I have some still shots from a security camera. I want to reduce the archive size while keeping the details. I use -qb for encoding rather than -crf because -crf blurs the moving objects.

I am experimenting with x265 (HEVC), using FFmpeg 4.2.2. The results are indeed impressive. If I wanted to encode a movie for normal watching, it is a great improvement versus x264 (I observe up to 60 % size, while having better quality).

However, the decoding takes a lot of processing power. I have a 7 years old Lenovo T540, which is still good for pretty much everything, but when I play a x265 video in VLC, it can't keep up and when a new object comes to a scene, the canvas turns gray with artefacts until the next I frame (I assume).

With -tune fastdecode this is fixed.

However: What is that I am giving up with fastdecode? I have found a few resources, but I assume that without the knowledge of x265 internals, I won't understand too much. It turns off these features (uses these flags) - see x265 docs:


This sounds like disabling quite a lot of key features of x265. Here is the x264 wiki page with some more explanation.

Question: When using fastdecode, doesn't x265 actually become worse than x264? AFAICT, default x264 preset uses these features, and yet I have no issues playing them. Is it due to HW support? If there is a high chance of dramatic future improvements in playback, then I would opt for the full-blown x265 encoding. Thanks.

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