FFmpeg and H.265 Encoding Guide
H.265 (also known as HEVC) offers 50-75% more compression efficiency compared to H.264 video, while retaining the same visual quality. ffmpeg has support for HEVC encoding using the x265 encoder. Note: libx265 is under heavy development. The API may change.
Getting ffmpeg with libx265 support
In order to obtain a copy of ffmpeg with libx265 support, you need to build it yourself, adding the --enable-libx265 configuration flag, with x265 being installed on your system.
You can also download a static build, all of which bundle libx265.
Similar to x264, the x265 encoder has multiple rate control algorithms, including:
- 1-pass constant bitrate (by setting -b:v)
- 2-pass constant bitrate (see H.264#twopass)
- Constant Rate Factor (CRF)
In this guide we are going to focus on CRF encoding.
Constant Rate Factor (CRF)
Use this mode if you want to retain good visual quality and don't care about the exact bitrate or filesize of the encoded file. The mode works exactly the same as in x264, so please read the H.264 guide for more info.
In this example, we will use the following settings:
- default CRF of 28. The CRF of 28 should visually correspond to libx264 video at CRF 23, but result in about half the file size.
- medium preset. The preset determines how fast the encoding process will be – at the expense of compression efficiency. Put differently, if you choose ultrafast, the encoding process is going to run fast, but the file size will be larger when compared to medium. The visual quality will be the same. Valid presets are ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow and placebo.
- AAC audio at 128 kBit/s. This uses the ffmpeg-internal encoder, but under AAC you will find info about more options.
ffmpeg -i input -c:v libx265 -preset medium -crf 28 -c:a aac -b:a 128k output.mp4
Generally, options are passed to x265 with the -x265-params argument. For fine-tuning the encoding process, you can therefore pass any option that is listed in the x265 documentation. Keep in mind that fine-tuning any of the options is generally not necessary, unless you absolutely know what you need to change.