AVC / H.264 Encoder

How to use Transcoder.Push to encode an AVC / H.264 elementary stream from raw YUV frames.

Video Input

As video input we use the foreman_qcif.yuv file from the AVBlocks Assets archive. After downloading and unzipping you will find foreman_qcif.yuv in the vid subdirectory.

Code

This code shows how you can encode raw uncompressed YUV frames into an H.264 stream. Two Transcoder objects are used, one to read the raw YUV frames from a file, and another to encode the raw frames to AVC / H.264 Annex B stream. The encoding is done via the Transcoder.Push method.

Initialize AVBlocks

static void EncodeH264Stream()
{
    Library.Initialize();

    EncodeH264Stream("foreman_qcif.yuv", "foreman_qcif.h264");

    Library.Shutdown();
}

Configure YUV Reader

static Transcoder CreateYUVReader(string inputFile)
{
    // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV input

    // MediaPin and VideoStreamInfo
    var yuvInPin = new MediaPin() {
        StreamInfo = new VideoStreamInfo() {
            StreamType = StreamType.UncompressedVideo,
            FrameRate = 30.0,
            FrameWidth = 176,
            FrameHeight = 144,
            ColorFormat = ColorFormat.YUV420,
            ScanType = ScanType.Progressive
        }
    };

    // MediaSocket
    var yuvInSocket = new MediaSocket() {
        StreamType = StreamType.UncompressedVideo,
        File = inputFile
    };

    yuvInSocket.Pins.Add(yuvInPin);

    // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV output
    // This is the same as the input, but no output file is set on the MediaSocket, 
    // because we want to pull frames one by one using Transcoder.Pull

    // MediaPin and VideoStreamInfo
    var yuvOutPin = new MediaPin() {
        StreamInfo = new VideoStreamInfo() {
            StreamType = StreamType.UncompressedVideo,
            FrameRate = 30.0,
            FrameWidth = 176,
            FrameHeight = 144,
            ColorFormat = ColorFormat.YUV420,
            ScanType = ScanType.Progressive
        }
    };

    // MediaSocket
    var yuvOutSocket = new MediaSocket() {
        StreamType = StreamType.UncompressedVideo,
    };

    yuvOutSocket.Pins.Add(yuvOutPin);

    // Create Transcoder
    var yuvReader = new Transcoder();
    yuvReader.Inputs.Add(yuvInSocket);
    yuvReader.Outputs.Add(yuvOutSocket);

    return yuvReader;
}

Configure AVC / H.264 Encoder

static Transcoder CreateH264Encoder(string outputFile, HardwareEncoder hardware)
{
    // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV input

    // MediaPin and VideoStreamInfo
    var yuvInPin = new MediaPin() {
        StreamInfo = new VideoStreamInfo() {
            StreamType = StreamType.UncompressedVideo,
            FrameRate = 30.0,
            FrameWidth = 176,
            FrameHeight = 144,
            ColorFormat = ColorFormat.YUV420,
            ScanType = ScanType.Progressive
        }
    };

    // MediaSocket
    var yuvInSocket = new MediaSocket() {
        StreamType = StreamType.UncompressedVideo
    };

    yuvInSocket.Pins.Add(yuvInPin);

    // Create VideoStreamInfo, MediaPin, and MediaSocket describing the H.264 output

    // MediaPin and VideoStreamInfo
    var h264OutPin = new MediaPin() {
        StreamInfo = new VideoStreamInfo() {
            StreamType  = StreamType.H264,
            FrameRate = 30.0,
            FrameWidth = 176,
            FrameHeight = 144,
            ColorFormat = ColorFormat.YUV420,
            ScanType = ScanType.Progressive
        }
    };

    // Enable \ disable hardware acceleration
    h264OutPin.Params.Add(Param.HardwareEncoder, hardware);

    // MediaSocket
    var h264OutSocket = new MediaSocket() {
        StreamType = StreamType.H264,
        File = outputFile
    };

    h264OutSocket.Pins.Add(h264OutPin);

    // Transcoder
    var h264Encoder = new Transcoder();
    h264Encoder.Inputs.Add(yuvInSocket);
    h264Encoder.Outputs.Add(h264OutSocket);

    return h264Encoder;
}

Open Transcoders

static void EncodeH264Stream(string inputFile, string outputFile)
{
    // Create a reader to simulate raw video frames. In reality you will likely
    // have a different raw video source, for example some kind of video capture device.
    Transcoder yuvReader = CreateYUVReader(inputFile);

    // Create a H.264 encoder. We will pass the raw video frames to it 
    // to encode them as AVC / H.264
    Transcoder h264Encoder = CreateH264Encoder(outputFile, HardwareEncoder.Auto);

    if (yuvReader.Open())
    {
        if (h264Encoder.Open())
        {
            EncodeH264Stream(yuvReader, h264Encoder);

            h264Encoder.Close();
        }

        yuvReader.Close();
    }
}

Call Transcoder.Pull and Transcoder.Push

static void EncodeH264Stream(Transcoder yuvReader, Transcoder h264Encoder)
{
    int inputIndex = 0;
    MediaSample yuvFrame = new MediaSample();

    while (true)
    {
        // Simulate raw frames
        // Each call to Transcoder.Pull returns one video frame.
        if (!yuvReader.Pull(out inputIndex, yuvFrame))
            break;

