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xav

★ 79 Open GitHub ↗

Elixir wrapper over FFmpeg for reading and decoding audio and video data

// repository documentation

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# Xav

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Elixir wrapper over FFmpeg for reading audio and video files.

See an interview with FFmpeg enthusiast:  https://youtu.be/9kaIXkImCAM

## Installation

Make sure you have installed FFMpeg (ver. 4.x - 7.x) development packages on your system
(see [here](INSTALL.md) for installation one-liners) and add Xav to the list of your dependencies:

```elixir
def deps do
  [
    {:xav, "~> 0.11.0"},
    # Add Nx if you want to have Xav.Frame.to_nx/1
    {:nx, ">= 0.0.0"}
  ]
end
```

## Controlling FFmpeg log output

FFmpeg's underlying libraries (`libavcodec`, `libswscale`, ...) print to `stderr` at the `AV_LOG_INFO` level by default. This is usually fine but can produce informational noise such as

```
[swscaler @ 0x1490a0000] No accelerated colorspace conversion found from yuv420p to rgb24.
```

when `libswscale` falls back to a generic colorspace conversion path. These are not errors — decoded frames are bit-exact — but they can clutter test output and logs.

You can raise the threshold from Elixir:

```elixir
Xav.set_log_level(:error)
```

Or set it once at application start by configuring your application env:

```elixir
# config/runtime.exs
config :xav, ffmpeg_log_level: :error
```

`Xav.Application` reads this on boot and applies it before your supervision tree starts. Valid atoms are `:quiet`, `:panic`, `:fatal`, `:error`, `:warning`, `:info`, `:verbose`, `:debug`, and `:trace`. An integer FFmpeg level is also accepted.

Note that `av_log_set_level/1` is process-global — changing the level affects every `libav*` call made from the current OS process, not just the reader that triggered the change.

## Usage

Decode

```elixir
decoder = Xav.Decoder.new(:vp8, out_format: :rgb24)
{:ok, %Xav.Frame{} = frame} = Xav.Decoder.decode(decoder, <<"somebinary">>)
```

Decode with audio resampling

```elixir
decoder = Xav.Decoder.new(:opus, out_format: :flt, out_sample_rate: 16_000)
{:ok, %Xav.Frame{} = frame} = Xav.Decoder.decode(decoder, <<"somebinary">>)
```

Read from a file:

```elixir
r = Xav.Reader.new!("./some_mp4_file.mp4")
{:ok, %Xav.Frame{} = frame} = Xav.Reader.next_frame(r)
tensor = Xav.Frame.to_nx(frame)
Kino.Image.new(tensor)
```

Read from a camera:

```elixir
r = Xav.Reader.new!("/dev/video0", device?: true, out_format: :rgb24)
{:ok, %Xav.Frame{} = frame} = Xav.Reader.next_frame(r)
tensor = Xav.Frame.to_nx(frame)
Kino.Image.new(tensor)
```

Speech to text:

```elixir
{:ok, whisper} = Bumblebee.load_model({:hf, "openai/whisper-tiny"})
{:ok, featurizer} = Bumblebee.load_featurizer({:hf, "openai/whisper-tiny"})
{:ok, tokenizer} = Bumblebee.load_tokenizer({:hf, "openai/whisper-tiny"})
{:ok, generation_config} = Bumblebee.load_generation_config({:hf, "openai/whisper-tiny"})

serving =
  Bumblebee.Audio.speech_to_text_whisper(whisper, featurizer, tokenizer, generation_config,
    defn_options: [compiler: EXLA]
  )

# Read a couple of frames.
# See https://hexdocs.pm/bumblebee/Bumblebee.Audio.WhisperFeaturizer.html for default sampling rate.
frames =
    Xav.Reader.stream!("sample.mp3", read: :audio, out_format: :flt, out_channels: 1, out_sample_rate: 16_000)
    |> Stream.take(200)
    |> Enum.map(fn frame -> Xav.Frame.to_nx(frame) end)

batch = Nx.Batch.concatenate(frames)
batch = Nx.Defn.jit_apply(&Function.identity/1, [batch])
Nx.Serving.run(serving, batch) 
```

## Development

To make `clangd` aware of the header files used in your project, you can create a `compile_commands.json` file. 
`clangd` uses this file to know the compiler flags, include paths, and other compilation options for each source file.

### Install bear

The easiest way to generate `compile_commands.json` from a Makefile is to use the `bear` tool. `bear` is a tool that records the compiler calls during a build and creates the `compile_commands.json` file.

You can install `bear` with your package manager:

- __macOS__: brew install bear
- __Ubuntu/Debian__: sudo apt install bear
- __Fedora__: sudo dnf install bear

### Generate compile_commands.json

After installing bear, you can run it alongside your make command to capture the necessary information.

```bash
bear -- mix compile
```

xav

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