HON95-wiki/media/ffmpeg.md

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TODO

(Ignore this section.)

• -crf 23: Constant rate factor. Defaults to 23. Set to 0 for lossless video.

Resources

• steven2358: FFmpeg cheat sheet
• NVIDIA Developer Blog: NVIDIA FFmpeg Transcoding Guide

Installation

(Including V4L2 for Linux distros.)

• Linux (Ubuntu/Debian): sudo apt install ffmpeg v4l-utils
• Linux (Arch): sudo pacman -S ffmpeg v4l-utils
• Windows: Download binaries from some FFmpeg mirror site.

General Usage

Devices

Linux

• See the the Video4Linux 2 (V4L2) page for more info about managing devices.
• List devices: v4l2-ctl --list-devices
  • Cameras often provide multiple /dev/video<n> for the same device, only one of them provides the correct video feed.
• Show current device info: v4l2-ctl -<n> --all (for /dev/video<n>)
  • E.g. the pixel format and resolution is what is currently configured for the device.

Windows

• View devices: ffmpeg -list_devices true -f dshow -i dummy

View

• View video feed: ffplay <dev-or-url>
  • For some reason this often uses a limited framerate and resolution or high delay for me.

Recording

• Record stream to file, automatically split every X seconds, restart if the stream is unavailable:
  • Script: while true; do ffmpeg -hide_banner -loglevel error -i http://localhost:5555/ -c copy -map 0 -f segment -segment_time $((5*60)) -segment_format mp4 -strftime 1 "%Y-%m-%d_%H-%M-%S.mp4"; sleep 1; done
• Record time lapse at 10x speed without audio:
  • Command: ffmpeg -i http://localhost:5555/ -filter:v "setpts=0.1*PTS" -an out.mkv

Specific Usage

Concatenate Video Files

Useful e.g. to recombine video files for recorders which automatically splits the recording.

1. ffmpeg -f concat -safe 0 -i <(for f in ./*.MP4; do echo "file '$PWD/$f'"; done) -c copy output.MP4
   • For lexicographically sorted files ending in .MP4.

Speed Up/Slow Down Video, but Keep All Frames

Useful e.g. to change the framerate of a video-only timelapse video.

See: Speeding up/slowing down video (FFmpeg)

1. Convert to raw bitstream:
   • H.264: ffmpeg -i input.mp4 -map 0:v -c:v copy -bsf:v h264_mp4toannexb raw.h264
   • H.265: ffmpeg -i input.mp4 -map 0:v -c:v copy -bsf:v hevc_mp4toannexb raw.h265
2. Generate new video: ffmpeg -fflags +genpts -r <fps> -i raw.h264 -c:v copy output.mp4 (for desired frame rate fps)

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