Which is better for lossless x264 compression: Ultrafast or Veryslow?

[Guernsey]

I was using an FFMPEG option to make my video lossless but when I searching for commands, I found that you could utilize presets for compression. My question which option is favorable for lossless compression? Should I leave it as is or should I use a preset? I am looking to preserve every aspect of the video with only a few artifacts.

[poisondeathray]

I was using an FFMPEG option to make my video lossless but when I searching for commands, I found that you could utilize presets for compression. My question which option is favorable for lossless compression? Should I leave it as is or should I use a preset? I am looking to preserve every aspect of the video with only a few artifacts.

lossless compression means no artifacts compared to the original, not "few" artifacts

veryslow preset lossless compression will give you slightly better compression ratio than ultrafast, at the expense of being slower to encode. They both have identical quality because they are lossless.

[jagabo]

Generally, the higher the preset the more compression you'll get. But how much more depends on the nature of the video. And that additional compression may not be worth the additional processing time (and won't be possible for realtime video capture). Real world video (VHS for example) doesn't get much more compression. Some edge cases like slideshows, Powerpoint presentations, computer rendered cartoons, etc. may get significantly more. You should compress some representative samples at different presets and see how the file size varies.

Also, be sure you aren't going through any color format changes before the compression. For example, converting YV24 to YV12 will lose color resolution, before you compress the video losslessly. If you want to restore the original YV24 you won't be able to. You will only be able to losslessly restore the YV12 that was given to the encoder.

I ran some quick tests on a 720x576 ffmpeg huffyuv 4:2:0 VHS avi cap:

Preset      fps    MB
-----------------------
Ultrafast   2031   591
Superfast    526   522
Veryfast     461   523
Medium       178   517
Versyslow     39   516
Placebo       12   516

[Guernsey]

So if I go higher I will get faster encoding but at the cost of compression?

[Selur]

Yes, the encoding will still be lossless and presets are just a tradeoff between speed and size.