FFmpeg:从mp4读取配置文件级别信息

// 定义一些变量

const char *input_file = "input.mp4";

const char *output_file = "output.png";

AVFormatContext *format_ctx = NULL;

AVCodecContext *codec_ctx = NULL;

AVCodec *codec = NULL;

AVPacket pkt;

AVFrame *frame = NULL;

AVFrame *rgb_frame = NULL;

struct SwsContext *sws_ctx = NULL;

int video_stream_index = -1;

int frame_count = 0;

int ret = 0;

// 初始化 FFmpeg

av_register_all();

// 打开输入文件

if (avformat_open_input(&format_ctx, input_file, NULL, NULL) != 0) {

    fprintf(stderr, "Could not open file %s\n", input_file);

    ret = 1;

    goto end;

}

// 获取流信息

if (avformat_find_stream_info(format_ctx, NULL) < 0) {

    fprintf(stderr, "Could not find stream information\n");

    ret = 1;

    goto end;

}

// 查找视频流

video_stream_index = av_find_best_stream(format_ctx, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);

if (video_stream_index < 0) {

    fprintf(stderr, "Could not find video stream in file %s\n", input_file);

    ret = 1;

    goto end;

}

// 获取编解码器

codec = avcodec_find_decoder(format_ctx->streams[video_stream_index]->codecpar->codec_id);

if (codec == NULL) {

    fprintf(stderr, "Unsupported codec\n");

    ret = 1;

    goto end;

}

// 创建解码器上下文

codec_ctx = avcodec_alloc_context3(codec);

if (!codec_ctx) {

    fprintf(stderr, "Could not allocate video codec context\n");

    ret = 1;

    goto end;

}

// 配置解码器上下文

if (avcodec_open2(codec_ctx, codec, NULL) < 0) {

    fprintf(stderr, "Could not open codec\n");

    ret = 1;

    goto end;

}

// 读取数据包

pkt.data = NULL;

pkt.size = 0;

while (av_read_frame(format_ctx, &pkt) >= 0) {

    if (pkt.stream_index == video_stream_index) {

        // 解码数据

        ret = avcodec_send_packet(codec_ctx, &pkt);

        if (ret < 0) {

            fprintf(stderr, "Error sending a packet for decoding\n");

            ret = 1;

            goto end;

        }

        // 获取解码后的数据

        ret = avcodec_receive_frame(codec_ctx, frame);

        if (ret < 0) {

            fprintf(stderr, "Error receiving a frame from the codec\n");

            ret =