Inability to Sync Canon R5C S&F Slow-Mo Footage with Audio

I’m experiencing a long-standing issue in DaVinci Resolve Studio 19 when working with Canon R5C footage shot in Slow and Fast Motion mode.

The Canon R5C records video in XF-AVC Intra 4:2:2 10-bit at 119.88 fps (S&F Clip / Audio (WAV) mode), saved as .MXF files. These files embed a base frame rate of 59.94, and since the actual recorded frame rate is 119.88, they play back in slow motion. No usable audio is embedded—only a blank audio track. This affects how playback is interpreted in most NLEs. Audio is recorded separately as 59.94 fps .WAV files. Each video and audio file pair shares the same base filename and identical duration. However, the embedded timecode between the two does not align and drifts progressively out of sync. This may be a Canon firmware issue, but the result is that syncing automatically by timecode does not work.

Changing the clip’s frame rate to 119.88 in Clip Attributes corrects playback speed visually, but syncing by timecode still fails. I’ve confirmed the video and audio files are duration-matched.

Attempting to reconform them in Resolve using “loose filename match only” sometimes produces a correct sync, but the behavior is inconsistent. Roughly half of the clips sync properly, while the others are completely misaligned—for example, the audio may appear reversed, with the beginning aligned to the end of the clip. This inconsistency appears even when all IN/OUT points are cleared and both media and audio clips are batch reconformed from clean bins.

The only reliable method is to drag each audio and video clip pair to a timeline, align them manually by filename and clip extents, and link them. This is not scalable for shoots involving hundreds of clips or when footage needs to be culled efficiently. I’ve tried Resolve scripting using AutoSyncClips(video, audio, "timecode"), matching by base filename. The result is the same—since the embedded timecode is unreliable, scripting is ineffective, and there is no API-level access to sync based on filename, duration, or clip extents.

I’ve also attempted FFmpeg-based workflows to speed up the video and embed the audio before import. While this works, it requires re-encoding (e.g. to ProRes), which significantly increases file sizes and loses the structure, quality, and efficiency of Canon’s original XF-AVC .MXF encoding. MXF is an advanced container designed for broadcast standards, and Canon’s flavor of XF-AVC embeds additional metadata and GOP structure that cannot be replicated easily without their SDK or proprietary tools. The FFmpeg workaround is not viable for large-scale use due to file size and quality tradeoffs.

What I need is a reliable method to automatically sync external audio with S&F video clips inside the Media Pool. The most straightforward approach would be to match clips based on identical base filenames and exact clip durations. Each video and audio file is a unique one-to-one pair, and syncing by filename and duration would resolve the issue without relying on invalid timecode metadata.

Is anyone else shooting Canon R5C S&F motion and encountering this issue? Has anyone found a reliable method to sync external audio with these clips—preferably using Resolve-native tools, or any other effective solution?

System: MacBook Pro M3 Max, 64GB RAM, macOS 15.5
Version: DaVinci Resolve Studio 19
Camera: Canon EOS R5 C
Recording Mode: S&F Clip / Audio (WAV)
Video: XF-AVC Intra 4:2:2 10-bit, recorded at 119.88 fps with a base frame rate of 59.94 fps, saved as .MXF files
Audio: 59.94 fps .WAV, recorded separately

Thanks.

I'm confused.

You expect slow motion footage and real time audio to properly sync over time?

I’m looking for a technically viable way to sync the separately recorded R5C audio with its matching high-frame-rate video, when the footage is conformed to real-time playback (119.88 fps). This is not about syncing real-time audio to slow-motion playback. Has anyone found a reliable solution for this in Resolve?

Just trying to get it straight in my own head, you have a 120 fps timeline? And the Clip Attributes have been altered to play at 120 fps?

Yes, the timeline is set to 119.88 fps (or occasionally 59.94, depending on client specs), and Clip Attributes are always set to 119.88 fps to ensure real-time playback. The footage is recorded at 119.88 fps because some clients require deliverables with synced audio at normal speed, while also needing flexibility to use the same footage as slow-motion B-roll.

OK. Someone else may have to hep out here as I don't have any experience doing this.

My philosophy is that the real-time/slow-motion decision needs to be made on set. You shoot what you need for that shot.

(If a change from real-time to slow-motion is needed later, Optical Flow in Resolve is the way. If a change from slow-motion to real-time is needed, you're hosed.)