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我编写了一段 C++ 代码，可以捕获网络摄像头视频帧，对其进行解码，将它们转换为 YUV420P，对其进行编码，然后将它们写入文件。如果我使用 mpeg2 编解码器并写入 .mpg 文件，则一切正常。但是，如果我使用 flv，那么产生的输出只是一个绿屏。我不确定是否需要为编码 flv 视频设置不同的编码器设置？这是我的代码（相关部分）：

编码器设置：

    c->codec_id = codec_id;
    c->bit_rate = 400000;
    // Resolution must be a multiple of two.
    c->width    = 352;
    c->height   = 288;
    c->time_base.den = STREAM_FRAME_RATE;
    c->time_base.num = 1;
    //emit one intra frame every twelve frames at most
    c->gop_size      = 12;
    c->pix_fmt       = STREAM_PIX_FMT;

写框架：

    int ret;
uint8_t *buffer = NULL;
static struct SwsContext *sws_ctx;

//Setup the codec context, and set its width and height to be equal to the input video width and height
AVCodecContext *c = st->codec;
c->width = pCodecCtx->width;
c->height = pCodecCtx->height;

av_init_packet(&packet);
frameYUV = avcodec_alloc_frame();

//Determine how big the buffer will need to be to store the captured frame
numBytes = avpicture_get_size(STREAM_PIX_FMT,pCodecCtx->width,pCodecCtx->height);

//Allocate the needed buffer size
buffer = new uint8_t[numBytes];
sws_ctx = sws_getContext(pCodecCtx->width,pCodecCtx->height,pCodecCtx->pix_fmt,
                        pCodecCtx->width,pCodecCtx->height,
                        STREAM_PIX_FMT,SWS_BILINEAR,NULL,NULL,NULL);

//Fill the output frame
avpicture_fill((AVPicture *)frameYUV,buffer,STREAM_PIX_FMT,pCodecCtx->width,pCodecCtx->height);

//Read a video frame in
av_read_frame(pFormatCtx,&packet);

//Decode the contents of packet into pFrame
avcodec_decode_video2(pCodecCtx,pFrame,&frameFinished,&packet);

//Scale pFrame into frameYUV, and convert to PIXFMTYUV420P
sws_scale
(
    sws_ctx,
    (uint8_t const * const *)pFrame->data,
    pFrame->linesize,
    0,
    pCodecCtx->height,
    frameYUV->data,
    frameYUV->linesize
);
av_init_packet(&samsPacket);

//Encode frameYUV
avcodec_encode_video2(c, &samsPacket, frameYUV, &gotSamsPacket);

AVPacket pkt = { 0 };
int got_packet;
av_init_packet(&pkt);
// encode the image
ret = avcodec_encode_video2(c, &pkt, frame, &got_packet);
if (ret < 0){
    debugLogStreamSave->debug("Error encoding video frame");
    exit(1);
}
if (!ret && got_packet && pkt.size){
    pkt.stream_index = st->index;

    // Write the compressed frame to our output
    ret = av_interleaved_write_frame(oc, &pkt);
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