Something worth knowing before you convert anything: most converters re-encode by default, even when they don't need to.

Re-encoding decodes and rebuilds every frame. Do it once and you might not notice. Do it repeatedly, moving the same file between formats, and the degradation compounds. That's why a clip can look fine on your phone and noticeably soft when it finally hits a TV.

The alternative is remuxing — copying the existing video and audio streams into a new container without touching them. Zero quality loss, near-instant. FFmpeg does it with -c copy. The catch: it only works when the codec already fits the target format.

So when you're comparing converters, the questions that actually matter are:

Does it remux when it can, or always re-encode?

Does it preserve frame rate, aspect ratio, metadata and the audio stream?

Does it batch convert mixed formats in one pass, or one file at a time?

Is there a file size ceiling?

I've been testing Kernel Video Converter on a mixed-format job. Source support is broad — MP4, MKV, MOV, AVI, MXF, MTS, WEBM, WMV, DVD VOB and more — with outputs to MP4, AVI, MKV, MOV, plus audio extraction to MP3, M4A, WAV, AAC, OGG, WMA and AC3. It preserves frame rate, aspect ratio, metadata and audio stream on HD conversion, batch converts mixed formats in one operation, and has no file size restriction. Windows only.

One thing to know before downloading: it's not free software. The trial converts without limitation, but you can only view the first 15 seconds of the output — enough to confirm it handles your file, but full playback needs a license.

Anyone else here actually check output bitrate after converting, or do you just trust it looks right?
https://www.nucleustechnologies.com/video-converter/