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Need help with audio drifting out of sync

Hi Screenflow community,

 

• Computer hardware including screen size: Late 2015 iMac Retina 5k 27-inch. 4 GHz Quad-Core Intel Core i7. 24 GB 1867 Mhz DDR3 Ram, 500GB SSD, AMD Radeon R9 M395X 4GB GPU. Facetime HD Camera.
• OS version 10.15.1 macOS Catalina
• ScreenFlow version: Recorded video with latest version of 8. Upgraded to 9 after recording.
• External devices: Rode Podcaster connected via USB.
• Free hard drive space: 77.4 GB
• Number of Monitors: 1
• Recording settings: Record Desktop from iMac. Record Video from FaceTime HD Camera (Built-In) Format 640x480. Record Audio from RODE Podcaster v2 (Audio Sample Rate 96Khz)
• What you are recording: Google Slides presentation in Google Chrome
• Exported file: https://drive.google.com/file/d/1FbPy0pXK43AdcWj9gb8Dp4QMY0wvHEy1/view?usp=sharing

 

I'm using a late 2015 iMac Facetime HD camera, Rode Podcaster microphone, and the program Screenflow to record a 1 hour video presentation. For the first 20 minutes or so of the video the audio of me talking is in sync with the Facetime HD webcam footage. But slowly the audio begins to drift and falls out of sync with the Facetime HD webcam footage.

 

When I run the video file through ffmpeg with this command: "ffmpeg -y -i shopify_vsl_2.mp4 -af 'aresample=async=1000' -movflags faststart -r 30 -vsync vfr -f mp4 shopify_vsl_2_cfr.mp4" and force a constant frame rate the audio and webcam footage stay in sync much longer--but do still end up drifting.

 

The main thing that command does is force a constant frame rate of 30 frames per second in the footage and it drops duplicate frames.

 

My hunch is that the root of the problem is the Facetime HD camera does not maintain a constant frame rate but has a variable frame rate that changes depending on lighting and other factors. Other hypotheses are that the Rode Podcaster's audio sample rate (96Khz) isn't what Screenflow expects (Screenflow exported mp4s look to have an audio sample rate of 44.1Khz). I tried downsampling the audio to 44.1Khz in Audacity and adding it back in Screenflow and that made the audio syncing issues worse. I tried downsampling the audio to 48Khz in Audacity too but I was unable to do so because when I opened the audio file in audacity it registered as 48Khz already (even though in Audio MIDI Setup the Rode Podcaster input format was set to 96Khz when I recorded).

 

Does anyone have any recommendations on how to eliminate audio drifting out of sync when recording videos with Screenflow?

 

Kind regards,

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view

    Are you using ScreenFlow 9.0.1?

    Just as a test to compare, try using Facetime camera and the iMac's built in microphone. 

    Clocks over time can drift.

    You can check device sample rates in Apple's Audio Midi Setup utility.
    This from my Behringer U-Phoria
     

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  • @craigs I recorded it on Screenflow 8.2.5. I've since updated. I'm going to try recording on the latest version to see if that's it.

     

    Do you have a recommended test I can run to see if clocks drift? For example leave screenflow recording an hour of a metronome web page making tick sounds picked up by the RODE Podcaster? And doing the same test but with the iMac's built in microphone?

     

    Regarding device audio sample rates what sample rate should be selected in Apple's Audio Midi Setup? RODE Podcaster is 96Khz by default but I can change it to 44.1Khz or 48Khz if Screenflow needs that audio sample rate.

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view
    Harry Whelchel said:
    Do you have a recommended test I can run to see if clocks drift?

     Yes, first test with Facetime and internal Mic. If the issue still happens we know it's not specific to external devices (and clocks).

    A metronome is fine but basically anything where sync can be observed over time. Pointing at a TV for example. Since the audio only needs to observed at head and tails of the recording it could even be an occasional hand clap.

    Once you determine whether the issue exists internally we can move on to the Rode. I would test 44.1kHz first and then 48kHz next.

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  • CraigS thanks Craig I'm going to try some tests later today.

