How do I fix audio and video out of sync?
What causes audio and video to go out of sync?
There are a few common causes of audio and video falling out of sync:
Encoding errors during production can cause timing issues in the audio and video streams that lead to sync problems during playback. For example, an error during compression or multiple encodings may introduce desynchronization.[1]
Mismatched frame rates between the audio and video can also lead to sync drift over time as the streams play at slightly different speeds. The audio may have been encoded at a different frame rate than the video, causing gradual desync.[2]
Latency and buffering issues during playback can delay the audio or video stream and cause temporary sync problems. Network delays, an underpowered device, or software/driver issues may introduce varying lag.
Check your playback setup
Sometimes audio and video falling out of sync is due to an issue with your playback hardware or settings, rather than with the video file itself. Here are some troubleshooting steps to try:
Try a different HDMI cable. Old or faulty HDMI cables can cause sync issues, especially at high resolutions or frame rates. Swap the cable connecting your playback device to your display for a different high quality one.
Use direct connections instead of converters. Converters like HDMI-to-DVI add lag that can throw off AV sync. Connect your playback device directly to your display if possible.
Update display drivers. Outdated graphics drivers can lead to video lag and sync issues. Make sure you have the latest drivers for your playback device and display.
Restart playback devices. Restarting devices like media players, TVs, and game consoles can clear any software glitches leading to sync problems. Power cycle your playback chain to see if it helps.
Adjust encoding settings
One of the most common causes of audio/video sync issues is mismatched encoding settings between the audio and video streams. To avoid this:
- Match the audio sample rate to the video frame rate. For example, if the video is 29.97 fps, use an audio sample rate of 48000 Hz. This will ensure an equal number of audio samples per video frame.
- Use a constant frame rate for encoding. Variable frame rates can cause drift between audio and video.
- Increase the audio buffer size in the encoder settings. This allows the encoder to work ahead on the audio to match up with the video time stamps. A buffer of 1000+ ms is recommended.
Properly matching up audio and video encoding parameters is essential to keeping everything in sync. Refer to your encoding software documentation to locate these settings.
Sources:
https://studio.support.brightcove.com/general/references/best-practices-video-creating-transcoding-and-uploading-workflow.html
Use audio delay settings
Most video players like VLC, Windows Media Player, QuickTime, and others have an “audio delay” or “sync audio” option that allows you to adjust the timing of the audio track relative to the video. This is one of the easiest ways to fix out of sync issues.
When using the audio delay settings, it’s best to make small timing adjustments incrementally. For example, try adjusting the delay by 50 or 100 milliseconds at a time. After each adjustment, play a segment with dialog to test if the sync is correct. Keep slowly adjusting until the audio matches the lip movements of the video.
On VLC player, you can use the “J” and “K” keyboard shortcuts to nudge the audio earlier or later while a video is playing. This makes it easy to dial in the perfect sync.1
For phones/tablets, accessing the audio delay setting may require digging into the app’s settings menus. But once found, the process of tweaking the delay works the same as on desktop players.
Remux the audio and video
One effective way to fix audio and video being out of sync is to remux the audio and video streams into a new container file with adjusted timing on the audio track. This involves:
- Demuxing the media file into separate audio and video streams using a tool like MKVToolNix.
- Analyzing the audio offset and determining exactly how much the audio timing needs to be adjusted.
- Modifying the audio track start time and duration to realign it with the video.
- Remuxing the offset audio track with the original video into a new MK
Re-encode the file
One effective way to permanently fix audio and video sync issues is to re-encode the media file with the sync settings adjusted. This involves running the file through an encoding software like Handbrake or FFmpeg and specifying proper frame rates, audio delays, and encoding parameters.
When re-encoding, it’s important to match the source and output frame rates to avoid further sync drift. Using a constant frame rate like 23.976 or 29.97 fps is recommended. You may also want to use 2-pass encoding to ensure optimal quality and synchronization.
Within the encoder settings, you can directly specify an audio delay in milliseconds to line the audio up with the video track. Some encoders like Handbrake make this very easy to adjust during conversion.
The benefit of re-encoding is it bakes in the audio and video sync, correcting any drift problems. The drawback is it can reduce video quality, especially when using lossy compression like h.264. For best results, use the highest quality settings your hardware can handle.
Overall, re-encoding media is an effective solution to permanently resolve audio and video synchronization problems if done properly. Matching frame rates and dialing in the ideal audio delay during encoding can help get sound and video back in sync.
Use auto-sync tools
Many video processing and encoding apps like Handbrake have auto-sync features that can analyze your files and fix sync issues automatically.
Handbrake’s auto-sync works by analyzing the audio waveform and synchronizing it with the video track [1]. To use it, open Handbrake and add your video to the queue. Go to the Audio tab in the settings and check the “Auto audio sync” option. This will scan the file when encoding and shift the audio as needed to match the video.
You can also set up automatic file naming in Handbrake to avoid overwriting the original file. Go to Preferences > File Naming and enable “Automatically name output files”. Then set up a naming formula that works for your files [2].
Auto-sync can usually fix small timing drifts between audio and video tracks. It’s a quick and easy way to repair sync issues without having to manually adjust timing.
For live streams
One of the main causes of audio and video getting out of sync during live streaming is network issues causing packet loss or jitter. To help counteract this:
- Increase the buffer size on both the streaming server and player. This will help absorb more of the network jitter. Typically buffers of at least 4-5 seconds are needed for smooth streaming. Just keep in mind that larger buffers also increase latency.
- Use a dejitter buffer on the receiving player. Dejitter buffers temporarily store incoming packets and reorder them before sending to the media player. This helps smooth out network jitter. Many streaming protocols like HLS and MPEG-DASH have built-in dejitter buffers.
Additionally, using a wired Ethernet connection rather than WiFi can help reduce packet loss and jitter when streaming. If using WiFi, try moving closer to the router or access point. Upgrading to newer WiFi standards like 802.11ac can also help.1
When to seek professional help
If you have tried various troubleshooting steps and your audio and video still remain out of sync, it may be time to seek help from a professional. Some scenarios where you may need professional assistance include:
Source material has sync issues. If the original video file itself has sync problems, this can be difficult to fix on your own. Professionals may have access to specialized software or techniques to repair issues with the source footage (Source).
Problem persists across players and TVs. If you experience sync problems on multiple devices, there is likely an issue with the file encoding or container format. A professional can try re-encoding the file or remuxing the audio and video tracks to potentially resolve the problem.
In general, if you have exhausted the common troubleshooting fixes and the audio still remains out of sync, it’s best to seek help from an experienced video production professional or audio engineer. They can use specialized diagnostic tools and software to get to the root cause of the sync issue.
Preventing future sync issues
Following best practices during the video production and editing process can help prevent sync issues from occurring in the first place:
Follow encoding best practices – Use optimized encoder settings suited for your video footage to avoid introducing sync drift during encoding. Adhere to resolution, frame rate, and bitrate recommendations.
Use clean source material – Start with high-quality, properly synced audio and video sources before editing and encoding. This avoids compounding any existing sync issues.
Test playback before distribution – Thoroughly test videos on different devices before publishing online or delivering to clients. Confirm sync holds up during scrubbing, seeking, and streaming.
As covered in this LinkedIn article, following production and post-production best practices goes a long way in preventing frustrating out-of-sync issues down the line.
