Blender VSE Audio out-of-sync when animation (video) is rendered - audio

Question

Ok, so I found out that Blender has this really cool video-editing interface and I was beginning to love it. Until, I created this awesome project composition and when I exported the animation as a video file, the audio was out of sync :(.
Actual Problem
Audio is in-sync with video when the animation is played in Blender but is out-of-sync in the rendered video.
Solutions I tried out and failed
I used the 'Audio-Sync' option in the sequencer but that made no difference.
Then I thought that my scene audio frequency might have been an issue since it was initially 48kHz and my videos were at 24kHz, so I changed the scene audio frequency to 24kHz, this still failed to solve the issue.
Initially, I was combining videos with different frame rates and thought that might have been an issue (although animation played as expected in Blender), so I recreated the source videos to ensure all videos I was using in my project had the same frame rate, but this also did not work.
Someone online suggested exporting the video and audio separately and then combining them using a command-line tool like FFMPEG, this also failed.
What's really frustrating
This lag (audio is a few frames ahead of the video) is noticeable only in longer videos (>12 mins, my video is 1 hr long) suggesting a very small rendered rate difference between the video and the audio.
Also, note that the animation plays absolutely fine in Blender, so all I could figure out was that this was a rendering issue.
So if anyone figured this out please let me know. I am a noob in video/audio codecs so please forgive me if I used some incorrect nomenclature above.

Answer 1

I encountered this issue on OBS capture (a 13 minute clip) with Blender 2.93.3. OBS capture is constant framerate at 60 fps, I did try Handbrake conversion to 60 fps constant framerate also with no help. Workaround to solve the issue is to set Blender rendering fps to 59.94, sequencer shows audio track extending over video track but after render everything matches perfectly. Unfortunately you cannot edit the video in 59.94 fps mode, so you need to switch back to 60 fps for editing.
In case your video is 24 fps then use 23.98 fps preset and for 30 fps you can use the 29.97 fps preset.

Answer 2

May 2021. Blender v2.92.0 - I experienced the same as described out-of-sync problem with rendered videos that were over five minutes long. Source was as-is (3.6GB, 10mins) file from Canon EOS 5DMKII, which is an old camera, so pretty much any software can handle the encoding.
In Blender's preview mode everything looks in-sync. Audio and Video tracks are of the same length. I didn't even cut or merged any segments of the source video. I tried running rendering after a clean boot, gave Blender highest resource priority in Win10, allocated more memory to caching, etc. Source and output was on SSD. Rendered result still didn't match what GUI showed. Very frustrating, and a lot of wasted time.
What worked better for me is the following:
Change Video Codec to "FFmpeg video codec #1". This produces a lossless file that is about 27 times bigger (13.8GB for 10mins) than H.264 codec file (0.5GB). However, the audio remains in sync all the way through.
Use HandBrake open source video transcoder to convert FFmpeg file into H.264 (or H.265). End result produces a smallish-size file with A/V that is in sync.
This workaround is relatively painless and produces good-quality results because there's only a single lossy compression step. The time required to get to final file more than triples though. I believe the issue continues to be with the way H.264 rendering in Blender is implemented. I also experienced similar out-of-sync issues in ShotCut a year ago while working with cheap action cam H.265 files. I also found ShotCut to be less stable than Blender.

Answer 3

So after a lot of online searching, I did find an answer to fix this problem, but not in Blender. If you are like me and would like to use Blender for video editing and still get around the issue, then I found a workaround, but you need Shotcut for this. Shotcut is another great free and open-source video editor
Export the entire long video from Blender (the rendered video has desync issues as expected).
Open the video in Shotcut and detach the audio from it.
Use the audio properties to make very fine adjustments to the audio playback speed to suit your requirements (make fine adjustments until video and audio are in sync).
Follow the GIF attached.
(I am using a shorter video in the GIF but you get the idea)
Explanation
Blender has issues while rendering long videos and I noticed that the video is exported at 1.0x speed but the audio is sometimes faster (1.00400x or something like that) and hence the rendered video has audio not in sync with the video.
Another bad thing is that Blender does not really allow very fine playback speed adjustment just to the audio.
One trick is to adjust the pitch of the audio in Blender which in turn changes the playback speed but this is only allowed up to 2 decimal places (not what we want for long videos) and it makes the audio sound funny (since it actually changes the pitch).
Shotcut is a great tool that allows fine playback adjustment, and it also has a pitch compensation feature so that your pitch is kind of unaffected (since we don't want the characters to be sounding funny in our edited video).
Shotcut allows playback speed adjustment up to 6 decimal places.

Answer 4

I landed at this thread because of the same issue happening in a video that I have just finished. The "View animation CTRL F11" command starts an internal player that has sync issues with long videos. Opening the same video file on "Videos" in Fedora, it plays perfectly synchronized.