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• Can I decode this audio format ?

  30 octobre 2013, par Naftuli Tzvi Kay

  I'm writing a Python program which depends on FFMPEG to decode audio into WAV format. I'd like to be able to process as many types of audio, but I need a way to quickly check if I can actually work with the uploaded file or not. I've compiled my own FFMPEG installation here.

  Specifically, I'd like to enforce logic like this in my application :

  if ffmpeg_type(file_path) is not "audio":
  
      raise Exception("Bro, that's not an audio file.")
  
  elif not ffmpeg_can_decode_audio(file_path):
  
      raise Exception("I have no way of working with this.")

  (I realize that it wouldn't be as easy as just calling these methods, I assume I'd need to parse output from a system call.)

  Is there a way that I could use the command-line ffmpeg, ffprobe, etc. to determine if a given file is an audio file and if I can decode it ?

• Capture JPEG frame from avi file using ffmpeg library. How to open captured files ?

  30 novembre 2013, par ios198

  This is the code I found from the ffmpeg tutorial website :

  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include 
  
  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); // szFilenam = frame4.ppm
  
    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; ydata[0]+y*pFrame->linesize[0], 1, width*3, pFile);
  
  
  
    // Close file
  
    fclose(pFile);
  
  }
  
  
  
  int main(int argc, char **argv[])
  
  {
  
      AVFormatContext *pFormatCtx = NULL;
  
      int             i, videoStream;
  
      AVCodecContext  *pCodecCtx = NULL;
  
      AVCodec         *pCodec = NULL;
  
      AVFrame         *pFrame = NULL; 
  
      AVFrame         *pFrameRGB = NULL;
  
      AVPacket        packet;
  
      int             frameFinished;
  
      int             numBytes;
  
      uint8_t         *buffer = NULL;
  
  
  
      AVDictionary    *optionsDict = NULL;
  
      struct SwsContext      *sws_ctx = NULL;
  
  
  
  
  
      // Register all formats and codecs
  
      av_register_all();
  
  
  
      // Open video file
  
      if(avformat_open_input(&amp;pFormatCtx, "/root/dhquan/AVI/turning_pages.avi", NULL, NULL)!=0)
  
          return -1; // couldn&#39;t open file
  
  
  
      // Retrieve stream information
  
      if(avformat_find_stream_info(pFormatCtx,NULL)&lt;0)
  
          return -1; // couldn&#39;t find stream information
  
                     // This function populates pFormatCtx->streams with the proper 
  
  
  
      // dump information about file onto standard error
  
      av_dump_format(pFormatCtx, 0, "/root/dhquan/AVI/turning_pages.avi", 0);
  
  
  
      // Find the first video stream
  
      videoStream = -1;
  
      for(i=0;inb_streams;i++)
  
          if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
  
              videoStream=i;
  
              break;
  
          }
  
          if(videoStream==-1)
  
              return -1; // didn&#39;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;
  
          }
  
  
  
      // Open Codec
  
          if(avcodec_open2(pCodecCtx, pCodec, &amp;optionsDict)&lt;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));
  
  
  
           sws_ctx =
  
           sws_getContext
  
      (
  
          pCodecCtx->width,
  
          pCodecCtx->height,
  
          pCodecCtx->pix_fmt,
  
          pCodecCtx->width,
  
          pCodecCtx->height,
  
          PIX_FMT_RGB24,
  
          SWS_BILINEAR,
  
          NULL,
  
          NULL,
  
          NULL
  
      );
  
  
  
    // 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, &amp;packet)>=0) {
  
      // Is this a packet from the video stream?
  
      if(packet.stream_index==videoStream) {
  
        // Decode video frame
  
        avcodec_decode_video2(pCodecCtx, pFrame, &amp;frameFinished, 
  
                 &amp;packet);
  
  
  
        // Did we get a video frame?
  
        if(frameFinished) {
  
      // Convert the image from its native format to RGB
  
          sws_scale
  
          (
  
              sws_ctx,
  
              (uint8_t const * const *)pFrame->data,
  
              pFrame->linesize,
  
              0,
  
              pCodecCtx->height,
  
              pFrameRGB->data,
  
              pFrameRGB->linesize
  
          );
  
  
  
      // Save the frame to disk
  
      if(++i&lt;=5)
  
        SaveFrame(pFrameRGB, pCodecCtx->width, pCodecCtx->height, 
  
              i);
  
        }
  
      }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_free_packet(&amp;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
  
    avformat_close_input(&amp;pFormatCtx);
  
  
  
    return 0;
  
    //getch();
  
  }

  In line :
  sprintf(szFilename, "frame%d.ppm", iFrame) ;

  I changed into frame%d.jpg. It creates .jpg file in my folder. But I can't read it. How to open this file ? Please help me.

• Getting width and height of video using flutter

  28 avril 2019, par ebg11

  I am trying to retrieve the width and height of a video using flutter. I have tried using ffmpeg

  _flutterFFmpeg.getMediaInformation(file.path);

  but the width and height are occasionally flipped. I have noticed
  "rotate" -> "90" and "displaymatrix" -> "rotation of -90.00 degrees" are present in the meta data returned.

  Is there a bug free method of using the rotate/display matrix to determine the true width/height of the video or is there a better method/library that can help me here ?

  Thanks.