Hardware Acceleration in the WebRTC Framework¶
WebRTC is a free open source project that provides real-time communication capabilities to browsers and mobile apps.
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.
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:
Camera setup: Connect a USB camera to the NVIDIA® Jetson™ device.
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.
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:
Enter this command to install pulseaudio:
$ sudo apt install pulseaudio
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 onlySdpVideoFormat
(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 fileHeader files: All WebRTC header files with their respective pathnames
video_loopback
: An application to test basic video loopback functionalitypeerconnection_client
: A client application that connects to a server and to other clientspeerconnection_server
: An application that creates a server and an interface to clientsmodule_test
: An encoder unit test applicationREADME
: A README file for applications andNvVideoEncoderFactory
.
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.