biont Beginner

Sorry, mate, I'm here to report only. It will only take a minute for you to test: Muxer Properties > MP4 > Faststart=true, if the rendered file actually plays back – congratulations, you've fixed it. I'll be upgrading my Voukoder to a newer version, once the adjustable NVENC codec tag is implemented. Otherwise it's all good, don't wanna mess up anything in my current workflow.

Sure, everything's inside. When faststart (movflags 64) is enabled in the MP4 muxer, the resulting file is unreadable. The same file processed with standalone FFmpeg (-movflags +faststart) works fine. Maybe the post-processing step to move the moov atom is failing or corrupting the file.

Sorry, forgot to mention. It's MP4.

Hi, I get faulty file that doesn't open, when using NVENC and setting faststart to true in MP4 container in Voukoder Pro.

There is a practical compatibility issue with HEVC files encoded via NVENC. By default, Voukoder writes the hev1 codec tag, and such files do not play on iPhones. iOS expects the hvc1 tag – with it, the same file opens and plays without any issues. As a result, after encoding I have to do an extra remux step via ffmpeg just to change the tag using -tag:v hvc1, without re-encoding. This is purely a container-level fix, but it adds unnecessary friction to the workflow. It would be very helpful…