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ffmpeg: Unknown encoder 'libx264' (Encoder not found)

verified onenvironmentlocal · windows 10.0.26200 arm64 · GNU bash 5.3.15 (Git Bash) · ffmpeg version 9.0.2-full_build-www.gyan.devupdated 2026-10-20
tool
FFmpeg
exit code
8
versions
FFmpeg 5 – 9
os
linux, macos, windows

Unknown encoder 'x' followed by Encoder not found means ffmpeg has no encoder with that name. Either the name is misspelled, or the library behind it (libx264, libfdk_aac, libsvtav1 …) was not compiled into your ffmpeg. List the encoders your build actually has with ffmpeg -encoders.

Reproduce the error

bash
ffmpeg -hide_banner -loglevel error -f lavfi -i testsrc=duration=1 -c:v libnotreal -y out.mp4 2>&1 | sed 's/@ 0x\?[0-9a-f]*/@ …/g' ; exit "${PIPESTATUS[0]}"

Output · exit 8

[vost#0:0 @ …] Unknown encoder 'libnotreal'
[vost#0:0 @ …] Error selecting an encoder
Error opening output file out.mp4.
Error opening output files: Encoder not found

ffmpeg 9 exits with status 8 here; the memory address after @ changes on every run and is shortened.

Find the right name

bash
ffmpeg -hide_banner -encoders 2>/dev/null | grep -E ' (libx264|libx265|libvpx-vp9|libsvtav1|libopus|aac) '

Output

 V..... libsvtav1            SVT-AV1(Scalable Video Technology for AV1) encoder (codec av1)
 V....D libx264              libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (codec h264)
 V....D libx264rgb           libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 RGB (codec h264)
 V....D libx265              libx265 H.265 / HEVC (codec hevc)
 V....D libvpx-vp9           libvpx VP9 (codec vp9)
 A....D aac                  AAC (Advanced Audio Coding)
 A....D libopus              libopus Opus (codec opus)

The first column shows V for video and A for audio encoders.

Common fixes

You asked forIf it is missing, try
libx264 (H.264)a full build; or h264_nvenc / h264_qsv / h264_videotoolbox / h264_mf for hardware encoding
libx265 (HEVC)a full build; or hevc_nvenc / hevc_videotoolbox
libfdk_aacthe native aac encoder (-c:a aac)
libmp3lamea build with LAME; MP3 has no native encoder
vp9the encoder is called libvpx-vp9

Sources

Related pages

errors · ffmpeglibx264: width not divisible by 2 / height not divisible by 2libx264 rejects odd sizes with yuv420p: width not divisible by 2 (101x101). Scale to even sizes with scale=trunc(iw/2)*2:trunc(ih/2)*2 or use scale=-2:720.compat · ffmpegWhich codec in which container? MP4, WebM, MKV, MOV with FFmpegCodec and container compatibility tested with FFmpeg 9: H.264 and AAC fit MP4 and MKV but not WebM, which accepts only VP8, VP9, AV1, Vorbis and Opus.cheat sheets · ffmpegFFmpeg cheat sheet: convert, cut, scale, extract and inspectFFmpeg cheat sheet: inspect files with ffprobe, change containers, encode H.264, cut without re-encoding, scale, extract audio, make GIFs and thumbnails.