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H.265/HEVC Video Encoding Guide
This guide focuses on the encoder libx265 which can offer around 25–50% bitrate savings compared to H.264 video encoded with libx264, while retaining the same visual quality. These gains will be most pronounced at resolutions of 1080p and higher.
See HWAccelIntro for information on supported hardware H.265/HEVC encoders.
Getting ffmpeg with libx265 support
ffmpeg needs to be built with the
--enable-libx265 configuration flags and requires
x265 to be installed on your system. The Compilation Guides show you how to do that.
You can also download a static build, all of which bundle libx265.
You can list private options available in this encoder with
ffmpeg -h encoder=libx265.
Rate control modes
Similar to x264, the x265 encoder has multiple rate control algorithms, including:
- 1-pass target bitrate (by setting
- 2-pass target bitrate
- Constant Rate Factor (CRF)
In this guide we are going to focus on CRF and Two-Pass encoding, as 1-pass target bitrate encoding is not recommended.
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, except that maximum value is always 51, even with 10-bit support, so please read the H.264 guide for more info.
As with x264, you need to make several choices:
- Choose a CRF. CRF affects the quality. The default is 28, and it should visually correspond to libx264 video at CRF 23, but result in about half the file size. CRF works just like in x264, so choose the highest value that provides an acceptable quality.
- Choose a preset. The default is
medium. The preset determines compression efficiency and therefore affects encoding speed. Valid presets are
placebo. Use the slowest preset you have patience for. Ignore
placeboas it provides insignificant returns for a significant increase in encoding time.
- Choose a tune (optional). By default, this is disabled, and it is generally not required to set a tune option. x265 supports the following
fastdecode. They are explained in the H.264 guide.
ffmpeg -i input -c:v libx265 -crf 26 -preset fast -c:a aac -b:a 128k output.mp4
This example uses AAC audio at 128 kBit/s. This uses the native FFmpeg AAC encoder, but under AAC you will find info about more options.
This method is generally used if you are targeting a specific output file size and output quality from frame to frame is of less importance. This is best explained with an example. Your video is 10 minutes (600 seconds) long and an output of 200 MiB is desired. Since
bitrate = file size / duration:
(200 MiB * 8192 [converts MiB to kBit]) / 600 seconds = ~2730 kBit/s total bitrate 2730 - 128 kBit/s (desired audio bitrate) = 2602 kBit/s video bitrate
You can also forgo the bitrate calculation if you already know what final (average) bitrate you need.
For two-pass, you need to run
ffmpeg twice, with almost the same settings, except for:
- In pass 1 and 2, use the
-x265-params pass=2options, respectively.
- In pass 1, output to a null file descriptor, not an actual file. (This will generate a logfile that ffmpeg needs for the second pass.)
- In pass 1, you can leave audio out by specifying
For libx265, the
-pass option (that you would use for libx264) is not applicable.
ffmpeg -y -i input -c:v libx265 -b:v 2600k -x265-params pass=1 -an -f null /dev/null && \ ffmpeg -i input -c:v libx265 -b:v 2600k -x265-params pass=2 -c:a aac -b:a 128k output.mp4
As with CRF, choose the slowest
-preset you can tolerate, and optionally apply a
-tune setting. Note that when using faster presets with the same target bitrate, the resulting quality will be lower and vice-versa.
Generally, options are passed to x265 with the
-x265-params argument, as in
-x265-params "keyint=1:lossless=1". 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.
-x265-params lossless=1 option. Adding
-crf 0 is not required.
You can verify lossless encoding by looking for
x265 [info]: lossless compression ratio in the console output from your encoding command, or refer to the hash demuxer for verification.
-g 1 option for FFmpeg 4.3 and newer or if you're using a build from the git master branch. Older versions must use
Profiles can be set via the
-profile:v option, similar to libx264. See a list of available x265 profiles.
- x265 API documentation
- Netflix Tech Blog — A Large-Scale Comparison of x264, x265, and libvpx (link to paper)
- P. Hanhart et al., Subjective quality evaluation of the upcoming HEVC video compression standard (PDF)