Are encoders the same regardless of hardware?

[seanmcnally]

Just a simple question as I'm trying to ponder the variability of encoding, even to the same format. For example, Nvidia's NVENC codec vs the x264 codec produce very different results, even though they're both encoding h.264 video.

So my question is, does hardware make a difference? Is the same video encoded with NVENC on two different Nvidia cards going to be encoded the same way? Will the video encoded on two different CPUs be the same if they're both using the same version of x264? Thanks.

[jagabo]

So my question is, does hardware make a difference?

Yes.

Is the same video encoded with NVENC on two different Nvidia cards going to be encoded the same way?

Only if they have the same encoder generation (and same settings, obviously).

Will the video encoded on two different CPUs be the same if they're both using the same version of x264?

Generally, yes. But there are some circumstances where there can be a difference. For example, x264 mulitithreads by breaking the frame up into rectangular tiles and each thread works on one tile. This reduces quality a bit. And the more threads the worse it gets. So a CPU with one thread will give better results than a CPU with 64 threads.