# `FFix.Command.Mapping`
[🔗](https://github.com/akash-akya/ffix/blob/v0.2.0/lib/ffix/command/mapping.ex#L1)

An output's choice of source and encoding.

`FFix.Encoder` helpers and `FFix.stream_copy/1` create mappings for you.
`FFix.output/3` wraps bare streams in mappings using FFmpeg's default encoding.
Use `new/2` when building mappings directly or reusing an encoder configuration.

A mapping has a `source`, an `encoding`, and an optional output-local `name`.
Encoding is an `FFix.Encoder` configuration, `:copy`, or `nil` for FFmpeg's
defaults. See `FFix.Command.Output` for names and option callbacks.

## Encoding several tracks

A mapping of `FFix.audio(input, :all)` can create several audio tracks. The
same encoding applies to every selected track. Different settings need
separately indexed selections:

    alias FFix.Encoder
    source = FFix.input("interview.mkv")

    output =
      FFix.output([
        FFix.stream_copy(FFix.audio(source, :all)),
        Encoder.libx264(FFix.video(source, 0), crf: 20),
        Encoder.libx264(FFix.video(source, 0), crf: 28)
      ], "qualities.mkv")

    FFix.command(output)

Both video settings follow their respective mappings, even though the audio
selection's track count is unknown. FFix uses video-relative option scopes
in this case. When every mapping selects one stream, it uses absolute output
indexes. Indexes restart for each destination.

Within a media type, broad selections must share the same encoding policy
and options. Mixing all-audio copy with an individually encoded audio track
is ambiguous; select each audio track explicitly instead. Whole-input and
raw-string queries have unknown media, so layouts containing them support
leaving every mapping unconfigured or copying every mapping.

Reusing a direct input stream creates another output use with its own
encoding. To reuse a filtered stream, first branch it with
`FFix.Filter.split/2` or `FFix.Filter.asplit/2`.

# `t`

```elixir
@type t() :: %FFix.Command.Mapping{
  encoding: FFix.Encoder.t() | :copy | nil,
  name: atom() | nil,
  source: FFix.Command.source()
}
```

# `new`

```elixir
@spec new(FFix.Command.source(), FFix.Encoder.t() | :copy | nil) :: t()
```

Pairs a source with an encoder configuration, `:copy`, or FFmpeg's defaults (`nil`).

    encoder = FFix.Encoder.new("libx264", crf: 20)
    FFix.Command.Mapping.new(video, encoder)

Returns a mapping for `FFix.output/3`. Graph connectivity and stream-copy
compatibility with filtering are checked when assembling the command.

---

*Consult [api-reference.md](api-reference.md) for complete listing*