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• libav : How to clear real-time buffer ?

  29 novembre 2018, par user67

  Here’s the c++ code that I’m using to access my webcam.

  int Camera::Init(char* file_name,
  
                  char* device_name,
  
                  char* format,
  
                  char* resolution,
  
                  char* frame_rate,
  
                  char* pixel_format)
  
  {
  
      av_log(NULL, AV_LOG_INFO, "---INIT STARTED\n");
  
      avdevice_register_all();
  
      av_register_all();
  
  
  
      AVDictionary* properties_collection = NULL;
  
      av_dict_set(&properties_collection, "f", format, NULL);
  
      av_dict_set(&properties_collection, "video_size", resolution, NULL);
  
      av_dict_set(&properties_collection, "framerate", frame_rate, NULL);
  
      av_dict_set(&properties_collection, "pix_fmt", pixel_format, NULL);
  
      AVInputFormat *input_format = av_find_input_format("dshow");
  
      char command_line[256];
  
      sprintf(command_line, "video=%s", device_name);
  
      AVFormatContext *input_context = avformat_alloc_context();
  
      //input_context->flags |= AVFMT_FLAG_NOBUFFER;      //DOESN'T HELP
  
      //input_context->max_picture_buffer = 0;            //ERR
  
  
  
      int err_code = 0;
  
      err_code = avformat_open_input(&input_context,
  
                                      command_line,
  
                                      input_format,
  
                                      &properties_collection);
  
      int i = 0;
  
      while (i++ < 30)
  
      {
  
          Sleep(1000);
  
          //avformat_flush(input_context); //DOESN'T HELP
  
          //av_free(input_context); //ERR
  
      }
  
      system("pause");
  
      return 0;
  
  }

  Right after "avformat_open_input()" it starts reading frames to some internal buffer without me even calling "av_read_frame()".
  After about 10 seconds it start’s giving me error messages :

  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (62% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!
  
  ...
  
  ...
  
  ...
  
  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (100% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!

  How to clear this buffer or avoid using it ?

  Thanks in advance.

  P.S.Please pardon my english.

  P.P.S.Have a good day.

• FFMPEG API : How to clear real-time buffer ?

  29 novembre 2018, par user67

  Here’s the c++ code that I’m using to access my webcam.

  int Camera::Init(char* file_name,
  
                  char* device_name,
  
                  char* format,
  
                  char* resolution,
  
                  char* frame_rate,
  
                  char* pixel_format)
  
  {
  
      av_log(NULL, AV_LOG_INFO, "---INIT STARTED\n");
  
      avdevice_register_all();
  
      av_register_all();
  
  
  
      AVDictionary* properties_collection = NULL;
  
      av_dict_set(&properties_collection, "f", format, NULL);
  
      av_dict_set(&properties_collection, "video_size", resolution, NULL);
  
      av_dict_set(&properties_collection, "framerate", frame_rate, NULL);
  
      av_dict_set(&properties_collection, "pix_fmt", pixel_format, NULL);
  
      AVInputFormat *input_format = av_find_input_format("dshow");
  
      char command_line[256];
  
      sprintf(command_line, "video=%s", device_name);
  
      AVFormatContext *input_context = avformat_alloc_context();
  
      //input_context->flags |= AVFMT_FLAG_NOBUFFER;      //DOESN'T HELP
  
      //input_context->max_picture_buffer = 0;            //ERR
  
  
  
      int err_code = 0;
  
      err_code = avformat_open_input(&input_context,
  
                                      command_line,
  
                                      input_format,
  
                                      &properties_collection);
  
      int i = 0;
  
      while (i++ < 30)
  
      {
  
          Sleep(1000);
  
          //avformat_flush(input_context); //DOESN'T HELP
  
          //av_free(input_context); //ERR
  
      }
  
      system("pause");
  
      return 0;
  
  }

  Right after "avformat_open_input()" it starts reading frames to some internal buffer without me even calling "av_read_frame()".
  After about 10 seconds it start’s giving me error messages :

  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (62% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!
  
  ...
  
  ...
  
  ...
  
  [dshow @ 0014ed40] real-time buffer [VirtualBox Webcam - FULL HD 1080P Webcam] [video input] 
  
  too full or near too full (100% of size: 3041280 [rtbufsize parameter])! 
  
  frame dropped!

  How to clear this buffer or avoid using it ?

  Thanks in advance.

  P.S.Please pardon my english.

  P.P.S.Have a good day.

• Incorrect height for U and V channel when creating video from jpgs using ffmpeg

  27 juillet 2022, par Chu Bun

  I use the method in the ffmpeg source sample decode_video.c to decode a series of jpgs into AVFrames. Then use the method in the sample encode_video.c to combine the AVFrames into a video file.

  


  AV_CODEC_ID_MJPEG is used to set up the decoder for the jpgs. The output frames have the format AV_PIX_FMT_YUVJ422P which has (full-width x full-height) Y-channel, and (half-width x full-height) U and V channels. The problem is when I try to encode the frames, ffmpeg seems to expect (half-width x half-height) U and V channels. As a result the colors are stretch in the vertical direction and do not match with the image in the Y-channel.

  


  I could not figure out how to either decode the jpgs into YUV420 (half-width x half-height) frames, or encode frames in YUV422 format. Any pointers ?