ffmpeg提取h264视频帧率的源码

以下是使用FFmpeg提取H.264视频帧率的样例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libavutil/mathematics.h>

int main(int argc, char* argv[])
{
    AVFormatContext *pFormatCtx = NULL;
    int i, videoStream;
    AVCodecContext *pCodecCtxOrig = NULL, *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVFrame *pFrame = NULL;
    AVPacket packet;
    int frameFinished;
    float fps = 0;

    if(argc < 2)
    {
        printf("Usage: %s <video_file>\n", argv[0]);
        return -1;
    }

    av_register_all();

    if(avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0)
    {
        printf("Error: Couldn't open input file!\n");
        return -1;
    }

    if(avformat_find_stream_info(pFormatCtx, NULL) < 0)
    {
        printf("Error: Couldn't find stream information!\n");
        return -1;
    }

    av_dump_format(pFormatCtx, 0, argv[1], 0);

    videoStream = -1;

    for(i = 0; i < pFormatCtx->nb_streams; i++)
    {
        if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            videoStream = i;
            break;
        }
    }

    if(videoStream == -1)
    {
        printf("Error: Couldn't find a video stream!\n");
        return -1;
    }

    pCodecCtxOrig = pFormatCtx->streams[videoStream]->codec;
    pCodec = avcodec_find_decoder(pCodecCtxOrig->codec_id);

    if(pCodec == NULL)
    {
        printf("Error: Unsupported codec!\n");
        return -1;
    }

    pCodecCtx = avcodec_alloc_context3(pCodec);

    if(avcodec_copy_context(pCodecCtx, pCodecCtxOrig) != 0)
    {
        printf("Error: Couldn't copy codec context!\n");
        return -1;
    }

    if(avcodec_open2(pCodecCtx, pCodec, NULL) < 0)
    {
        printf("Error: Couldn't open codec!\n");
        return -1;
    }

    pFrame = av_frame_alloc();

    while(av_read_frame(pFormatCtx, &packet) >= 0)
    {
        if(packet.stream_index == videoStream)
        {
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);

            if(frameFinished)
            {
                fps = av_q2d(pFormatCtx->streams[videoStream]->r_frame_rate);
                break;
            }
        }

        av_free_packet(&packet);
    }

    av_free(pFrame);
    avcodec_close(pCodecCtx);
    avcodec_close(pCodecCtxOrig);
    avformat_close_input(&pFormatCtx);

    printf("FPS: %.2f\n", fps);

    return 0;
}

运行样例代码时，需要将 H.264 视频文件名作为命令行参数传递给程序。程序将会输出视频的帧率。