Pion MediaDevices

Go implementation of the MediaDevices API

mediadevices provides access to media input devices like cameras, microphones, and screen capture. It can also be used to encode your video/audio stream to various codec selections. mediadevices abstracts away the complexities of interacting with things like hardware and codecs allowing you to focus on building appilcations, interacting only with an amazingly simple, easy, and elegant API!

Install

go get -u github.com/pion/mediadevices

Usage

The following snippet shows how to capture a camera stream and store a frame as a jpeg image:

package main

import (
	"image/jpeg"
	"os"

	"github.com/pion/mediadevices"
	"github.com/pion/mediadevices/pkg/prop"

	// This is required to register camera adapter
	_ "github.com/pion/mediadevices/pkg/driver/camera" 
	// Note: If you don't have a camera or your adapters are not supported,
	//       you can always swap your adapters with our dummy adapters below.
	// _ "github.com/pion/mediadevices/pkg/driver/videotest"
)

func main() {
	stream, _ := mediadevices.GetUserMedia(mediadevices.MediaStreamConstraints{
		Video: func(constraint *mediadevices.MediaTrackConstraints) {
			// Query for ideal resolutions
			constraint.Width = prop.Int(600)
			constraint.Height = prop.Int(400)
		},
	})

	// Since track can represent audio as well, we need to cast it to 
	// *mediadevices.VideoTrack to get video specific functionalities
	track := stream.GetVideoTracks()[0]
	videoTrack := track.(*mediadevices.VideoTrack)
	defer videoTrack.Close()

	// Create a new video reader to get the decoded frames. Release is used 
	// to return the buffer to hold frame back to the source so that the buffer 
	// can be reused for the next frames.
	videoReader := videoTrack.NewReader(false)
	frame, release, _ := videoReader.Read()
	defer release()

	// Since frame is the standard image.Image, it's compatible with Go standard 
	// library. For example, capturing the first frame and store it as a jpeg image.
	output, _ := os.Create("frame.jpg")
	jpeg.Encode(output, frame, nil)
}

More Examples

• Webrtc - Use Webrtc to create a realtime peer-to-peer video call
• Face Detection - Use a machine learning algorithm to detect faces in a camera stream
• RTP Stream - Capture camera stream, encode it in H264/VP8/VP9, and send it to a RTP server
• HTTP Broadcast - Broadcast camera stream through HTTP with MJPEG
• Archive - Archive H264 encoded video stream from a camera

Available Media Inputs

Input	Linux	Mac	Windows
Camera	✔️	✔️	✔️
Microphone	✔️	✔️	✔️
Screen	✔️	✔️	✔️

By default, there's no media input registered. This decision was made to allow you to play only what you need. Therefore, you need to import the associated packages for the media inputs. For example, if you want to use a camera, you need to import the camera package as a side effect:

import (
	...
	_ "github.com/pion/mediadevices/pkg/driver/camera"
)

Available Codecs

In order to encode your video/audio, mediadevices needs to know what codecs that you want to use and their parameters. To do this, you need to import the associated packages for the codecs, and add them to the codec selector that you'll pass to GetUserMedia:

package main

import (
	"github.com/pion/mediadevices"
	"github.com/pion/mediadevices/pkg/codec/x264"      // This is required to use H264 video encoder
	_ "github.com/pion/mediadevices/pkg/driver/camera" // This is required to register camera adapter
)

func main() {
	// configure codec specific parameters
	x264Params, _ := x264.NewParams()
	x264Params.Preset = x264.PresetMedium
	x264Params.BitRate = 1_000_000 // 1mbps

	codecSelector := mediadevices.NewCodecSelector(
		mediadevices.WithVideoEncoders(&x264Params),
	)
	
	mediaStream, _ := mediadevices.GetUserMedia(mediadevices.MediaStreamConstraints{
		Video: func(c *mediadevices.MediaTrackConstraints) {},
		Codec: codecSelector, // let GetUsermedia know available codecs
	})
}

Since mediadevices doesn't implement the video/audio codecs, it needs to call the codec libraries from the system through cgo. Therefore, you're required to install the codec libraries before you can use them in mediadevices. In the next section, it shows a list of available codecs, where the packages are defined (documentation linked), and installation instructions.

