Ffmpeg tools libx264 and libx265


So I’ve installed ffmpeg tools with view to converting some of my recordings into a smaller file size using libx265.

Unfortunately, the ffmpeg tools that I can install appears to be missing encodes?

When I try to run command

ffmpeg -i input -c:v libx265 -crf 28 -c:a aac -b:a 128k output.mp4

I get the error unknown encoder. Same problem with libx264. How do I go about fixing this.