Transcoding x265 to x264

[therock003]

What is the recommended method to get this done quick and easy with optimal results

[LigH.de]

Current libavcodec based converters (using either ffmpeg, or plugins like FFMS2 and L-SMASH Works for AviSynth) can decode HEVC. So you will have a wide choice of converters. Chosing sane x264 options is your own responsibility, though. As you may already know, every conversion to a lossy format will decrease the quality further, only enough bitrate can make the loss less obvious (e.g. CRF encoding with a small factor, possibly 18 or less).

[therock003]

I dont really care, its only meant for playback on legacy devices coupled with old CRT-TVs. The original file will remain on storage. How much time will a laptop with a celeron cpu take for a 20-40 min video clip?

[LigH.de]

"Old CRT-TV" means only SD resolutions; so, depending on your preferred speed preset, it should be possible in playback time, probably even a bit faster.

"Legacy devices" may have to be discussed more in detail. They may require additional limiting parameters for compatibility.

Try TEncoder for batch processing of many files. It can run several conversions in parallel. But your Celeron may have only few CPU cores, and x264 works multi-threaded too, so that may exhaust your CPU if you try too many. And laptop CPUs may get throttled when they get too hot. Laptops are in general not a recommendable video conversion system.