        // Pass the raw video frame to Transcoder.Push to encode it as AVC / H.264
        if (!h264Encoder.Push(0, yuvFrame))
            break;
    }

    h264Encoder.Flush();
}

Complete Program

using System;
using System.Linq;

using PrimoSoftware.AVBlocks;

namespace H264Encoder
{
    class Program
    {
        static Transcoder CreateYUVReader(string inputFile)
        {
            // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV input

            // MediaPin and VideoStreamInfo
            var yuvInPin = new MediaPin() {
                StreamInfo = new VideoStreamInfo() {
                    StreamType = StreamType.UncompressedVideo,
                    FrameRate = 30.0,
                    FrameWidth = 176,
                    FrameHeight = 144,
                    ColorFormat = ColorFormat.YUV420,
                    ScanType = ScanType.Progressive
                }
            };

            // MediaSocket
            var yuvInSocket = new MediaSocket() {
                StreamType = StreamType.UncompressedVideo,
                File = inputFile
            };

            yuvInSocket.Pins.Add(yuvInPin);

            // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV output
            // This is the same as the input, but no output file is set on the MediaSocket, 
            // because we want to pull frames one by one using Transcoder.Pull

            // MediaPin and VideoStreamInfo
            var yuvOutPin = new MediaPin() {
                StreamInfo = new VideoStreamInfo() {
                    StreamType = StreamType.UncompressedVideo,
                    FrameRate = 30.0,
                    FrameWidth = 176,
                    FrameHeight = 144,
                    ColorFormat = ColorFormat.YUV420,
                    ScanType = ScanType.Progressive
                }
            };

            // MediaSocket
            var yuvOutSocket = new MediaSocket() {
                StreamType = StreamType.UncompressedVideo,
            };

            yuvOutSocket.Pins.Add(yuvOutPin);

            // Create Transcoder
            var yuvReader = new Transcoder();
            yuvReader.Inputs.Add(yuvInSocket);
            yuvReader.Outputs.Add(yuvOutSocket);

            return yuvReader;
        }

        static Transcoder CreateH264Encoder(string outputFile, HardwareEncoder hardware)
        {
            // Create VideoStreamInfo, MediaPin, and MediaSocket describing the YUV input

            // MediaPin and VideoStreamInfo
            var yuvInPin = new MediaPin() {
                StreamInfo = new VideoStreamInfo() {
                    StreamType = StreamType.UncompressedVideo,
                    FrameRate = 30.0,
                    FrameWidth = 176,
                    FrameHeight = 144,
                    ColorFormat = ColorFormat.YUV420,
                    ScanType = ScanType.Progressive
                }
            };

            // MediaSocket
            var yuvInSocket = new MediaSocket() {
                StreamType = StreamType.UncompressedVideo
            };

            yuvInSocket.Pins.Add(yuvInPin);

            // Create VideoStreamInfo, MediaPin, and MediaSocket describing the H.264 output
    
            // MediaPin and VideoStreamInfo
            var h264OutPin = new MediaPin() {
                StreamInfo = new VideoStreamInfo() {
                    StreamType  = StreamType.H264,
                    FrameRate = 30.0,
                    FrameWidth = 176,
                    FrameHeight = 144,
                    ColorFormat = ColorFormat.YUV420,
                    ScanType = ScanType.Progressive
                }
            };

            // Enable \ disable hardware acceleration
            h264OutPin.Params.Add(Param.HardwareEncoder, hardware);
    
            // MediaSocket
            var h264OutSocket = new MediaSocket() {
                StreamType = StreamType.H264,
                File = outputFile
            };

            h264OutSocket.Pins.Add(h264OutPin);

            // Transcoder
            var h264Encoder = new Transcoder();
            h264Encoder.Inputs.Add(yuvInSocket);
            h264Encoder.Outputs.Add(h264OutSocket);

            return h264Encoder;
        }

        static void EncodeH264Stream(Transcoder yuvReader, Transcoder h264Encoder)
        {
            int inputIndex = 0;
            MediaSample yuvFrame = new MediaSample();

            while (true)
            {
                // Simulate raw frames
                // Each call to Transcoder.Pull returns one video frame.
                if (!yuvReader.Pull(out inputIndex, yuvFrame))
                    break;

                // Pass the raw video frame to Transcoder.Push to encode it as AVC / H.264
                if (!h264Encoder.Push(0, yuvFrame))
                    break;
            }

            h264Encoder.Flush();
        }

        static void EncodeH264Stream(string inputFile, string outputFile)
        {
            // Create a reader to simulate raw video frames. In reality you will likely
            // have a different raw video source, for example some kind of video capture device.
            Transcoder yuvReader = CreateYUVReader(inputFile);

            // Create a H.264 encoder. We will pass the raw video frames to it 
            // to encode them as AVC / H.264
            Transcoder h264Encoder = CreateH264Encoder(outputFile, HardwareEncoder.Auto);

            if (yuvReader.Open())
            {
                if (h264Encoder.Open())
                {
                    EncodeH264Stream(yuvReader, h264Encoder);

                    h264Encoder.Close();
                }

                yuvReader.Close();
            }
        }

        static void EncodeH264Stream()
        {
            Library.Initialize();

            EncodeH264Stream("foreman_qcif.yuv", "foreman_qcif.h264");

            Library.Shutdown();
        }

        static void Main(string[] args)
        {
            EncodeH264Stream();
        }
    }
}

How to run

Follow the steps to create a C# console application in Visual Studio but in Program.cs use the code from this article.

Copy the foreman_qcif.yuv file from the assets archive to bin/x64/Debug/net6.0 under the project’s directory.

Run the application in Visual Studio.