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view

    Harry Whelchel You're welcome of course. The results could help us narrow things down.

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  • CraigS ok I've run three tests at different audio sample rates:

    Setup: Rode Podcaster, Screenflow, and Facetime HD Camera

    • 96khz: Audio Drifted
    • 48khz: Audio Drifted
    • 44.1khz: Audio Did Not Drift

    What is the significance of this?

    Would you like me to still do some recording tests with a program like QuickTime instead of Screenflow?

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view

    Harry Whelchel 

    Harry Whelchel said:
    Setup: Rode Podcaster, Screenflow, and Facetime HD Camera

    96khz: Audio Drifted
    48khz: Audio Drifted
    44.1khz: Audio Did Not Drift

     Absolutely report this and well test on our end, It shouldn't drift on 48kHz.
    ScreenFlow Support Form

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  • CraigS cool I have done so. Just tested 88.2khz and it did not drift on that as well.

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view

    Harry Whelchel Do report that. That's a direct relationship to 44.1kHz. So the issue may be specific to 48kHz (and 96kHz is a direct relationship to that).

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  • CraigS Got it thanks I've done so.

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view

    Harry Whelchel You're welcome of course. Those are interesting findings for us.

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  • Harry Whelchel I'd love to know if you fixed this issue, as I too feel I'm having the same problem with a Mac pro and using an external audio interface and Rode Podcaster but with a Logitech C920 webcam where the variable frame rate causes the audio to drift after about 25mins. I always choose to export at 48k because that's the video standard right? maybe that's the problem? I'm using Screenflow 9 by the way, set to 30FPS. Thanks in advance.

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    • Sara Carter I did fix it. Went into "Audo MIDI Setup" and set the format to 88.2hz

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    • Harry Whelchel Thanks Harry, I'll give that a try. Glad you were able to fix it!

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 2 yrs ago
    • Reported - view
    Sara Carter said:
    I'm having the same problem with a Mac pro 

     A 2013 and 2019 Mac Pro are different so the model might be significant. Making sure there's nothing else on the USB bus (multiple ports can be on the same bus) might be a factor. We are investigating sync issues so please do fill out the previously posted form link but you must include very complete details as if you wanted someone to build a matching setup.

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    • CraigS Thanks for your reply. I'm on a late 2013 Mac Pro but I will look at the link. 

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      • CraigSModerator
      • Telestream Desktop Forum Moderator
      • CraigS
      • 2 yrs ago
      • Reported - view

      Sara Carter Thanks for that. We're working on the issue so any details you provide in the form can help.

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    • CraigS I don't know if this is a red herring but after researching this issue I came up with a probable reason being the Logitech webcam using a variable frame rate during recording. People were fixing this issue by running the recording through Handbrake app and rendering the file as constant framerate. I hope this helps.

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      • CraigSModerator
      • Telestream Desktop Forum Moderator
      • CraigS
      • 2 yrs ago
      • Reported - view
      Sara Carter said:
      a probable reason being the Logitech webcam using a variable frame rate during recording.

       That's certainly a possible reason for sure.

      Like
  • Greetings all.  

    Is there a solution for this problem yet?   I've been recording lectures the last 4 months, and in the last weeks I started having this problem (I didn't have it before).  The audio (somewhat randomly) goes out of sync during a 3 hour recording.  Some times the problem starts at the beginning of a recording, other times it is later in the lecture.  I've (sort of) corrected the synchronisation problem by detaching the audio from the web cam frame in ScreenFlow and moving it around, but the amount of offset / desynchronization varies throughout the video.  Extremely frustrating and impossible to 100% fix.

    Software:  ScreenFlow 9.0.5. Recording at 30 fps. OS = Catalina (earlier) and Big Sur (now)

    Hardware:

    •     MacBook Pro 16" v2020, 64GB RAM, Large SSD space available.  
    •     Apogee Hypemic (plugged into Thunderbolt port, some times using an extension cable - haven't tested if the extension cable is the problem) 
    •     Logitech C920 Webcam (plugged into either a USB 2 or 3 port - haven't tested if this makes the difference).  

