ffmpeg 视频流解码

以下是使用FFmpeg API实现视频流解码的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/time.h>
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>

#define MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audio

// 视频流解码线程
void *decode_video_thread(void *arg)
{
    AVFormatContext *pFormatCtx = NULL;
    AVCodecContext *pCodecCtx = NULL;
    AVCodec *pCodec = NULL;
    AVFrame *pFrame = NULL;
    AVPacket packet;
    int videoStream = -1;
    int frameFinished = 0;
    struct SwsContext *img_convert_ctx = NULL;

    // 打开视频流
    if (avformat_open_input(&pFormatCtx, "rtsp://xxx.xxx.xxx.xxx:xxxx/xxx", NULL, NULL) != 0) {
        printf("Couldn't open input stream.\n");
        return NULL;
    }

    // 查找视频流信息
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        printf("Couldn't find stream information.\n");
        return NULL;
    }

    // 查找视频流
    for (int i = 0; i < pFormatCtx->nb_streams; i++) {
        if (pFormatCtx->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
            videoStream = i;
            break;
        }
    }

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

    // 获取视频解码器
    pCodec = avcodec_find_decoder(pFormatCtx->streams[videoStream]->codecpar->codec_id);
    if (pCodec == NULL) {
        printf("Codec not found.\n");
        return NULL;
    }

    // 初始化解码器上下文
    pCodecCtx = avcodec_alloc_context3(pCodec);
    if (avcodec_parameters_to_context(pCodecCtx, pFormatCtx->streams[videoStream]->codecpar) < 0) {
        printf("Couldn't copy codec context.\n");
        return NULL;
    }

    // 打开解码器
    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {
        printf("Couldn't open codec.\n");
        return NULL;
    }

    // 分配视频帧内存
    pFrame = av_frame_alloc();
    if (pFrame == NULL) {
        printf("Couldn't allocate video frame.\n");
        return NULL;
    }

    // 初始化图像转换上下文
    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
                                     pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_RGB24,
                                     SWS_BICUBIC, NULL, NULL, NULL);
    if (img_convert_ctx == NULL) {
        printf("Couldn't initialize sws context.\n");
        return NULL;
    }

    // 读取视频流
    while (av_read_frame(pFormatCtx, &packet) >= 0) {
        if (packet.stream_index == videoStream) {
            // 解码视频帧
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
            if (frameFinished) {
                // 转换图像格式
                uint8_t *out_buffer = (uint8_t *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1));
                av_image_fill_arrays(pFrame->data, pFrame->linesize, out_buffer, AV_PIX_FMT_RGB24, pCodecCtx->width, pCodecCtx->height, 1);
                sws_scale(img_convert_ctx, (const uint8_t *const *)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrame->data, pFrame->linesize);

                // 处理图像数据
                // ...

                av_free(out_buffer);
            }
        }
        av_packet_unref(&packet);
    }

    // 释放资源
    sws_freeContext(img_convert_ctx);
    av_frame_free(&pFrame);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return NULL;
}

// 主函数
int main(int argc, char *argv[])
{
    // 初始化FFmpeg库
    av_register_all();
    avformat_network_init();

    // 创建视频流解码线程
    pthread_t tid;
    pthread_create(&tid, NULL, decode_video_thread, NULL);

    // 等待线程结束
    pthread_join(tid, NULL);

    return 0;
}