[cornstalks]

That's the opposite of my experience. Depending on the decoder, lower resolutions may be more efficiently handled by the CPU instead of the hardware decoder (which is a decent chunk of silicon and takes extra power to use). But once you hit a certain resolution, the hardware decoder is pretty much always way more efficient than a software CPU decoder. Some well-implemented hardware decoders even handle low resolutions more efficiently.

My experience is largely focused on battery-powered mobile devices (Android/iOS), though.

[btdmaster]

To give a concrete example, VAAPI Haswell integrated graphics, peak CPU usage:

  mpv hardware H.264 1080p60: 3% CPU usage
  mpv software H.264 1080p60: 20% CPU usage

  mpv hardware H.264 4K60: 96% CPU usage
  mpv software H.264 4K60: 80% CPU usage

There comes a point of diminishing (or in this case, negative) returns. A bit more subjectively, the H.264 software rendering at 4K60 also felt smoother.

I'm using H.264 as it is hardware accelerated on this platform.

[cornstalks]

I don't think all Haswell chips support 4k H.264. That's one downside of hardware decoders: they have limits on what they support. I suspect the decoder is actually falling back to a software implementation to handle the bitstream since the hardware can't.

For example: https://www.avsforum.com/threads/no-hardware-4k-h264-decode-...

[zamadatix]

"Offloaded decoding takes more CPU than non-offloaded decoding" doesn't make any sense - clearly something else is going awry here.