Adobe Media Encoder - (PAID) - MAC / WINDOWS - https://www.adobe.com/ca/products/media-encoder.html
Handbrake - (FREE) - MAC / WINDOWS / LINUX - https://handbrake.fr/
VLC - (FREE) - MAC / WINDOWS / LINUX - https://www.videolan.org/
Apple Quicktime - (FREE) - MAC / WINDOWS - https://support.apple.com/downloads/quicktime - limited (no choice of in / out or codec, and limited deimensions) but fine for getting stuff to h264 (1920 x 1080 or 1280 x 720 or 640 x 480 / 360 - will recognise aspect ratio)
MIRO - (FREE) - MAC / WINDOWS / LINUX - http://www.mirovideoconverter.com/
DIVX Convertor - (FREE) - MAC - https://www.divx.com/the-amazing-divx-converter/
Video Convertor For Mac - (trial / PAID) - MAC - https://www.appgeeker.com/video-converter-for-mac.html
AVI Demux - (FREE) - MAC / WINDOWS / LINUX - http://avidemux.sourceforge.net/download.html
these will be ok if you have an older OS like High Sierra
MPEG Streamclip - (FREE) - MAC / WINDOWS - http://www.squared5.com/ - DOESNT WORK ON OS CATALINA OR NEWER
FFMpeg X - (FREE) - MAC - https://www.ffmpegx.com/ - DOESNT WORK ON OS CATALINA OR NEWER
- download here