Question

我尝试了代码based on this tutorial。这样做是将视频的前5帧以RGB格式写入存储器。我需要将这些RGB帧转换为YUV420P格式，以便我可以将它们传递给YUV420P编码器。我尝试使用sws_scale，但随后生成的帧会丢失颜色信息，并且还会遇到缩放问题。此外，看了各种问题，但没有一个提供有效的解决方案。我是FFmpeg库的新手，并且正在处理各种教程以掌握它。我希望有人能提出一个很好的解决方案。非常感谢您的投入！

以下是代码：

#include <ffmpeg/avcodec.h>
#include <ffmpeg/avformat.h>

#include <stdio.h>

void SaveFrame(AVFrame *pFrame, int width, int height, int iFrame) {
  FILE *pFile;
  char szFilename[32];
  int  y;

  // Open file
  sprintf(szFilename, "frame%d.ppm", iFrame);
  pFile=fopen(szFilename, "wb");
  if(pFile==NULL)
    return;

  // Write header
  fprintf(pFile, "P6\n%d %d\n255\n", width, height);

  // Write pixel data
  for(y=0; y<height; y++)
    fwrite(pFrame->data[0]+y*pFrame->linesize[0], 1, width*3, pFile);

  // Close file
  fclose(pFile);
}

int main(int argc, char *argv[]) {
  AVFormatContext *pFormatCtx;
  int             i, videoStream;
  AVCodecContext  *pCodecCtx;
  AVCodec         *pCodec;
  AVFrame         *pFrame; 
  AVFrame         *pFrameRGB;
  AVPacket        packet;
  int             frameFinished;
  int             numBytes;
  uint8_t         *buffer;

  if(argc < 2) {
    printf("Please provide a movie file\n");
    return -1;
  }
  // Register all formats and codecs
  av_register_all();

  // Open video file
  if(av_open_input_file(&pFormatCtx, argv[1], NULL, 0, NULL)!=0)
    return -1; // Couldn't open file

  // Retrieve stream information
  if(av_find_stream_info(pFormatCtx)<0)
    return -1; // Couldn't find stream information

  // Dump information about file onto standard error
  dump_format(pFormatCtx, 0, argv[1], 0);

  // Find the first video stream
  videoStream=-1;
  for(i=0; i<pFormatCtx->nb_streams; i++)
    if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO) {
      videoStream=i;
      break;
    }
  if(videoStream==-1)
    return -1; // Didn't find a video stream

  // Get a pointer to the codec context for the video stream
  pCodecCtx=pFormatCtx->streams[videoStream]->codec;

  // Find the decoder for the video stream
  pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
  if(pCodec==NULL) {
    fprintf(stderr, "Unsupported codec!\n");
    return -1; // Codec not found
  }
  // Open codec
  if(avcodec_open(pCodecCtx, pCodec)<0)
    return -1; // Could not open codec

  // Allocate video frame
  pFrame=avcodec_alloc_frame();

  // Allocate an AVFrame structure
  pFrameRGB=avcodec_alloc_frame();
  if(pFrameRGB==NULL)
    return -1;

  // Determine required buffer size and allocate buffer
  numBytes=avpicture_get_size(PIX_FMT_RGB24, pCodecCtx->width,
                  pCodecCtx->height);
  buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));

  // Assign appropriate parts of buffer to image planes in pFrameRGB
  // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
  // of AVPicture
  avpicture_fill((AVPicture *)pFrameRGB, buffer, PIX_FMT_RGB24,
         pCodecCtx->width, pCodecCtx->height);

  // Read frames and save first five frames to disk
  i=0;
  while(av_read_frame(pFormatCtx, &packet)>=0) {
    // Is this a packet from the video stream?
    if(packet.stream_index==videoStream) {
      // Decode video frame
      avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, 
               packet.data, packet.size);

      // Did we get a video frame?
      if(frameFinished) {
    // Convert the image from its native format to RGB
    img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24, 
                    (AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width, 
                    pCodecCtx->height);

    // Save the frame to disk
    if(++i<=5)
      SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, 
            i);
      }
    }

    // Free the packet that was allocated by av_read_frame
    av_free_packet(&packet);
  }

  // Free the RGB image
  av_free(buffer);
  av_free(pFrameRGB);

  // Free the YUV frame
  av_free(pFrame);

  // Close the codec
  avcodec_close(pCodecCtx);

  // Close the video file
  av_close_input_file(pFormatCtx);

  return 0;
}

Answer 1

您从其他人的网站复制并粘贴了旧代码，这些代码甚至无法使用最近的libav *进行编译。您询问的是sws_scale，此代码甚至不使用它。所以代码与问题100％无关。最重要的是，你之前已经问过这个问题了，我已经回答了。 ffmpeg: RGB to YUV conversion loses color and scale

使用FFmpeg / C ++将RGB帧转换为YUV420P

1 个答案: