ffmpeg MP4转h264 cpp代码

以下是使用FFmpeg将MP4视频转换为H.264视频的C++代码示例：

#include <iostream>
extern "C" {
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
}
using namespace std;

int main(int argc, char* argv[]) {
    AVFormatContext* inputFormatContext = nullptr;
    AVCodecContext* inputCodecContext = nullptr;
    AVCodec* inputCodec = nullptr;
    AVPacket inputPacket;
    AVFrame* inputFrame = nullptr;

    AVFormatContext* outputFormatContext = nullptr;
    AVCodecContext* outputCodecContext = nullptr;
    AVCodec* outputCodec = nullptr;
    AVPacket outputPacket;
    AVFrame* outputFrame = nullptr;

    const char* inputFilePath = "input.mp4";
    const char* outputFilePath = "output.h264";

    // Open input file
    if (avformat_open_input(&inputFormatContext, inputFilePath, nullptr, nullptr) != 0) {
        cerr << "Failed to open input file: " << inputFilePath << endl;
        return -1;
    }

    // Retrieve stream information
    if (avformat_find_stream_info(inputFormatContext, nullptr) < 0) {
        cerr << "Failed to retrieve input stream information" << endl;
        return -1;
    }

    // Find video stream index
    int videoStreamIndex = -1;
    for (int i = 0; i < inputFormatContext->nb_streams; i++) {
        if (inputFormatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStreamIndex = i;
            break;
        }
    }
    if (videoStreamIndex == -1) {
        cerr << "Failed to find video stream" << endl;
        return -1;
    }

    // Get video codec parameters
    AVCodecParameters* inputCodecParameters = inputFormatContext->streams[videoStreamIndex]->codecpar;

    // Find video codec
    inputCodec = avcodec_find_decoder(inputCodecParameters->codec_id);
    if (inputCodec == nullptr) {
        cerr << "Failed to find input video codec" << endl;
        return -1;
    }

    // Allocate input codec context
    inputCodecContext = avcodec_alloc_context3(inputCodec);
    if (inputCodecContext == nullptr) {
        cerr << "Failed to allocate input codec context" << endl;
        return -1;
    }

    // Copy codec parameters to input codec context
    if (avcodec_parameters_to_context(inputCodecContext, inputCodecParameters) < 0) {
        cerr << "Failed to copy input codec parameters to context" << endl;
        return -1;
    }

    // Open input codec
    if (avcodec_open2(inputCodecContext, inputCodec, nullptr) < 0) {
        cerr << "Failed to open input codec" << endl;
        return -1;
    }

    // Allocate input frame
    inputFrame = av_frame_alloc();
    if (inputFrame == nullptr) {
        cerr << "Failed to allocate input frame" << endl;
        return -1;
    }

    // Open output file
    if (avformat_alloc_output_context2(&outputFormatContext, nullptr, nullptr, outputFilePath) < 0) {
        cerr << "Failed to allocate output format context" << endl;
        return -1;
    }

    // Find output video codec
    outputCodec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (outputCodec == nullptr) {
        cerr << "Failed to find output video codec" << endl;
        return -1;
    }

    // Allocate output codec context
    outputCodecContext = avcodec_alloc_context3(outputCodec);
    if (outputCodecContext == nullptr) {
        cerr << "Failed to allocate output codec context" << endl;
        return -1;
    }

    // Set output codec parameters
    outputCodecContext->bit_rate = inputCodecContext->bit_rate;
    outputCodecContext->width = inputCodecContext->width;
    outputCodecContext->height = inputCodecContext->height;
    outputCodecContext->time_base = inputCodecContext->time_base;
    outputCodecContext->framerate = inputCodecContext->framerate;
    outputCodecContext->gop_size = inputCodecContext->gop_size;
    outputCodecContext->max_b_frames = inputCodecContext->max_b_frames;
    outputCodecContext->pix_fmt = AV_PIX_FMT_YUV420P;

    // Open output codec
    if (avcodec_open2(outputCodecContext, outputCodec, nullptr) < 0) {
        cerr << "Failed to open output codec" << endl;
        return -1;
    }

    // Allocate output frame
    outputFrame = av_frame_alloc();
    if (outputFrame == nullptr) {
        cerr << "Failed to allocate output frame" << endl;
        return -1;
    }
    outputFrame->format = outputCodecContext->pix_fmt;
    outputFrame->width = outputCodecContext->width;
    outputFrame->height = outputCodecContext->height;
    if (av_frame_get_buffer(outputFrame, 0) < 0) {
        cerr << "Failed to allocate output frame buffer" << endl;
        return -1;
    }

    // Write output file header
    if (avformat_write_header(outputFormatContext, nullptr) < 0) {
        cerr << "Failed to write output file header" << endl;
        return -1;
    }

    // Read input file frames
    while (av_read_frame(inputFormatContext, &inputPacket) == 0) {
        if (inputPacket.stream_index == videoStreamIndex) {
            // Decode input packet
            if (avcodec_send_packet(inputCodecContext, &inputPacket) < 0) {
                cerr << "Failed to send input packet for decoding" << endl;
                return -1;
            }
            while (avcodec_receive_frame(inputCodecContext, inputFrame) == 0) {
                // Convert input frame to output frame
                if (sws_scale(
                    sws_getContext(inputCodecContext->width, inputCodecContext->height, inputCodecContext->pix_fmt,
                        outputCodecContext->width, outputCodecContext->height, outputCodecContext->pix_fmt,
                        SWS_BILINEAR, nullptr, nullptr, nullptr),
                    inputFrame->data, inputFrame->linesize, 0, inputCodecContext->height,
                    outputFrame->data, outputFrame->linesize) <= 0) {
                    cerr << "Failed to convert input frame to output frame" << endl;
                    return -1;
                }

                // Encode output frame
                if (avcodec_send_frame(outputCodecContext, outputFrame) < 0) {
                    cerr << "Failed to send output frame for encoding" << endl;
                    return -1;
                }
                while (avcodec_receive_packet(outputCodecContext, &outputPacket) == 0) {
                    // Write output packet to file
                    if (av_write_frame(outputFormatContext, &outputPacket) < 0) {
                        cerr << "Failed to write output packet to file" << endl;
                        return -1;
                    }
                    av_packet_unref(&outputPacket);
                }
            }
        }
        av_packet_unref(&inputPacket);
    }

    // Flush output codec
    if (avcodec_send_frame(outputCodecContext, nullptr) < 0) {
        cerr << "Failed to send NULL frame for flushing output codec" << endl;
        return -1;
    }
    while (avcodec_receive_packet(outputCodecContext, &outputPacket) == 0) {
        // Write output packet to file
        if (av_write_frame(outputFormatContext, &outputPacket) < 0) {
            cerr << "Failed to write output packet to file" << endl;
            return -1;
        }
        av_packet_unref(&outputPacket);
    }

    // Write output file trailer
    if (av_write_trailer(outputFormatContext) < 0) {
        cerr << "Failed to write output file trailer" << endl;
        return -1;
    }

    // Clean up
    av_frame_free(&inputFrame);
    avcodec_free_context(&inputCodecContext);
    avformat_close_input(&inputFormatContext);
    av_frame_free(&outputFrame);
    avcodec_free_context(&outputCodecContext);
    avformat_free_context(outputFormatContext);

    return 0;
}

此示例假设输入文件为H.264编码，输出文件为H.264编码。如果输入文件为其他编码格式，则可能需要更改示例中的某些参数。此外，使用FFmpeg时需要包含相应的库文件和头文件。