mp3 timing off with original movie

Hi All,

I really need help. I’be been recording multichannel mp4s recently, then opening them in audacity (selecting both tracks), simply editing out any coughing or background noise then exporting to mp3 and importing into the movie in place of the original track but recently I have found that after importing the exported mp3 in the sound is out of sync from the original track. I can see the original sound waves and when I play it it is perfectly in sync with the video but the exported mp3 is out of sync, and even more so for longer videos.

Even if I import the mp4 into audacity, edit/change nothing in the track and export it, when it it is imported the track is off and out of sync…

What am I doing wrong? This is the same unedited mp4…

Is there a setting I need to turn off?

The video people do have one oddity. Most video sound has a sample rate of 48000. Audacity defaults to the Audio CD rate of 44100. What happens if you do everything at 48000?

Audacity > Preferences > Quality > Sampling.

It shouldn’t make any difference, but it might.

Also see the sample rate reading in the lower left of the Audacity work window.


Also, it makes my teeth hurt when somebody goes through an MP3 conversion for no reason. MP3 is a compressed format that creates sound damage and you can’t stop it. The fewer MP3 steps in a project the better.


I think the problem is “timing glitches” in the original MP4. The more compressed files seem to be more prone to this. i.e. It seems to happen more often with MPEG-4 or MOV files than with MPEG-2, and DV-AVI seems to be pretty-much immune.

Sometimes, I’ve solved it by transcoding the original audio/video file to a different (usually slightly higher) bitrate or to a completely different format. But, that’s a lossy process even at a higher bitrate.

I have a program called Womble MPEG Video Wizard that has a “fix timestamps” feature (which sometimes works), but I think it’s no longer available, it’s not free, and it might only work with MPEG-2.

BTW - It’s best if you can export to WAV (or another lossless format) to minimize the number of times the audio is lossy-compressed.

If you must use lossy compression MP3 will add a few milliseconds of silence to the beginning of the file so you may have to slightly re-adjust the timing after loading the audio into your video editor. That’s a constant delay so it can be fixed and it doesn’t get worse with longer files.

MP4 audio (M4A or AAC) is more immune to accumulated damage than MP3. I believe there is a little delay (beginning silence) added to MP4 audio too but the decoder might automatically remove it.

I ran into a similar problem when trying to sync an MP3 from Audacity with a MOV file that was exported from Lightwave 3D animation. (Scroll to bottom of thread to see the final solution)

For some reason, Lightwave 3D misinterpreted the number of frames in the MP3 file, which threw off the timing when used as a reference for the lipsync. The solution is to use a WAV file instead. I don’t know if an Audacity-generated MP3 file is somehow different, or if the format itself lends to sync troubles, but it’s possible that the MP3 is being misinterpreted by your video editing software.

Even if I import the mp4 into audacity, edit/change nothing in the track and export it, when it it is imported the track is off and out of sync…

This part of the post suggests it goes wrong even without the MP3 step in the middle, but still. MP3 is terrible format to use in production. MP3’s full family name is MPEG1, Layer 3. It’s part of an old video format and was never intended for sound work divorced from its video base.


Thanks for your replies. I am using OBS to record 2 audio tracks (game sounds & mic) the end result is to upload to YouTube. I use Audacity to silence sections where I am coughing or clearing my throat. OBS is set up to record the audio at 4100 bit rate. So you’re saying tell OBS to output to WAV, edit the audio with audacity and do my video edits on iMovie (I only know how to use iMovie right now).

Please confirm I’ve understood correctly?

In iMovie, detach the audio from the video (if necessary) so you have three separate tracks - one video and two audio. See if you can mute the video and game-sounds tracks to export just your voice as a WAV file. If muting doesn’t work, make a COPY of the iMovie project, detach audio from video, then delete the video and game-sounds audio track so that all that remains is your voice track. Export a WAV of that and take it into Audacity to edit the silences.

Then, open the iMovie project with the three original tracks (one video, two audio) and add a new blank audio track at the bottom and import the edited WAV file. Is it the same length as the original? If so, you should be good to go, so you can delete (or, safer, mute) the original voice track (unmute the other two if necessary) and export the MP4.

Note the project sample rate in the lower-left corner of Audacity - that’s the rate it will use when exporting. It should default to 44100, so you might as well stick with that since that’s where OBS started out.

The problem with iMovie is that it merges the 2 audio tracks from the video so when you detach it it shows as one track… so I cannot do what you’re asking me. When I import the edited audacity file it is always slightly shorter.

Can you please refine your answer as iMovie merges the 2 audio tracks and cannot seperate them.

If you do a Google search on something like - OBS separate audio tracks - you will get thousands of hits that show you how to get separate audio tracks out of OBS.

This one looks like a comprehensive tutorial, but if it doesn’t cover your needs, check out the other search results.

I don’t know iMovie, but it seems like the problem can be fixed in OBS during the original recording session. For recordings that are already done with just one audio track, I don’t know how to fix that.