Note: we do not provide recommendations on choosing one codec or another as it is very complex and can be subjective.

Video Codecs

x264

A free software library and application for encoding video streams into the H.264/MPEG-4 AVC compression format.

• Package: github.com/pion/mediadevices/pkg/codec/x264
• Installation:
  • Mac: brew install x264
  • Ubuntu: apt install libx264-dev

mmal

A framework to enable H264 hardware encoding for Raspberry Pi or boards that use VideoCore GPUs.

• Package: github.com/pion/mediadevices/pkg/codec/mmal
• Installation: no installation needed, mmal should come built in Raspberry Pi devices

openh264

A codec library which supports H.264 encoding and decoding. It is suitable for use in real time applications.

• Package: github.com/pion/mediadevices/pkg/codec/openh264
• Installation: no installation needed, included as a static binary

vpx

A free software video codec library from Google and the Alliance for Open Media that implements VP8/VP9 video coding formats.

• Package: github.com/pion/mediadevices/pkg/codec/vpx
• Installation:
  • Mac: brew install libvpx
  • Ubuntu: apt install libvpx-dev

vaapi

An open source API that allows applications such as VLC media player or GStreamer to use hardware video acceleration capabilities (currently support VP8/VP9).

• Package: github.com/pion/mediadevices/pkg/codec/vaapi
• Installation:
  • Ubuntu: apt install libva-dev

Audio Codecs

opus

A totally open, royalty-free, highly versatile audio codec.

• Package: github.com/pion/mediadevices/pkg/codec/opus
• Installation:
  • Mac: brew install opus
  • Ubuntu: apt install libopus-dev

Benchmark

Result as of Nov 4, 2020 with Go 1.14 on a Raspberry pi 3, mediadevices can produce video, encode, send across network, and decode at 720p, 30 fps with < 500 ms latency.

The test was taken by capturing a camera stream, decoding the raw frames, encoding the video stream with mmal, and sending the stream through Webrtc.

FAQ

Failed to find the best driver that fits the constraints

mediadevices provides an automated driver discovery through GetUserMedia and GetDisplayMedia. The driver discover algorithm works something like:

1. Open all registered drivers
2. Get all properties (property describes what a driver is capable of, e.g. resolution, frame rate, etc.) from opened drivers
3. Find the best property that meets the criteria

So, when mediadevices returns failed to find the best driver that fits the constraints error, one of the following conditions might have occured:

• Driver was not imported as a side effect in your program, e.g. import _ github.com/pion/mediadevices/pkg/driver/camera
• Your constraint is too strict that there's no driver can fullfil your requirements. In this case, you can try to turn up the debug level by specifying the following environment variable: export PION_LOG_DEBUG=all to see what was too strict and tune that.
• Your driver is not supported/implemented. In this case, you can either let us know (file an issue) and wait for the maintainers to implement it. Or, you can implement it yourself and register it through RegisterDriverAdapter
• If trying to use import _ github.com/pion/mediadevices/pkg/driver/screen note that you will need to use GetDisplayMedia instead of GetUserMedia

Failed to find vpx/x264/mmal/opus codecs

Since mediadevices uses cgo to access video/audio codecs, it needs to find these libraries from the system. To accomplish this, pkg-config is used for library discovery.

If you see the following error message at compile time:

# pkg-config --cflags  -- vpx
Package vpx was not found in the pkg-config search path.
Perhaps you should add the directory containing `vpx.pc'
to the PKG_CONFIG_PATH environment variable
No package 'vpx' found
pkg-config: exit status 1

There are 2 common problems:

• The required codec library is not installed (vpx in this example). In this case, please refer to the available codecs.
• Pkg-config fails to find the .pc files for this codec (reference). In this case, you need to find where the codec library's .pc is stored, and let pkg-config knows with: export PKG_CONFIG_PATH=/path/to/directory.

Roadmap

The library can be used with our WebRTC implementation. Please refer to that roadmap to track our major milestones.

Community

Pion has an active community on the Slack.

Follow the Pion Twitter for project updates and important WebRTC news.

We are always looking to support your projects. Please reach out if you have something to build! If you need commercial support or don't want to use public methods you can contact us at team@pion.ly

Contributing

Check out the contributing wiki to join the group of amazing people making this project possible

License

MIT License - see LICENSE for full text