    I have 4 good studio lights illuminating me so lighting is constant and I wouldn't expect the web cam to change frame rates due to lighting variations.

    The Apple Audio Midi setup app says the mic is working at 98GHz. 

    ** Side note:  I've had the same random audio/video offset problem using the same software / hardware above, but recording me with a Nikon Z7 in video mode with a Sennheiser MKE440 stereo mike, and a Cam Link HDMI video capture device going into the Mac vis USB.  So, I don't think the Logitech cam is the issue.

    Questions needing answers (pretty please):

    1. Is there is fix for this problem?

    2. Does it matter that I'm doing 3 hour recordings (e.g. would 1 hour be better)? For example, I'm wondering if there is a 'buffer' on the Mac/Screenflow that is getting filled after a while and the Mac is subsampling the video or audio after the buffer is filled.

    3. Should I change the Mic Hz to a lower value (down from 98 GHz) in the Audio Midi System app?  I'm unclear from previous posts if this is the problem and what value to use.

    Many thanks for any help.

    -Todd

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 1 yr ago
    • Reported - view

    Update to 9.0.6 as 9.0.5 may not be Big Sur compatible.

    Todd Ehlers said:
    I've been recording lectures the last 4 months, and in the last weeks I started having this problem (I didn't have it before).  

     Can you tie it to a specific change if it's only in the last weeks?
    Settings? An update?

     

    Todd Ehlers said:
    The Apple Audio Midi setup app says the mic is working at 98GHz. 

     This doesn't look right. Please check. You may want to try 48kHz or 44.1kHz.

    For testing you really want to eliminate variables. To start with test using only the C920  Video and Audio and remove all other video and audio sources from the computer (eliminate Cam Link and Apogee) and just see how a single USB video/audio source with the same signal path (that's the C920).

    After doing that test, remove even the C920 and test with built in FaceTime webcam and Built in Mic. This will determine whether external sources are the issue.

    We are working on the next release which should fix sync issues. I can't give an exact date but it should be very soon.

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    • CraigS 

      Thank you.  I'll try tracking it down to a hardware item.

      Quick question:  Does the length of the recording (3 hours) potential influence if it goes out of sync .... or is there no logical reasons (e.g. no buffer overflow issue) Screenflow would be sensitive to this?

      Thanks,

      TE

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 1 yr ago
    • Reported - view
    Todd Ehlers said:
    Does the length of the recording (3 hours) potential influence if it goes out of sync

     Yes, the longer the more noticeable the drift. It may not be visible at all with short records. 

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  • Follow up note after trying many different configurations.

    The bottom line = NO SOLUTION TO the audio and video being out of sync with Screenflow v9.

    Tests tried:

    1. Many different cable connection configurations (with and without extension cables connected to the mic and web cam, and also trying different ports (USB2 or USB3 that the web cam is plugged into).

    2. Of particular importance - I most definitely reproduced the cable configuration I had several months ago when I didn't have problems for about 30 different screen recordings..

    3. I also tried a separate test where I changed the frequency of the Apogee Mic from the default of 96 GHz to 44 GHz.  Some other uses suggested this worked, but it made no difference aside from that the audio and video were in sync for the first 2 minutes, but then were out of sync after 10 mins.

    4. The only remaining possible solution is my upgrade to Mac OS Big Sur changed how Screenflow interacts with the computer hardware.

    These tests narrow down the problem to now being with Screenflow v9.0.8 (and it's compatibility with Big Sur v. 11.1, or visa versa).

    I hope the Telestream fixes this problem soon - there is nothing left to do on my end unless someone else has found a solution (?)

    Best wishes,

    Todd 

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    • CraigSModerator
    • Telestream Desktop Forum Moderator
    • CraigS
    • 1 yr ago
    • Reported - view
    Todd Ehlers said:
    These tests narrow down the problem to now being with Screenflow v9.0.8 (and it's compatibility with Big Sur v. 11.1, or visa versa).

     This is confusing. The current version of ScreenFlow is 9.0.6 and we believe this issue will be fixed in 9.0.7 (coming very soon).

    Please check your version number because the version number may confuse users.

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