My situation:

  1. Transcoding 1080p bluray videos to HEVC. Audio untouched;
  2. My rig is old (pre-2012) and to speed up the process I'm using --preset ultrafast;
  3. From x265 documentation, I understand that video quality is independent of the preset used. And the slower the preset, the better the compression ratio it seems;
  4. I'm using FFmpeg.

My Reasoning:

  1. I want to start converting to HEVC now because the codec is good enough for me and the space saving is phenomenal;
  2. I've seen people reporting a 35GB video compressed to 1GB or so with crf=18 and --preset veryslow. It sounds ludicrous but an experiment of my own shows about 40% additional space saving between presets ultrafast and veryslow.

The Question:

When I get a new rig with a more capable CPU (Skylake or later, I hear), is it possible for me, to "re-compress" my HEVC videos using eg. --preset veryslow, without quality loss due to encoding a second time?

1 Answer 1


In strict mathematical terms, no.

In terms of maintaining an acceptable image quality, yes. If you use CRF 18 and a preset like ultrafast now, you should be able to get a smaller acceptable file with preset veryslow later on.

  • Ahh too bad. Upon testing a longer clip, the size reduction is around 20%. I can live with that I guess. Thanks for the quick answer!
    – Yifeng Mu
    Dec 11, 2015 at 8:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.