问返回相同颜色的FFMpeg(安卓) av_read_frame或avcodec_decode_video2

EN

while(av_read_frame(gFormatCtx, &packet)>=0)
        {
            // Is this a packet from the video stream?
            if(packet.stream_index==videoStream)
            {
                // Decode video frame
                avcodec_decode_video2(gVideoCodecCtx, pFrame, &frameFinished, &packet);
                // Did we get a video frame?
                if(frameFinished)
                {//and so on... But our problem is already here...

char yuvFileName[100];
sprintf(yuvFileName,"/storage/sdcard0/yuv%d.yuv",index);
FILE* fp = fopen(yuvFileName, "wb");
int y;
// Write pixel data
for(y=0; y<gVideoCodecCtx->height; y++)
{
    fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, gVideoCodecCtx->width, fp);    
}
for(y=0; y<gVideoCodecCtx->height/2; y++)
{
    fwrite(pFrame->data[1]+y*pFrame->linesize[1], 1, gVideoCodecCtx->width/2, fp);
}
for(y=0; y<gVideoCodecCtx->height/2; y++)
{
    fwrite(pFrame->data[2]+y*pFrame->linesize[2], 1, gVideoCodecCtx->width/2, fp);
}
fclose(fp);