Marey.Tools.Video 0.7.0

Marey.Tools.Video

Video output for Marey, a dimensionally-typed visualization system for F#. The frame sequence is the product; the mux is a convenience over it.

#r "nuget: Marey.Tools.Video"

open Marey

let sequence =
    film |> Frames.write FramePass.Concurrent SkiaBackend.renderPng (FrameTarget.into "frames" ".png") 25.0

match Video.mux MuxOptions.Default sequence "shot.mp4" with
| MuxRan run when run.Succeeded -> printfn "encoded %d frames" run.FrameCount
| MuxUnavailable why -> printfn "%s" why      // the frames are still there, and this says so
| other -> printfn "%A" other

Marey.Plot renders an animation to a numbered directory on every core there is. This encodes that directory by running ffmpeg, which it looks for on PATH and reports — found, with its version, or absent with the sentence naming what to install.

Why a subprocess and not a binding

FFmpeg.AutoGen links libav* into your process: LGPL at best, GPL the moment the build carries x264, which puts a licence audit on everyone who references your project. A subprocess boundary keeps ffmpeg's licence ffmpeg's problem. The managed wrappers shell out anyway, so what they cost is a dependency and its opinions about temporary files, and what they buy is not writing one ProcessStartInfo.

This package therefore has no third-party dependency of any kind.

What is in it

• Video.mux, and Video.muxWith for a stated ffmpeg rather than the one on PATH. A missing encoder is MuxUnavailable — an outcome carrying what to install and the fact that the frames are still on disk — not an exception. A numbered directory is something every editor imports.
• Video.args, a pure function, so the exact command is a value you can print, diff or paste into a shell. Two positions in it are load-bearing and silent when wrong: -framerate before -i keeps every rendered frame, and the same number after -i resamples — 24 frames at 12 fps is 24 frames written correctly and 13 with the flag moved.
• Video.inspect, which decodes the result with ffprobe and says what is actually in it: codec, dimensions, frames counted rather than claimed, and the rate the container declares. Exit status is a weak gate — an encoder that wrote 13 of 24 frames exits zero.
• Reproducible containers. -fflags +bitexact and its companions strip the encoder=Lavf… and encoder=Lavc… tags that would otherwise name the ffmpeg build that wrote the file. VideoInfo.BuildTags is how you check, and it is empty.
• Video.check, which starts no process: leftover frames from a longer render (which ffmpeg -i frame-%05d.png would silently append as a tail), and odd pixel dimensions under a chroma-subsampled pixel format — read out of the first frame's own header, because a raster backend rounds an extent up.

Depends on Marey.Plot and Marey.Toolchain, and on nothing outside this repository.

• The guide, §20
• examples/video.fsx