x265 is the dominant open-source HEVC encoder — the H.265 counterpart of the famous x264. Developed initially by MulticoreWare with community contributions, x265 has been the reference open-source HEVC implementation since the codec shipped in 2013, and remains the standard against which commercial HEVC encoders are measured. If you encode HEVC and you're not running x265, you're either running a hardware encoder (faster, slightly lower quality) or a commercial encoder that licenses x265's core somewhere in its pipeline.
The technical design follows the x264 playbook. Preset spectrum from ultrafast to placebo trades speed for compression — medium is the everyday default, slow and veryslow are the high-quality production settings, ultrafast is for live streaming. CRF rate control (default value 28 for x265 vs 23 for x264, because HEVC's quality-per-bit is higher) is the standard quality-driven encoding mode. Psy-RD perceptual tuning keeps texture detail and noise that pure mathematical optimisation would have smoothed away. HDR support is mature — Main 10 profile, BT.2020 colour, PQ and HLG transfer functions, HDR10 and Dolby Vision metadata all work out of the box.
For a product team, x265 is the go-to encoder for HEVC VOD libraries — better quality at the same bitrate than any hardware HEVC encoder, mature, well-documented, integrated with FFmpeg via libx265. The downside is the same as any software encoder: it's slow. Encoding 4K HDR at slow preset can take hours per hour of source. For VOD that's fine (encode once, serve millions of times); for live and high-volume, hardware encoders (NVENC, Quick Sync, VideoToolbox) take over despite the small quality gap. x265 is licensed under GPL with a commercial licence available from MulticoreWare for closed-source software shipments.
