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vt-enc: FFmpeg VideoToolbox frontend in Bash
(github.com)
Icon base by Caro Asercion under CC BY 3.0 with modifications to add a gradient
You need VideoToolbox for this particular tool because it calls the VideoToolbox library from within FFmpeg in order to encode the video.
"Why do I need x264 to encode H.264 in FFmpeg?" is essentially what you're asking. FFmpeg needs VideoToolbox support to work with my tool.
If you're asking why I chose to use VideoToolbox in the first place, it was because I want this to be a macOS-specific tool with very fast encoding speeds at decent fidelity per bit. Hardware accelerated video encoding is one way to make this happen.