Hardware Acceleration in the WebRTC Framework¶

WebRTC is a free open source project that provides real-time communication capabilities to browsers and mobile apps.

WebRTC architecture¶

A major feature of WebRTC is the ability to send and receive interactive HD videos. Fast processing of such videos requires hardware accelerated video encoding.

Currently the open source WebRTC project framework supports various software encoder types: VP8, VP9, and H264. NVIDIA integrates hardware accelerated H.264 encoding into the WebRTC encoding framework. This document uses the name NvEncoder to denote this feature.

Typical Buffer Flow¶

The following diagram shows a typical buffer flow in the hardware accelerated WebRTC encoding framework.

Typical buffer flow¶

A source delivers YUV frames, which the framework converts to I420 format and queues on the output plane of the encoder. The output plane buffers are sent to NvEncoder using proprietary NVIDIA low-level encoding libraries. NvEncoder returns filled encoded buffers on its capture plane.

The encoded buffers are sent for further processing as required by the application.

Application and Unit Test Setup¶

A README file in the WebRTC_r34.1_aarch64.tbz2 package contains additional information about for application usage and setup.

To set up and test the NvEncoder sample application¶

Video Loopback application: To run the application, enter this command:
```
$ ./video_loopback --codec H264 --width 1280 --height 720 --capture_device_index 0
```
Where:
- --codec specifies the encoding format. Hardware encoding currently supports only H.264.
- --width specifies the frame width.
- --height specifies the frame height.
- --capture_device_index specifies the index of /dev/video<x>.

If the WebRTC framework works correctly, the application displays the camera stream with the desired width and height. It scales if WebRTC detects frame drops.

Peer connection Client/Server application:
1. Camera setup: Connect a USB camera to the NVIDIA^® Jetson™ device.
2. Server setup: To start the peerconnection_client application on the Jetson platform, enter the command:
```
$ ./peerconnection_server
```
  This command starts the server on port 8888 with the default configuration.
3. Client setup: To start two instances of the peerconnection_client application on the Jetson platform, enter the commands:
```
$ ./peerconnection_client --autoconnect --server <Server.IP>
$ ./peerconnection_client --server <Server.IP> --autoconnect --autocall
```
  Each command starts an instance that connects a client to the server automatically. The second command uses the --autocall option to call the first available other client on the server without user intervention.
H.264 unit test for NvEncoder: Enter the command:
```
$ ./modules_tests --gtest_filter="TestNvH264Impl.*" --gtest_repeat=<num_of_iterations>
```
If the software on the Jetson device displays an error for pulseaudio:
1. Enter this command to install pulseaudio:
```
$ sudo apt install pulseaudio
```
2. Enter this command to start the pulseaudio daemon:
```
$ pulseaudio –start
```

Important Method Calls¶

NvEncoder is based on the NvVideoEncoderFactory class, defined in the header file:

webrtc_headers/modules/video_coding/codecs/nvidia/NvVideoEncoderFactory.h

This header file is in the package WebRTC_r34.1_aarch64.tbz2.

This section summarizes important calls to NvEncoder.

To create a hardware-enabled video encoder¶

Execute the method call:
```
std::unique_ptr<VideoEncoder> CreateVideoEncoder(const webrtc::SdpVideoFormat& format)
```
Where format specifies the desired encoding format. Currently only SdpVideoFormat (H.264) is supported.

The method creates and returns an NvVideoEncoder object for the specified format.

To query the video encoder¶

Execute the function call:
```
CodecInfo QueryVideoEncoder(const SdpVideoFormat& format)
```
Where format specifies the desired encoding format.

The function queries the video encoder and returns its codec information.

To get supported video formats¶

Execute the method call:

std::vector<SdpVideoFormat> GetSupportedFormats()

The method returns a vector of SdpVideoFormat objects with all formats supported by the encoder.

The WebRTC Package¶

The file WebRTC_r32.2.0_aarch64.tbz2 contains these files:

libwebrtc.a: A WebRTC library file
Header files: All WebRTC header files with their respective pathnames
video_loopback: An application to test basic video loopback functionality
peerconnection_client: A client application that connects to a server and to other clients
peerconnection_server: An application that creates a server and an interface to clients
module_test: An encoder unit test application
README: A README file for applications and NvVideoEncoderFactory.

The base commit ID for the library is 4db954eec11258d57e0d507b0436a183178dae22.

The commit ID corresponds to the OSS WebRTC project used for development. See this link for instructions to sync the OSS WebRTC project.

Limitations¶

Currently hardware acceleration supports only the H.264 encoder.

The video_loopback works only with the H.264 encoder.

USB Camera outputs buffers in YUY2 color format, but NVEncoder expects input in I420 or NV12 format, requiring a color conversion. This is currently done using the WebRTC framework on the CPU.