# Membrane FFmpeg SWScale plugin

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Plugin providing an element scaling raw video frames and performing pixel format conversions, using SWScale module of [FFmpeg]( library.

It is a part of [Membrane Multimedia Framework](

## Installation

Add the following line to your `deps` in `mix.exs`. Run `mix deps.get`.

	{:membrane_ffmpeg_swscale_plugin, "~> 0.10.0"}

You also need to have [FFmpeg]( library with development headers installed on your system.

## Description

### PixelFormatConverter
PixelFormatConverter accepts raw video in any of the pixel formats specified in type [`Membrane.RawVideo.pixel_format_t()`](
as input and is capable of producing output in any of these pixel formats.

When creating the element you need to specify a single option `format` defining the desired pixel format of the output.
The element requires `Membrane.RawVideo` caps on the input with `aligned: true` constraint, meaning that each buffer must contain exactly one raw video frame.

### Scaler
Scaler needs input in the YUV420p format, processes one frame at a time and requires getting caps with input video
width and height. To meet all requirements either `Membrane.RawVideo.Parser` or some decoder
(e.g. `Membrane.H264.FFmpeg.Decoder`) have to precede Scaler in the pipeline.

There are two options that have to be specified when creating the element:

- `output_width` - desired scaled video width.
- `output_height` - desired scaled video height.

Both need to be even numbers.

Scaling consists of two operations:

- scaling itself - resizing video frame with keeping original ratio. After that operation at least one of the
dimensions of the input frame match the respective dimension of the desired output size. The second one
(if does not match) is smaller than its respective dimension.
- adding paddings - if one dimension does not match after scaling, paddings have to be added. They are put on both
sides of the scaled frame equally. They are either above and below the frame or on the left and right sides of it.
It depends on the dimension that did not match after scaling.

The output of the element is also in the YUV420p format. It has the size as specified in the options.

## Sample usage

Scaling encoded (using H.264 standard) video requires parser and decoder because Scaler scales only raw video.

defmodule Scaling.Pipeline do
  use Membrane.Pipeline

  @impl true
  def handle_init(_) do
    children = [
      file_src: %Membrane.File.Source{location: "/tmp/input.h264"},
      parser: Membrane.H264.FFmpeg.Parser,
      decoder: Membrane.H264.FFmpeg.Decoder,
      scaler: %Membrane.FFmpeg.SWScale.Scaler{output_width: 640, output_height: 640},
      encoder: Membrane.H264.FFmpeg.Encoder,
      file_sink: %Membrane.File.Sink{location: "/tmp/output.h264"}

    links = [
      |> to(:parser)
      |> to(:decoder)
      |> to(:scaler)
      |> to(:encoder)
      |> to(:file_sink)

    {{:ok, spec: %ParentSpec{children: children, links: links}}, %{}}

## Copyright and License

Copyright 2021, [Software Mansion](

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Licensed under the [Apache License, Version 2.0](LICENSE)