ffmepg cpp dav转mp4

使用FFmpeg库可以将DAV文件转换为MP4格式。以下是C++代码示例：

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

int main()
{
    const char* input_filename = "input.dav";
    const char* output_filename = "output.mp4";
    AVFormatContext* input_format_context = nullptr;
    AVFormatContext* output_format_context = nullptr;
    AVCodec* codec = nullptr;
    AVCodecContext* codec_context = nullptr;
    AVStream* stream = nullptr;
    AVPacket packet;
    AVFrame* frame = nullptr;
    SwsContext* sws_context = nullptr;
    uint8_t* buffer = nullptr;
    int video_stream_index = -1;
    int ret = 0;

    // Open input file
    ret = avformat_open_input(&input_format_context, input_filename, nullptr, nullptr);
    if (ret < 0)
    {
        printf("Error opening input file\n");
        return -1;
    }

    // Get stream information
    ret = avformat_find_stream_info(input_format_context, nullptr);
    if (ret < 0)
    {
        printf("Error getting stream information\n");
        return -1;
    }

    // Find video stream
    for (unsigned int i = 0; i < input_format_context->nb_streams; i++)
    {
        if (input_format_context->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            video_stream_index = i;
            break;
        }
    }

    if (video_stream_index == -1)
    {
        printf("Error finding video stream\n");
        return -1;
    }

    // Open codec
    codec = avcodec_find_decoder(input_format_context->streams[video_stream_index]->codecpar->codec_id);
    if (!codec)
    {
        printf("Error finding decoder\n");
        return -1;
    }

    codec_context = avcodec_alloc_context3(codec);
    if (!codec_context)
    {
        printf("Error allocating codec context\n");
        return -1;
    }

    ret = avcodec_parameters_to_context(codec_context, input_format_context->streams[video_stream_index]->codecpar);
    if (ret < 0)
    {
        printf("Error setting codec parameters\n");
        return -1;
    }

    ret = avcodec_open2(codec_context, codec, nullptr);
    if (ret < 0)
    {
        printf("Error opening codec\n");
        return -1;
    }

    // Open output file
    avformat_alloc_output_context2(&output_format_context, nullptr, nullptr, output_filename);
    if (!output_format_context)
    {
        printf("Error allocating output context\n");
        return -1;
    }

    codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    if (!codec)
    {
        printf("Error finding encoder\n");
        return -1;
    }

    stream = avformat_new_stream(output_format_context, codec);
    if (!stream)
    {
        printf("Error creating new stream\n");
        return -1;
    }

    codec_context = avcodec_alloc_context3(codec);
    if (!codec_context)
    {
        printf("Error allocating codec context\n");
        return -1;
    }

    codec_context->codec_id = codec->id;
    codec_context->codec_type = AVMEDIA_TYPE_VIDEO;
    codec_context->width = input_format_context->streams[video_stream_index]->codecpar->width;
    codec_context->height = input_format_context->streams[video_stream_index]->codecpar->height;
    codec_context->time_base = input_format_context->streams[video_stream_index]->time_base;
    codec_context->pix_fmt = AV_PIX_FMT_YUV420P;

    ret = avcodec_parameters_from_context(stream->codecpar, codec_context);
    if (ret < 0)
    {
        printf("Error setting codec parameters\n");
        return -1;
    }

    ret = avcodec_open2(codec_context, codec, nullptr);
    if (ret < 0)
    {
        printf("Error opening codec\n");
        return -1;
    }

    ret = avio_open(&output_format_context->pb, output_filename, AVIO_FLAG_WRITE);
    if (ret < 0)
    {
        printf("Error opening output file\n");
        return -1;
    }

    ret = avformat_write_header(output_format_context, nullptr);
    if (ret < 0)
    {
        printf("Error writing header\n");
        return -1;
    }

    // Allocate frame and buffer
    frame = av_frame_alloc();
    if (!frame)
    {
        printf("Error allocating frame\n");
        return -1;
    }

    int buffer_size = av_image_get_buffer_size(codec_context->pix_fmt, codec_context->width, codec_context->height, 1);
    buffer = (uint8_t*)av_malloc(buffer_size * sizeof(uint8_t));

    av_image_fill_arrays(frame->data, frame->linesize, buffer, codec_context->pix_fmt, codec_context->width, codec_context->height, 1);

    sws_context = sws_getContext(input_format_context->streams[video_stream_index]->codecpar->width, input_format_context->streams[video_stream_index]->codecpar->height, input_format_context->streams[video_stream_index]->codecpar->format, codec_context->width, codec_context->height, codec_context->pix_fmt, SWS_BICUBIC, nullptr, nullptr, nullptr);

