Hardware-accelerated H.265 encoding in your browser

CRF (Constant Rate Factor) in x265 works similarly to x264: lower values mean higher quality and larger files. CRF 18 is near-lossless visually. CRF 23 is the x265 default and produces good quality for streaming and archive. CRF 28 is suitable for web delivery where file size is the priority. For comparison, CRF 23 in H.265 is roughly equivalent to CRF 18 in H.264 in terms of visual quality at nearly half the file size.

H.265 uses more complex coding tools (CTUs, more prediction modes, additional compression passes) that require significantly more CPU computation per frame. At equivalent quality settings, x265 typically takes 3–10x longer to encode than x264. In the browser (WASM), this is even more pronounced as there is no hardware acceleration. For long files, consider running the encoder overnight or using a native tool for time-critical work.

H.265 support has grown significantly but is not universal. It is natively supported on all Apple devices (iOS 9+, macOS 10.13+), Windows 10/11 with HEVC codec installed, Android 5+, and most modern Smart TVs. It is not natively supported in Firefox (royalty concerns) and some older browsers. For maximum compatibility in distribution, H.264 is still safer. H.265 is best suited for archive storage and delivery to known-compatible devices.