Compose a command with the builder¶

afmpeg.Command is a declarative description of a media job for the ffmpeg-wasi engine — a sequence of inputs, an optional filtergraph, and a sequence of outputs. It is use-case-agnostic: it models the structure of a job, so it expresses any workflow (transcode, scale, overlay, concat, thumbnail, audio extract, …). JobSpec() renders it to the engine's job spec; RunJob runs it.

There are two equally valid ways to build one.

As a struct — explicit, inspectable data¶

Fill the struct directly when you want full control (it's copyable and serialisable — a pipeline can come from YAML/JSON):

cmd := afmpeg.Command{
    Inputs:        []afmpeg.Input{{Path: "in.mkv"}},
    FilterComplex: "[0:v]scale=1280:-2[vout]",
    Outputs: []afmpeg.Output{{
        Path:       "out.mp4",
        Map:        []string{"[vout]"},
        VideoCodec: "libx264",
        Options:    map[string]string{"crf": "23", "movflags": "+faststart"},
    }},
}

With NewCommand — functional options¶

cmd := afmpeg.NewCommand(
    afmpeg.WithInput("bg.mp4"),
    afmpeg.WithInput("logo.png"),
    afmpeg.WithFilterComplex("[0:v][1:v]overlay=10:10[v]"),
    afmpeg.WithOutput("out.mp4",
        afmpeg.Map("[v]"), afmpeg.VideoCodec("libx264"), afmpeg.WithOption("crf", "23")),
)

Both forms produce the same Command.

Run it¶

res, err := rt.RunJob(ctx, fs, cmd) // sugar for rt.Run(ctx, fs, string(spec)) from cmd.JobSpec()
if err != nil {
    return err
}
if res.ExitCode != 0 {
    return fmt.Errorf("engine failed: %s", res.Stderr)
}
// Structured results (process status, a probe's info) come back on res.Stdout.

JobSpec() emits {op:"process", inputs, filter, outputs}. The filter is the full ffmpeg filter_complex (the engine parses it with libav); each output's Options map becomes the encoder options. See obtain a module for the ffmpeg-wasi release.

Encoder options¶

Any encoder setting goes in an output's Options map (struct) or via WithOption (builder) — nothing is blocked:

// a single-frame thumbnail
cmd := afmpeg.NewCommand(
    afmpeg.WithInput("in.mp4"),
    afmpeg.WithFilterComplex("[0:v]thumbnail[v]"),
    afmpeg.WithOutput("thumb.png", afmpeg.Map("[v]"), afmpeg.WithOption("frames:v", "1")),
)

Notes¶

• Pixel/sample format, output framerate, and duration live in the filtergraph (e.g. format=yuv420p, fps=30, trim) — the engine derives the container from the output path and the pixel/sample format from the graph + encoder.
• A higher-level workflow (a "reel", a thumbnail sheet, …) is your code composed on this builder — afmpeg ships no opinionated workflow types.