    // Read frames and write to output file
    while (av_read_frame(input_format_context, &packet) >= 0)
    {
        if (packet.stream_index == video_stream_index)
        {
            ret = avcodec_send_packet(codec_context, &packet);
            if (ret < 0)
            {
                printf("Error sending packet to decoder\n");
                return -1;
            }

            while (ret >= 0)
            {
                ret = avcodec_receive_frame(codec_context, frame);
                if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                    break;
                else if (ret < 0)
                {
                    printf("Error receiving frame from decoder\n");
                    return -1;
                }

                sws_scale(sws_context, frame->data, frame->linesize, 0, input_format_context->streams[video_stream_index]->codecpar->height, frame->data, frame->linesize);

                frame->pts = av_rescale_q(frame->pts, input_format_context->streams[video_stream_index]->time_base, stream->time_base);
                frame->pkt_dts = av_rescale_q(frame->pkt_dts, input_format_context->streams[video_stream_index]->time_base, stream->time_base);
                frame->pkt_duration = av_rescale_q(frame->pkt_duration, input_format_context->streams[video_stream_index]->time_base, stream->time_base);
                frame->pkt_pos = -1;

                ret = avcodec_send_frame(codec_context, frame);
                if (ret < 0)
                {
                    printf("Error sending frame to encoder\n");
                    return -1;
                }

                while (ret >= 0)
                {
                    ret = avcodec_receive_packet(codec_context, &packet);
                    if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
                        break;
                    else if (ret < 0)
                    {
                        printf("Error receiving packet from encoder\n");
                        return -1;
                    }

                    packet.stream_index = stream->index;
                    packet.pts = av_rescale_q(packet.pts, codec_context->time_base, stream->time_base);
                    packet.dts = av_rescale_q(packet.dts, codec_context->time_base, stream->time_base);
                    packet.duration = av_rescale_q(packet.duration, codec_context->time_base, stream->time_base);
                    packet.pos = -1;

                    ret = av_interleaved_write_frame(output_format_context, &packet);
                    if (ret < 0)
                    {
                        printf("Error writing packet\n");
                        return -1;
                    }

                    av_packet_unref(&packet);
                }
            }
        }

        av_packet_unref(&packet);
    }

    // Flush encoder
    ret = avcodec_send_frame(codec_context, nullptr);
    if (ret < 0)
    {
        printf("Error flushing encoder\n");
        return -1;
    }

    while (ret >= 0)
    {
        ret = avcodec_receive_packet(codec_context, &packet);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            break;
        else if (ret < 0)
        {
            printf("Error receiving packet from encoder\n");
            return -1;
        }

        packet.stream_index = stream->index;
        packet.pts = av_rescale_q(packet.pts, codec_context->time_base, stream->time_base);
        packet.dts = av_rescale_q(packet.dts, codec_context->time_base, stream->time_base);
        packet.duration = av_rescale_q(packet.duration, codec_context->time_base, stream->time_base);
        packet.pos = -1;

        ret = av_interleaved_write_frame(output_format_context, &packet);
        if (ret < 0)
        {
            printf("Error writing packet\n");
            return -1;
        }

        av_packet_unref(&packet);
    }

    av_write_trailer(output_format_context);

    // Free memory
    if (input_format_context)
        avformat_close_input(&input_format_context);
    if (output_format_context)
    {
        if (output_format_context->pb)
            avio_closep(&output_format_context->pb);
        avformat_free_context(output_format_context);
    }
    if (codec_context)
        avcodec_free_context(&codec_context);
    if (frame)
        av_frame_free(&frame);
    if (buffer)
        av_free(buffer);
    if (sws_context)
        sws_freeContext(sws_context);

    return 0;
}

上述代码使用了FFmpeg库中的许多功能，例如打开文件、解码视频、编码视频、写入文件等。如果您不熟悉FFmpeg，建议先了解一些基本的概念和用法。