H.265 (HEVC) compresses much better than H.264, but encoding it can fail in several ways.

Error 1: libx265 not found

Error message

Unknown encoder 'libx265'

FFmpeg 8.1 then also prints:

Error opening output files: Encoder not found

Cause

Your FFmpeg build doesn’t include libx265. This happens with self-built FFmpeg and with reduced distribution packages such as Fedora’s standard ffmpeg-free.

Ubuntu / Debian’s stock package is not one of them. The apt build includes libx265. Here are three entries in a row from the configuration: line of Ubuntu’s ffmpeg 6.1.1-3ubuntu5:

--enable-libwebp --enable-libx265 --enable-libxml2

If an apt install still gives Unknown encoder 'libx265', run which -a ffmpeg. Another FFmpeg (a self-built one, or a snap) is probably ahead of it on your PATH.

How to check

ffmpeg -buildconf | grep x265

If --enable-libx265 appears, your build has libx265. If nothing appears, it doesn’t.

How to fix

Ubuntu/Debian — install a full build:

# Ubuntu only: enable the universe repository (Debian has ffmpeg in main)
sudo add-apt-repository universe
sudo apt update && sudo apt install ffmpeg

If that still doesn’t work, use a static build (one program file with the libraries built in):

# Static build (john van sickle)
wget https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-amd64-static.tar.xz
tar -xf ffmpeg-release-amd64-static.tar.xz

macOS:

brew install ffmpeg

Use another HEVC encoder:

# NVENC (NVIDIA hardware encoding)
ffmpeg -i input.mp4 -c:v hevc_nvenc output.mp4

# VideoToolbox (macOS)
ffmpeg -i input.mp4 -c:v hevc_videotoolbox output.mp4

# QSV (Intel Quick Sync)
ffmpeg -i input.mp4 -c:v hevc_qsv output.mp4

Error 2: HEVC won’t play on iPhone or Apple devices

Symptom

An HEVC file made with FFmpeg won’t play on an iPhone or a Mac, or shows no thumbnail.

Cause

Apple devices expect the HEVC tag hvc1 (a code inside the file that names the format). FFmpeg writes hev1 by default.

How to fix

Add -tag:v hvc1:

ffmpeg -i input.mp4 -c:v libx265 -crf 28 -tag:v hvc1 output.mp4

Error 3: Profile or level issues

Error message

x265 [error]: main profile not supported, internal bit depth 10.
[libx265 @ 0000026dae75f7c0] Invalid or incompatible profile set: main.

How to fix

Match the profile to the bit depth:

Setting -profile:v main (an 8-bit profile) on 10-bit video causes this error. Set the bit depth with -pix_fmt too. -profile:v main10 alone does not make the output 10-bit; 8-bit video is still written as Main profile.

# Main profile (8-bit, best compatibility)
ffmpeg -i input.mp4 -c:v libx265 -crf 28 -pix_fmt yuv420p -profile:v main output.mp4

# Main10 profile (10-bit, for HDR)
ffmpeg -i input.mp4 -c:v libx265 -crf 28 -pix_fmt yuv420p10le -profile:v main10 output.mp4

Common level settings:

libx265 ignores -level:v. Set the level with level-idc inside -x265-params. Without high-tier=0, the stream is written as High tier.

# Specify an explicit level (improves device compatibility)
ffmpeg -i input.mp4 -c:v libx265 -crf 28 -x265-params level-idc=4.1:high-tier=0 output.mp4

Error 4: File size is larger than expected

If H.265 gives a larger file than H.264, your CRF value is probably too low. CRF sets the quality: a lower value means higher quality and a bigger file.

Use case CRF Notes
High-quality archive 18–22 About H.264 CRF 16–20
Balanced (recommended) 24–28 About H.264 CRF 22–26
Small-size priority 30–34 Visible quality loss 
# Balanced setup
ffmpeg -i input.mp4 -c:v libx265 -crf 26 -preset medium -c:a aac output.mp4

Error 5: Encoding is extremely slow

How to fix

Switch the preset to fast or faster:

ffmpeg -i input.mp4 -c:v libx265 -crf 26 -preset fast output.mp4

preset trade-offs (speed vs. quality):

ultrafast > superfast > veryfast > faster > fast > medium > slow > slower > veryslow
← faster, larger files                                 slower, smaller files →

Error 6: x265 log spam makes it look frozen

How to fix

x265 writes its own x265 [info] lines to stderr. In FFmpeg 8.1, -v quiet hides them too, and -stats keeps only the progress line (FFmpeg 8.0 and earlier also need -x265-params log-level=error):

ffmpeg -v quiet -stats -i input.mp4 -c:v libx265 -crf 26 output.mp4

Baseline H.265 Encoding Commands

# Basic (quality-first)
ffmpeg -i input.mp4 -c:v libx265 -crf 26 -c:a aac output.mp4

# Apple compatibility
ffmpeg -i input.mp4 -c:v libx265 -crf 26 -tag:v hvc1 -c:a aac output.mp4

# Speed-first
ffmpeg -i input.mp4 -c:v libx265 -crf 26 -preset fast -c:a aac output.mp4

Frequently Asked Questions

Why does HEVC fail in browsers?

It depends on the browser and the device. Safari plays HEVC from version 11. Chrome 107+ and Firefox 134+ (Windows; 136+ on macOS, 137+ on Linux) play it when the device can decode HEVC in hardware (on the GPU or a similar chip). For video on the web, convert to H.264, which all major browsers play. Safari plays AV1 only on devices with AV1 hardware decoding, such as iPhone 15 Pro.

My HEVC plays in VLC but not in Premiere — why?

Premiere imports HEVC (H.265) directly; it is on Adobe’s list of supported formats. That list mentions the Microsoft Store HEVC extension only for importing HEIF images on Windows. If a file still won’t open, convert it to H.264 with the command in the next answer. VLC plays it because it has its own HEVC decoder.

How do I quickly convert HEVC to H.264?

Run ffmpeg -i in.mp4 -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k out.mp4. CRF sets quality, not size, so the H.264 file won’t necessarily be close to the HEVC file’s size. In a test with FFmpeg 8.1 on a 10-second 1080p clip of Big Buck Bunny (CC BY 3.0), settings with almost the same VMAF (a video quality score) gave 4.94 MB for libx265 at CRF 25 and 7.12 MB for libx264 at CRF 23.

What is the difference between HEVC and H.265?

None. They are the same standard: H.265 is the ITU name and HEVC is the MPEG name. The file extension doesn’t change either.

Will I lose quality re-encoding HEVC to H.264?

A little. H.264 needs 30–50% more bitrate for the same visual quality. In a test with FFmpeg 8.1 on a 1080p clip of Big Buck Bunny, H.264 at CRF 20 and HEVC at CRF 22 got almost the same VMAF.

Primary source: trac.ffmpeg.org/wiki/Encode/H.265