ffmepg dav转mp4 cpp示例

以下是一个简单的使用FFmpeg将dav格式转换为mp4格式的CPP示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

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

int main(int argc, char *argv[]) {
    AVFormatContext *input_ctx = NULL, *output_ctx = NULL;
    AVCodecContext *decoder_ctx = NULL, *encoder_ctx = NULL;
    AVCodec *decoder = NULL, *encoder = NULL;
    AVPacket pkt;
    AVFrame *frame = NULL, *encoder_frame = NULL;
    int stream_index;
    int ret = 0, got_frame = 0;

    if (argc != 3) {
        fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
        exit(1);
    }

    av_register_all();
    avcodec_register_all();
    avformat_network_init();

    // 打开输入文件
    if ((ret = avformat_open_input(&input_ctx, argv[1], NULL, NULL)) < 0) {
        fprintf(stderr, "Could not open input file '%s'", argv[1]);
        goto end;
    }

    // 查找流信息
    if ((ret = avformat_find_stream_info(input_ctx, NULL)) < 0) {
        fprintf(stderr, "Could not find stream information");
        goto end;
    }

    // 找到视频流
    ret = av_find_best_stream(input_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &decoder, 0);
    if (ret < 0) {
        fprintf(stderr, "Could not find video stream in input file '%s'", argv[1]);
        goto end;
    }
    stream_index = ret;

    // 分配解码器上下文
    decoder_ctx = avcodec_alloc_context3(decoder);
    if (!decoder_ctx) {
        fprintf(stderr, "Failed to allocate decoder context");
        goto end;
    }

    // 复制解码器参数
    if ((ret = avcodec_parameters_to_context(decoder_ctx, input_ctx->streams[stream_index]->codecpar)) < 0) {
        fprintf(stderr, "Failed to copy decoder parameters to context");
        goto end;
    }

    // 打开解码器
    if ((ret = avcodec_open2(decoder_ctx, decoder, NULL)) < 0) {
        fprintf(stderr, "Failed to open decoder");
        goto end;
    }

    // 打开输出文件
    if ((ret = avformat_alloc_output_context2(&output_ctx, NULL, NULL, argv[2])) < 0) {
        fprintf(stderr, "Could not create output context");
        goto end;
    }

    // 找到编码器
    encoder = avcodec_find_encoder_by_name("libx264");
    if (!encoder) {
        fprintf(stderr, "Could not find encoder");
        goto end;
    }

    // 创建输出流
    AVStream *output_stream = avformat_new_stream(output_ctx, encoder);
    if (!output_stream) {
        fprintf(stderr, "Failed to create output stream");
        goto end;
    }

    // 分配编码器上下文
    encoder_ctx = avcodec_alloc_context3(encoder);
    if (!encoder_ctx) {
        fprintf(stderr, "Failed to allocate encoder context");
        goto end;
    }

    // 复制编码器参数
    encoder_ctx->codec_id = encoder->id;
    encoder_ctx->bit_rate = decoder_ctx->bit_rate;
    encoder_ctx->width = decoder_ctx->width;
    encoder_ctx->height = decoder_ctx->height;
    encoder_ctx->time_base = decoder_ctx->time_base;
    encoder_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    if ((output_ctx->oformat->flags & AVFMT_GLOBALHEADER) != 0) {
        encoder_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }

    // 打开编码器
    if ((ret = avcodec_open2(encoder_ctx, encoder, NULL)) < 0) {
        fprintf(stderr, "Failed to open encoder");
        goto end;
    }

    // 初始化输出文件
    if (!(output_ctx->oformat->flags & AVFMT_NOFILE)) {
        if ((ret = avio_open(&output_ctx->pb, argv[2], AVIO_FLAG_WRITE)) < 0) {
            fprintf(stderr, "Could not open output file '%s'", argv[2]);
            goto end;
        }
    }

    // 写文件头
    if ((ret = avformat_write_header(output_ctx, NULL)) < 0) {
        fprintf(stderr, "Error occurred when opening output file");
        goto end;
    }

    // 分配解码帧内存
    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Failed to allocate frame");
        goto end;
    }

    // 分配编码帧内存
    encoder_frame = av_frame_alloc();
    if (!encoder_frame) {
        fprintf(stderr, "Failed to allocate encoder frame");
        goto end;
    }

    // 循环读取帧
    while (av_read_frame(input_ctx, &pkt) >= 0) {
        // 判断是否为视频流
        if (pkt.stream_index == stream_index) {
            // 发送数据包到解码器
            ret = avcodec_send_packet(decoder_ctx, &pkt);
            if (ret < 0) {
                fprintf(stderr, "Error sending a packet for decoding");
                goto end;
            }

            // 循环解码帧
            while (ret >= 0) {
                ret = avcodec_receive_frame(decoder_ctx, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                } else if (ret < 0) {
                    fprintf(stderr, "Error during decoding");
                    goto end;
                }

                // 将解码后的帧转换为YUV420P格式
                SwsContext *sws_ctx = sws_getContext(
                    decoder_ctx->width, decoder_ctx->height, decoder_ctx->pix_fmt,
                    encoder_ctx->width, encoder_ctx->height, encoder_ctx->pix_fmt,
                    SWS_BILINEAR, NULL, NULL, NULL);
                if (!sws_ctx) {
                    fprintf(stderr, "Failed to initialize sws context");
                    goto end;
                }
                sws_scale(sws_ctx, frame->data, frame->linesize, 0, decoder_ctx->height, encoder_frame->data, encoder_frame->linesize);
                sws_freeContext(sws_ctx);

                // 编码帧
                ret = avcodec_send_frame(encoder_ctx, encoder_frame);
                if (ret < 0) {
                    fprintf(stderr, "Error sending a frame for encoding");
                    goto end;
                }

                while (ret >= 0) {
                    ret = avcodec_receive_packet(encoder_ctx, &pkt);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                        break;
                    } else if (ret < 0) {
                        fprintf(stderr, "Error during encoding");
                        goto end;
                    }

                    // 更新时间戳
                    av_packet_rescale_ts(&pkt, decoder_ctx->time_base, output_stream->time_base);
                    pkt.stream_index = output_stream->index;

                    // 写入输出文件
                    ret = av_interleaved_write_frame(output_ctx, &pkt);
                    if (ret < 0) {
                        fprintf(stderr, "Error writing packet to output file");
                        goto end;
                    }
                }
            }
        }

        // 释放数据包
        av_packet_unref(&pkt);
    }

    // 写文件尾
    av_write_trailer(output_ctx);

end:
    if (decoder_ctx) {
        avcodec_free_context(&decoder_ctx);
    }
    if (encoder_ctx) {
        avcodec_free_context(&encoder_ctx);
    }
    if (input_ctx) {
        avformat_close_input(&input_ctx);
    }
    if (output_ctx) {
        if (!(output_ctx->oformat->flags & AVFMT_NOFILE)) {
            avio_closep(&output_ctx->pb);
        }
        avformat_free_context(output_ctx);
    }
    if (frame) {
        av_frame_free(&frame);
    }
    if (encoder_frame) {
        av_frame_free(&encoder_frame);
    }
    return ret < 0;
}

注意：在使用该示例代码之前，需要先安装FFmpeg库，并在编译时链接该库。