : 20.3 Mb/s
Encoded date : UTC 2021-03-29 10:02:52
Tagged date : UTC 2021-03-29 11:26:33
Writing library : Apple QuickTime

ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 2 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 2 frames
Format settings, GOP : M=2, N=30
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 1 h 23 min
Source duration : 1 h 23 min
Bit rate mode : Variable
Bit rate : 17.2 Mb/s
Maximum bit rate : 768 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 25.000 FPS
Minimum frame rate : 12.500 FPS
Maximum frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.333
Stream size : 10.1 GiB (85%)
Source stream size : 10.1 GiB (85%)
Title : Core Media Video
Encoded date : UTC 2021-03-29 10:02:52
Tagged date : UTC 2021-03-29 11:26:33
Codec configuration box : avcC

ID : 2
Format : PCM
Format settings : Signed
Codec ID : lpcm
Duration : 1 h 23 min
Source duration : 1 h 23 min
Bit rate mode : Constant
Bit rate : 3 072 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Bit depth : 32 bits
Stream size : 1.80 GiB (15%)
Source stream size : 1.80 GiB (15%)
Title : Core Media Audio
Encoded date : UTC 2021-03-29 10:02:52
Tagged date : UTC 2021-03-29 11:26:33

Regarding the audio drift: I just did some tests and when I record an hour long testvideo using the CamLink usb 3.0 capture card there is an audio drift of about 80 ms.
When I record the video using Loopback there seems to be no audio drift. So the assumption that the audio-drift problem on T2 Mac’s only occurs when using usb 2.0 doesn’t seem right.

Thank you for the meta data of your recording. I don’t think that the recording is necessary at the moment. I was asking for the mimoLive tvShow-Document.

In case of USB: Are you refering to this?

So, the current document leads to a video with fixed frame-rate? Could it be that it’s a by chance situation, which appears while heavy rendering situations?

Besides, there is no average Frame rate inside of your meta-data.

I’m not sure about this, but maybe a lack of resources could lead to a phenomenon like this: Better to have variable frame-rate, than a broken recording. Is your original recording all the time variable, or does it start, e.g. somewhen after the middle of the recording, to be variable?


Hi JoPhi,

I’m sorry for the misunderstanding. I have a tvShow-document that produced a variable frame-rate recording. You can download it here: Connecting...

Vairable frame-rate recordings have to be converted to constant frame-rate in order for us to edit it in Premiere Pro.

I was indeed referring to de T2-chip audio drift problems. It is stil a problem for us. Loopback keeps it pretty contant, but the offset at the start is different every time.

Thank you for the file. I tested all recording modes. I cannot record any video in Constant Bitrate (CBR). Independently of using your document or other documents, even independently from the codec.

Do you still have Audio-/Video-Sync issues in Premiere Pro, when using 5.10.1 Beta 4?

I don’t have any idea about the techniques behind of mimoLive, but how should it react on frame-drops while CBR? When I compare it to most of the pro cameras, on frame dops, most of simply break/stop the recording.

So you could not record any footage with CFR. That’s remarkable because according to Oliver in this post Mimolive Variable Framerate recording. WHY??? syncing video to audio in Premiere is HELL!!! mimiLive should record in CFR. Is this not the case anymore? I can understand VFR when frames have to be dropped, but I like a CFR recording when there are enough system resources.

That is the point: maybe my systems are not fast enough for it. I can just talk about my tests. The tests I did for you. I do not work with premiere pro, so it’s not important for me.

Hi @j.wierenga

Basically, we hand off video encoding to macOS. We tell it to use CBR but sometimes it seems to decide to use VBR. I’ll have engineering take another look.

If you’re recording for later editing, I recommend to use ProRes. It makes vastly bigger files but editing should be easier and better quality.

Thank you for doing all those tests and for reporting your findings. We’ve tackled the audio drift problem in mimoLive 5.10.1

Can you please check if this fixes that issue for you?

Ah, sorry @j.wierenga, rereading your comments I realize you were talking about Variable Frame Rate. That should not happen. But JoPhi is correct, it could be that macOS decides to drop frames and adapt the frame rate if the storage medium isn’t fast enough or if mimoLive isn’t sending enough frames. Do you have a message in the File Recording output to that effect?

This was my fault, I brought VBR into the play. :hugs: