FFmpeg notes

Links

https://ffmpeg.org/

The FFmpeg home page

https://trac.ffmpeg.org/wiki

The FFmpeg Bug Tracker and Wiki

https://git.ffmpeg.org/gitweb/ffmpeg.git

Browsable source code.

Docs

• Filter documentation

FFmpeg libopus codec documentation is here.

The following takes in some video and makes an Ogg/Opus file.

ffmpeg -i input -c:a libopus -b:a 128K -frame_duration 60 -metadata title="Some Title" -metadata artist="Some Artist" -bitexact output.opus

The following takes in a video and outputs a 96k audio/webm. Technically, audio/webm files can also have the .webm extension, but having it as .weba makes it easier to distinguish for a webserver trying to figure out the media/MIME type.

ffmpeg -hide_banner -i "$input" -vn -c:a libopus -b:a 96k -f webm output.weba

ffmpeg -i input.mp4 -vn -c:a libopus -b:a 96k -f caf output.caf

Concatenating Audio

Adapting the Concatenate page in the FFmpeg wiki, this is how I’d concatenate a bunch of MP3 files into a single Opus file. Note that it’s bash specific.

readarray -td '' argarray < <(printf -- '-i\0%s\0' *.mp3)
    ffmpeg "${argarray[@]}" -filter_complex "concat=n=$(( ${#argarray[@]} / 2)):v=0:a=1" -map_metadata -1 -bitexact -y output.opus

And here’s how you’d concatenate the audio of several files while stripping the video out:

myfiles=(*.webm)
readarray -td '' argarray < <(printf -- '-vn\0-i\0%s\0' "${myfiles[@]}")
ffmpeg "${argarray[@]}" -filter_complex "concat=n=${#myfiles[@]}:v=0:a=1" -map_metadata -1 -bitexact -y output.opus

This also works at generating audio/webm files.

TODO: I should figure out how to add chapter markers when concatenating. Kyle Howells has a blog post on adding chapters to MP4s that might be helpful for me here.

WebP

I kind of like WebP, which compresses images fairly well. I should investigate AVIF and JPEGXL later.

Here’s an example of converting a PNG (like a document) to WebP.

ffmpeg -hide_banner -i test1.png -f webp -quality 90 -preset text -compression 6 -y "test1.webp"

And here’s an example of taking an image from a pipe (a scanner) and saving it to a WebP:

scanimage --device "escl:http://192.168.1.XX:80" --format=png --resolution=300dpi --mode=color | ffmpeg -hide_banner -f image2pipe -c:v png -i - -f webp -quality 90 -preset text -compression 6 -y "output.webp"

WebM

WebM is a pretty cool format. Basically a limited Matroska that uses certain free codecs.

My screencaster tool records WebMs, though I noticed that these files aren’t seekable (since they’re essentially a concatenated stream). Doing the following simple thing reencodes it:

ffmpeg -i input.webm output.webm

This (on my system at least), reencodes it using libvpx-vp9, and shrunk a simple 5 second screencast from 375k to 47k.

TODO: I should check out the FFmpeg page on Encode/VP9

GIFs

Clément Bœsch has a pretty good blog post on making GIFs with FFmpeg. You should read that first.

Something like the following is what you can use to make stickers.

ffmpeg -i input.mp4 -vf "fps=8,scale=150:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse=dither=bayer:bayer_scale=5" -loop 0 -y output.gif

Metadata

ffmpeg -i input -metadata title="some title" -metadata somefield="some value" -c copy output

ffmpeg -i input.opus -map_metadata -1 -c:a copy -bitexact output.opus

Find encoder options

Like, here’s how to find which options work for the mjpeg (JPEG) encoder:

ffmpeg -hide_banner -h encoder=mjpeg

This outputs (truncated):

Encoder mjpeg [MJPEG (Motion JPEG)]:
    General capabilities: threads
    Threading capabilities: frame and slice
    Supported pixel formats: yuvj420p yuvj422p yuvj444p
mjpeg encoder AVOptions:
  -mpv_flags         <flags>      E..V....... Flags common for all mpegvideo-based encoders. (default 0)
     skip_rd                      E..V....... RD optimal MB level residual skipping
     strict_gop                   E..V....... Strictly enforce gop size
     qp_rd                        E..V....... Use rate distortion optimization for qp selection
     cbp_rd                       E..V....... use rate distortion optimization for CBP
     naq                          E..V....... normalize adaptive quantization

Pipe images

Use -f image2pipe with a video codec parameter (e.g. -c:v mjpeg or -c:v png) to input/output different formats. Another example:

<input1.png ffmpeg -hide_banner -f image2pipe -c:v png -i - -f image2pipe -c:v mjpeg -q:v 13 - > output1.jpg

Here, -q:v modifies the quality of the output JPEG.

Nix