Trimming a video with FFmpeg

FFmpeg provides a suite of command-line interface tools for working with audio and video files. It is free and open-source software that is available for a variety of operating systems, including Microsoft Windows, Linux, and macOS. If you wish to use it on a Microsoft Windows system, you can install it with the Windows Package Manager known as winget by opening a command prompt window and issuing the command winget install "FFmpeg (Essentials Build)". 

Microsoft Windows [Version 10.0.26100.7623]
(c) Microsoft Corporation. All rights reserved.

C:\Windows\System32>winget install "FFmpeg (Essentials Build)"
Found FFmpeg (Essentials Build) [Gyan.FFmpeg.Essentials] Version 8.0.1
This application is licensed to you by its owner.
Microsoft is not responsible for, nor does it grant any licenses to, third-party packages.
Downloading https://github.com/GyanD/codexffmpeg/releases/download/8.0.1/ffmpeg-8.0.1-essentials_build.zip
  ██████████████████████████████   101 MB /  101 MB
Successfully verified installer hash
Extracting archive...
Successfully extracted archive
Starting package install...
Command line alias added: "ffmpeg"
Command line alias added: "ffplay"
Command line alias added: "ffprobe"
Path environment variable modified; restart your shell to use the new value.
Successfully installed

C:\Windows\System32>

If you need to trim the beginning of a video file, such as a .mp4 file, you can do so using a command of the form ffmpeg -ss hh:mm:ss -i input.mp4 -c copy output.mp4 where you specify the point you wish the video to start in the form hh:mm:ss for hours, minutes, and seconds with -ss and input.mp4 is the file you wish to trim and output.mp4 is the name you wish to give to the trimmed file. E.g., if I have a video file, REC-0001-A.mp4, where I wish to discard audio and video up to the 3 minutes and 34 seconds mark in the file, I can use ffmpeg -ss 00:03:34 -i REC-0001-A.mp4 -c copy output1.mp4 to create a new file, output1.mp4, that omits the first 3 minutes and 33 seconds from the input file. Using the -c copy option copies the video/audio streams directly, which is fast but can be less accurate on keyframes.

C:\Users\moonp\Videos>ffmpeg -ss 00:03:34 -i REC-0001-A.mp4 -c copy output1.mp4
ffmpeg version 8.0.1-essentials_build-www.gyan.dev Copyright (c) 2000-2025 the FFmpeg developers
  built with gcc 15.2.0 (Rev8, Built by MSYS2 project)
  configuration: --enable-gpl --enable-version3 --enable-static --disable-w32threads --disable-a
  utodetect --enable-fontconfig --enable-iconv --enable-gnutls --enable-libxml2 --enable-gmp --e
nable-bzlib --enable-lzma --enable-zlib --enable-libsrt --enable-libssh --enable-libzmq --enable
-avisynth --enable-sdl2 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxvid --en
able-libaom --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enab
le-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libvidstab --enable-libvmaf --e
nable-libzimg --enable-amf --enable-cuda-llvm --enable-cuvid --enable-dxva2 --enable-d3d11va --e
nable-d3d12va --enable-ffnvcodec --enable-libvpl --enable-nvdec --enable-nvenc --enable-vaapi --
enable-openal --enable-libgme --enable-libopenmpt --enable-libopencore-amrwb --enable-libmp3lame
--enable-libtheora --enable-libvo-amrwbenc --enable-libgsm --enable-libopencore-amrnb --enable-l
ibopus --enable-libspeex --enable-libvorbis --enable-librubberband
  libavutil      60.  8.100 / 60.  8.100
  libavcodec     62. 11.100 / 62. 11.100
  libavformat    62.  3.100 / 62.  3.100
  libavdevice    62.  1.100 / 62.  1.100
  libavfilter    11.  4.100 / 11.  4.100
  libswscale      9.  1.100 /  9.  1.100
  libswresample   6.  1.100 /  6.  1.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 000001b033043400]
All samples in data stream index:id [2:3] have zero duration, stream set to be discarded by defa
ult. Override using AVStream->discard or -discard for ffmpeg command.
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'REC-0001-A.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.20.100
  Duration: 00:14:18.52, start: 0.000000, bitrate: 37520 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 3840x2160
, 37175 kb/s, 30 fps, 30 tbr, 90k tbn (default)
    Metadata:
      handler_name    : SStar Video
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 104 kb/s (de
fault)
    Metadata:
      handler_name    : SStar Audio
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](und): Data: none (ssmd / 0x646D7373)
    Metadata:
      handler_name    : SStarMeta
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Output #0, mp4, to 'output1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf62.3.100
  Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 384
0x2160, q=2-31, 37175 kb/s, 30 fps, 30 tbr, 90k tbn (default)
    Metadata:
      handler_name    : SStar Video
      vendor_id       : [0][0][0][0]
  Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 104 kb/s (default
)
    Metadata:
      handler_name    : SStar Audio
      vendor_id       : [0][0][0][0]
Press [q] to stop, [?] for help
[out#0/mp4 @ 000001b033046c40] video:2928211KiB audio:8253KiB subtitle:0KiB other streams:0KiB g
lobal headers:0KiB muxing overhead: 0.018641%
frame=19364 fps=1733 q=-1.0 Lsize= 2937011KiB time=00:10:44.43 bitrate=37335.1kbits/sspeed=57.7x
elapsed=0:00:11.17

C:\Users\moonp\Videos>

If the copy method freezes or starts at the wrong spot, you can re-encode to be more precise with a command such as ffmpeg -ss hh:mm:ss -i input.mp4 -c:v libx2x4 -c:a aac output.mp4 to re-encode the video for frame-accurate, perfect cuts. The process for re-encoding a video will take much longer, which is why using the -c copy method to trim a file in FFmpeg will complete much more quickly than trying to trim off the beginning of a video file with a program such as Kdenlive. Kdenlive offers many great audio/video editing features, but I found that trimming a few minutes from a video using that software took about 40 minutes for the rendering process to create the output file compared to about 9 seconds to trim the same video with FFmpeg using the -c copy option.

If you wish to start at a certain point and end after a specific duration, e.g., cut the first 10 seconds, then take the next 30 seconds, you can use a command such as ffmpeg -ss 00:00:10 -i input.mp4 -t 00:00:30 -c copy output.mp4 with -t 00:00:30 specifying the duration of the output file will be 30 seconds. Note: the output video might start slightly before or after the 10-second mark if it falls between keyframes.

Though placing -ss before -i is usually fater for input seeking, if the first few seconds in the output file are black, try plaing -ss after -i or use the re-encoding method.