# Membrane FFmpeg SWScale plugin
[](https://hex.pm/packages/membrane_ffmpeg_swscale_plugin)
[](https://hexdocs.pm/membrane_ffmpeg_swscale_plugin/)
[](https://circleci.com/gh/membraneframework/membrane_ffmpeg_swscale_plugin)
Plugin providing an element scaling raw video frames and performing pixel format conversions, using SWScale module of [FFmpeg](https://www.ffmpeg.org/) library.
It is a part of [Membrane Multimedia Framework](https://membrane.stream).
## Installation
Add the following line to your `deps` in `mix.exs`. Run `mix deps.get`.
```elixir
{:membrane_ffmpeg_swscale_plugin, "~> 0.16.0"}
```
The precompiled builds of the [ffmpeg](https://www.ffmpeg.org) will be pulled and linked automatically. However, should there be any problems, consider installing it manually.
### Manual instalation of dependencies
#### macOS
```shell
brew install ffmpeg
```
#### Ubuntu
```shell
sudo apt-get install ffmpeg
```
#### Arch / Manjaro
```shell
pacman -S ffmpeg
```
## Description
### Converter
Converter accepts raw video in any of the pixel formats specified in type [`Membrane.RawVideo.pixel_format_t()`](https://hexdocs.pm/membrane_raw_video_format/Membrane.RawVideo.html#t:pixel_format_t/0).
The element requires `Membrane.RawVideo` stream format on the input with `aligned: true` constraint, meaning that each buffer must contain exactly one raw video frame.
#### Converting pixel format
When creating the element you can specify a single option `format` defining the desired pixel format of the output.
`format` has to be [`Membrane.RawVideo.pixel_format_t()`](https://hexdocs.pm/membrane_raw_video_format/Membrane.RawVideo.html#t:pixel_format_t/0).
#### Scaling
Converter needs to receive stream format 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 Converter in the pipeline.
There are two options related to scaling, that can 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 has the size as specified in the options.
## Usage
Converting the pixel format of an encoded (using H.264 standard) video requires a parser and a decoder
because the `SWScale.Converter` performs conversion only on the raw, decoded video. The pipeline scales the video to the `640x640`
shape, changes the pixel format of the video to the `I422` format and reencodes it.
```elixir
defmodule Converting.Pipeline do
use Membrane.Pipeline
@impl true
def handle_init(_ctx, _options) do
structure = [
child(:file_src, %Membrane.File.Source{location: "/tmp/input.h264"})
|> child(:parser, Membrane.H264.Parser)
|> child(:decoder, Membrane.H264.FFmpeg.Decoder)
|> child(:converter, %Membrane.FFmpeg.SWScale.Converter{
output_height: 640,
output_width: 640,
format: :I422
})
|> child(:encoder, Membrane.H264.FFmpeg.Encoder)
|> child(:file_sink, %Membrane.File.Sink{location: "/tmp/output.h264"})
]
{[spec: structure], %{}}
end
end
```
## Copyright and License
Copyright 2021, [Software Mansion](https://swmansion.com/?utm_source=git&utm_medium=readme&utm_campaign=membrane)
[](https://swmansion.com/?utm_source=git&utm_medium=readme&utm_campaign=membrane)
Licensed under the [Apache License, Version 2.0](LICENSE)
