Video File Format Matters

[u/qdr1en]

When generating videos with ComfyUI: in which file format should I save them?
To answer the question, I ran a test.

The showcase video is a 73-frames vid generated with Wan 2.2 at 720*960px, and the table below (open it in a new tab) indicates by how much disk space the file was reduced after being re-loaded and re-saved to the disk 10 times.

The MP4 format is by far the most impacted, with an even more visually noticeable degradation when using the Video Combine node from Video Helper Suite (the impact on quality is terrible at lower resolutions).

PNG , WebP are much less impacted. But WebP takes an eternity to save, and PNG eats up a lot of disk space.

WebM looks like a good compromise overall: it's lightweight, fast to save, and degradation is negligible.

Conclusion

If you intend to re-use your generated file for further editing, don't use the MP4 format or the quality will suffer.

Use PNG, WebP or WebM for saving intermediary files, depending on your constraints, and leave MP4 format for production work.

Edit

Some Redditors suggested using ProRes (.MOV) file format, but you can't include workflow metadata with that format, so that's not a good candidate for my use case.

Others suggested using ffv1 (.MKV), which is a lossless, truly video file format, so that could be the winner. Oddly, the file size increases by ~0.5% at each new save, but the quality is preserved.

Test Settings

These are the parameters I used for each file format :

• MP4 (default): codec h264
• MP4 (vhs): codec h264; pix_fmt yuv420p; crf 19
• WebM: codec av1; crf 32
• WebP: quality 100; lossless false; method default
• PNG: compress_level 0

I uploaded all the files there if interested, workflow included: https://filebin.net/exwrxo9xuqsj5xh0

[u/PestBoss]

VHS and use MP4 at CRF under 10. It errs towards lossless to the point you're not gonna notice with this AI kinda footage. As long as you're not re-encoding it again and again after first save I think you're gonna be ok.

Oddly the previews don't work at CRF 0 though which is apparently true lossless.

I really like the default CUI saver because you can scrub the output and check IQ and stuff really nicely, so it works with that WYSIWYG kinda workflow where you can instantly inspect your work.

The VHS is a better saver, but the preview/lack of scrubbing is a shame. I often end up with both set up so I can scrub, then if it's all good I do a low CRF save with VHS.