How to implement multimedia encoding and decoding algorithms in C++?

How to implement multimedia encoding and decoding algorithms in C?

Abstract: Multimedia encoding and decoding are key technologies for audio and video processing. This article describes how to implement multimedia encoding and decoding algorithms in C and provides code examples.

Introduction
In modern multimedia applications, media encoding and decoding technology plays an important role. Multimedia coding converts original audio and video signals into compressed mathematical representations to reduce the resources required for storage and transmission. Decoding is the process of converting the compressed mathematical representation back to the original signal. This article will use C as an example to introduce how to implement multimedia encoding and decoding algorithms.

Implement audio encoding and decoding algorithms
To implement audio encoding and decoding algorithms in C, you can use open source libraries such as FFmpeg or GStreamer. The following is a sample code that uses the FFmpeg library for audio encoding and decoding:

#include <iostream>
#include <fstream>
#include <vector>

extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>
}

void encodeAudio(const char* inputFileName, const char* outputFileName, AVCodecID codecID) {
    AVFormatContext* formatContext = NULL;
    AVCodecContext* codecContext = NULL;
    AVCodec* codec = NULL;
    AVPacket* packet = NULL;
    AVFrame* frame = NULL;
    int ret;

    av_register_all();
    avcodec_register_all();

    formatContext = avformat_alloc_context();
    ret = avformat_open_input(&formatContext, inputFileName, NULL, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the input file" << std::endl;
        return;
    }

    ret = avformat_find_stream_info(formatContext, NULL);
    if (ret < 0) {
        std::cerr << "Error while finding stream information" << std::endl;
        return;
    }

    int audioStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &codec, 0);
    if (audioStreamIndex < 0) {
        std::cerr << "Error while finding audio stream" << std::endl;
        return;
    }

    codecContext = avcodec_alloc_context3(codec);
    ret = avcodec_open2(codecContext, codec, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the codec" << std::endl;
        return;
    }

    packet = av_packet_alloc();
    frame = av_frame_alloc();

    FILE* outputFile = fopen(outputFileName, "wb");

    while (av_read_frame(formatContext, packet) >= 0) {
        if (packet->stream_index == audioStreamIndex) {
            ret = avcodec_send_packet(codecContext, packet);
            if (ret < 0) {
                std::cerr << "Error while sending packet to the codec" << std::endl;
                break;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(codecContext, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    std::cerr << "Error while receiving frame from the codec" << std::endl;
                    break;
                }

                // 在这里可以对音频数据进行处理，如应用滤波器、增益等

                fwrite(frame->data[0], 1, frame->linesize[0], outputFile);
            }
        }

        av_packet_unref(packet);
    }

    fclose(outputFile);

    av_frame_free(&frame);
    av_packet_free(&packet);
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);
    avformat_free_context(formatContext);
}

void decodeAudio(const char* inputFileName, const char* outputFileName) {
    AVFormatContext* formatContext = NULL;
    AVCodecContext* codecContext = NULL;
    AVCodec* codec = NULL;
    AVPacket* packet = NULL;
    AVFrame* frame = NULL;
    int ret;

    av_register_all();
    avcodec_register_all();

    formatContext = avformat_alloc_context();
    ret = avformat_open_input(&formatContext, inputFileName, NULL, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the input file" << std::endl;
        return;
    }

    ret = avformat_find_stream_info(formatContext, NULL);
    if (ret < 0) {
        std::cerr << "Error while finding stream information" << std::endl;
        return;
    }

    int audioStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &codec, 0);
    if (audioStreamIndex < 0) {
        std::cerr << "Error while finding audio stream" << std::endl;
        return;
    }

    codecContext = avcodec_alloc_context3(codec);
    ret = avcodec_open2(codecContext, codec, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the codec" << std::endl;
        return;
    }

    packet = av_packet_alloc();
    frame = av_frame_alloc();

    FILE* outputFile = fopen(outputFileName, "wb");

    while (av_read_frame(formatContext, packet) >= 0) {
        if (packet->stream_index == audioStreamIndex) {
            ret = avcodec_send_packet(codecContext, packet);
            if (ret < 0) {
                std::cerr << "Error while sending packet to the codec" << std::endl;
                break;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(codecContext, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    std::cerr << "Error while receiving frame from the codec" << std::endl;
                    break;
                }

                // 在这里可以对音频数据进行处理，如应用滤波器、增益等

                fwrite(frame->data[0], 1, frame->linesize[0], outputFile);
            }
        }

        av_packet_unref(packet);
    }

    fclose(outputFile);

    av_frame_free(&frame);
    av_packet_free(&packet);
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);
    avformat_free_context(formatContext);
}

int main() {
    const char* inputFile = "input.wav";
    const char* encodedFile = "encoded.mp3";
    const char* decodedFile = "decoded.wav";
    
    // 编码音频
    encodeAudio(inputFile, encodedFile, AV_CODEC_ID_MP3);
    
    // 解码音频
    decodeAudio(encodedFile, decodedFile);
    
    return 0;
}

Implementing video encoding and decoding algorithms
Implementing video encoding and decoding algorithms in C, you can also use open source libraries such as FFmpeg or GStreamer . Below is a sample code for video encoding and decoding using the FFmpeg library:

