ffmpeg dav转mp4 cpp示例

以下是使用 FFmpeg C++ API 将 DAV 文件转换为 MP4 文件的示例代码：

#include <iostream>
#include <string>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <fstream>

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

using namespace std;

int main(int argc, char* argv[]) {
    if (argc < 3) {
        cout << "Usage: " << argv[0] << " input.dav output.mp4" << endl;
        return 1;
    }

    char* input_file = argv[1];
    char* output_file = argv[2];

    av_register_all();
    avcodec_register_all();

    AVFormatContext* input_format_ctx = NULL;
    AVFormatContext* output_format_ctx = NULL;

    if (avformat_open_input(&input_format_ctx, input_file, NULL, NULL) != 0) {
        cout << "Error: could not open input file." << endl;
        return 1;
    }

    if (avformat_find_stream_info(input_format_ctx, NULL) < 0) {
        cout << "Error: could not find stream information." << endl;
        return 1;
    }

    if (avformat_alloc_output_context2(&output_format_ctx, NULL, NULL, output_file) < 0) {
        cout << "Error: could not allocate output context." << endl;
        return 1;
    }

    AVCodec* codec = NULL;
    AVCodecParameters* codec_params = NULL;
    int video_stream_index = -1;

    for (int i = 0; i < input_format_ctx->nb_streams; i++) {
        AVStream* stream = input_format_ctx->streams[i];
        codec_params = stream->codecpar;
        codec = avcodec_find_decoder(codec_params->codec_id);

        if (codec == NULL) {
            continue;
        }

        if (codec_params->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_stream_index = i;
            break;
        }
    }

    if (video_stream_index == -1) {
        cout << "Error: could not find video stream." << endl;
        return 1;
    }

    AVStream* input_stream = input_format_ctx->streams[video_stream_index];
    AVStream* output_stream = avformat_new_stream(output_format_ctx, codec);

    if (output_stream == NULL) {
        cout << "Error: could not create output stream." << endl;
        return 1;
    }

    if (avcodec_parameters_copy(output_stream->codecpar, codec_params) < 0) {
        cout << "Error: could not copy codec parameters." << endl;
        return 1;
    }

    AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);
    if (codec_ctx == NULL) {
        cout << "Error: could not allocate codec context." << endl;
        return 1;
    }

    if (avcodec_parameters_to_context(codec_ctx, codec_params) < 0) {
        cout << "Error: could not convert codec parameters to codec context." << endl;
        return 1;
    }

    if (avcodec_open2(codec_ctx, codec, NULL) < 0) {
        cout << "Error: could not open codec." << endl;
        return 1;
    }

    av_dump_format(input_format_ctx, 0, input_file, 0);
    av_dump_format(output_format_ctx, 0, output_file, 1);

    AVPacket packet;
    int frame_cnt = 0;

    if (avformat_write_header(output_format_ctx, NULL) < 0) {
        cout << "Error: could not write output file header." << endl;
        return 1;
    }

    while (av_read_frame(input_format_ctx, &packet) >= 0) {
        if (packet.stream_index != video_stream_index) {
            av_packet_unref(&packet);
            continue;
        }

        AVFrame* frame = av_frame_alloc();
        int ret = avcodec_send_packet(codec_ctx, &packet);

        if (ret < 0) {
            av_packet_unref(&packet);
            av_frame_free(&frame);
            continue;
        }

        while (ret >= 0) {
            ret = avcodec_receive_frame(codec_ctx, frame);

            if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                av_frame_free(&frame);
                break;
            }

            sws_scale(sws_getContext(codec_ctx->width, codec_ctx->height, codec_ctx->pix_fmt, codec_ctx->width, codec_ctx->height, AV_PIX_FMT_YUV420P, 0, NULL, NULL, NULL), frame->data, frame->linesize, 0, codec_ctx->height, frame->data, frame->linesize);

            frame_cnt++;

            frame->pts = frame_cnt * input_stream->time_base.den / av_rescale_q(1, AV_TIME_BASE_Q, input_stream->time_base);
            frame->pkt_dts = frame->pts;

            av_packet_unref(&packet);
            av_init_packet(&packet);

            if (avcodec_send_frame(codec_ctx, frame) < 0) {
                av_frame_free(&frame);
                continue;
            }

            while (1) {
                ret = avcodec_receive_packet(codec_ctx, &packet);

                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
                    break;
                }

                av_packet_rescale_ts(&packet, codec_ctx->time_base, output_stream->time_base);
                packet.stream_index = output_stream->index;

                if (av_write_frame(output_format_ctx, &packet) < 0) {
                    av_packet_unref(&packet);
                    continue;
                }

                av_packet_unref(&packet);
            }

            av_frame_free(&frame);
        }
    }

    if (av_write_trailer(output_format_ctx) < 0) {
        cout << "Error: could not write output file trailer." << endl;
        return 1;
    }

    avformat_close_input(&input_format_ctx);
    avformat_free_context(input_format_ctx);

    if (!(output_format_ctx->flags & AVFMT_NOFILE)) {
        avio_closep(&output_format_ctx->pb);
    }

    avformat_free_context(output_format_ctx);

    return 0;
}

其中，使用 `avformat_open_input` 打开输入文件， `avformat_find_stream_info` 查找流信息， `avformat_alloc_output_context2` 分配输出上下文， `avcodec_find_decoder` 查找解码器， `avcodec_open2` 打开解码器， `av_read_frame` 读取帧， `avcodec_send_packet` 发送数据包， `avcodec_receive_frame` 接收帧， `sws_scale` 进行图像缩放， `avcodec_send_frame` 发送帧， `avcodec_receive_packet` 接收数据包， `av_write_frame` 写入数据帧， `av_write_trailer` 写入尾帧， `avformat_close_input` 关闭输入文件， `avformat_free_context` 释放上下文等函数完成转换任务。

使用时，需要将 DAV 文件和 MP4 文件的路径传入程序作为参数，例如：

./dav2mp4 input.dav output.mp4