#include <iostream>
#include <fstream>
#include <vector>

extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/opt.h>
#include }

void encodeVideo(const char* inputFileName, const char* outputFileName, AVCodecID codecID) {
    AVFormatContext* formatContext = NULL;
    AVCodecContext* codecContext = NULL;
    AVCodec* codec = NULL;
    AVPacket* packet = NULL;
    AVFrame* frame = NULL;
    int ret;

    av_register_all();
    avcodec_register_all();

    formatContext = avformat_alloc_context();
    ret = avformat_open_input(&formatContext, inputFileName, NULL, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the input file" << std::endl;
        return;
    }

    ret = avformat_find_stream_info(formatContext, NULL);
    if (ret < 0) {
        std::cerr << "Error while finding stream information" << std::endl;
        return;
    }

    int videoStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0);
    if (videoStreamIndex < 0) {
        std::cerr << "Error while finding video stream" << std::endl;
        return;
    }

    codecContext = avcodec_alloc_context3(codec);
    ret = avcodec_open2(codecContext, codec, NULL);    
    if (ret < 0) {
        std::cerr << "Error while opening the codec" << std::endl;
        return;
    }

    packet = av_packet_alloc();
    frame = av_frame_alloc();

    FILE* outputFile = fopen(outputFileName, "wb");

    while (av_read_frame(formatContext, packet) >= 0) {
        if (packet->stream_index == videoStreamIndex) {
            ret = avcodec_send_packet(codecContext, packet);
            if (ret < 0) {
                std::cerr << "Error while sending packet to the codec" << std::endl;
                break;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(codecContext, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    std::cerr << "Error while receiving frame from the codec" << std::endl;
                    break;
                }

                // 在这里可以对视频帧进行处理，如应用滤波器、调整亮度等

                fwrite(frame->data[0], 1, frame->linesize[0], outputFile);
                fwrite(frame->data[1], 1, frame->linesize[1], outputFile);
                fwrite(frame->data[2], 1, frame->linesize[2], outputFile);
            }
        }

        av_packet_unref(packet);
    }

    fclose(outputFile);

    av_frame_free(&frame);
    av_packet_free(&packet);
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);
    avformat_free_context(formatContext);
}

void decodeVideo(const char* inputFileName, const char* outputFileName) {
    AVFormatContext* formatContext = NULL;
    AVCodecContext* codecContext = NULL;
    AVCodec* codec = NULL;
    AVPacket* packet = NULL;
    AVFrame* frame = NULL;
    int ret;

    av_register_all();
    avcodec_register_all();

    formatContext = avformat_alloc_context();
    ret = avformat_open_input(&formatContext, inputFileName, NULL, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the input file" << std::endl;
        return;
    }

    ret = avformat_find_stream_info(formatContext, NULL);
    if (ret < 0) {
        std::cerr << "Error while finding stream information" << std::endl;
        return;
    }

    int videoStreamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0);
    if (videoStreamIndex < 0) {
        std::cerr << "Error while finding video stream" << std::endl;
        return;
    }

    codecContext = avcodec_alloc_context3(codec);
    ret = avcodec_open2(codecContext, codec, NULL);
    if (ret < 0) {
        std::cerr << "Error while opening the codec" << std::endl;
        return;
    }

    packet = av_packet_alloc();
    frame = av_frame_alloc();

    FILE* outputFile = fopen(outputFileName, "wb");

    while (av_read_frame(formatContext, packet) >= 0) {
        if (packet->stream_index == videoStreamIndex) {
            ret = avcodec_send_packet(codecContext, packet);
            if (ret < 0) {
                std::cerr << "Error while sending packet to the codec" << std::endl;
                break;
            }

            while (ret >= 0) {
                ret = avcodec_receive_frame(codecContext, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0) {
                    std::cerr << "Error while receiving frame from the codec" << std::endl;
                    break;
                }

                // 在这里可以对视频帧进行处理，如应用滤波器、调整亮度等

                fwrite(frame->data[0], 1, frame->linesize[0], outputFile);
                fwrite(frame->data[1], 1, frame->linesize[1], outputFile);
                fwrite(frame->data[2], 1, frame->linesize[2], outputFile);
            }
        }

        av_packet_unref(packet);
    }

    fclose(outputFile);

    av_frame_free(&frame);
    av_packet_free(&packet);
    avcodec_free_context(&codecContext);
    avformat_close_input(&formatContext);
    avformat_free_context(formatContext);
}

int main() {
    const char* inputFile = "input.mp4";
    const char* encodedFile = "encoded.mp4";
    const char* decodedFile = "decoded.avi";

    // 编码视频
    encodeVideo(inputFile, encodedFile, AV_CODEC_ID_H264);

    // 解码视频
    decodeVideo(encodedFile, decodedFile);

    return 0;
}

Conclusion
By using open source libraries such as FFmpeg, we can implement audio and video encoding and decoding algorithms in C. This article provides sample code to help readers better understand and apply these algorithms. Readers can modify and extend the code according to specific needs to meet their own multimedia processing needs.

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