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• How we can open /dev/video0 or any v4l2 node with ffmpeg for capture raw frames and encode it in jpeg format ?

  19 mars 2016, par satinder

  I am new in video domain . I am working now on ffmpeg , I use ffmpeg command line but there is very big issue and challenge for use ffmpeg in my own c code .So I read some tutorials like dranger.com etc . But I am not able to capture v4l2 or my laptop /dev/video0 node . I want capture raw video stream and overlay it with some text and then compress it in jpeg format . I have a little idea and that is in following code that code is working for ant .mp4 format or encoded file but not work on /dev/video0 node format . so please any one help me . Thanks in advance !!

  please see following code snapshot that is a tutorial1.c from dranger.com :

  #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);
  
    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;
  
  
  
    if(argc &lt; 2) {
  
      printf("Please provide a movie file\n");
  
      return -1;
  
    }
  
    // Register all formats and codecs
  
    av_register_all();
  
  
  
    // Open video file
  
    if(avformat_open_input(&amp;pFormatCtx, argv[1], NULL, NULL)!=0)
  
      return -1; // Couldn't open file
  
  
  
    // Retrieve stream information
  
    if(avformat_find_stream_info(pFormatCtx, NULL)&lt;0)
  
      return -1; // Couldn't find stream information
  
  
  
    // Dump information about file onto standard error
  
    av_dump_format(pFormatCtx, 0, argv[1], 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'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_open2(pCodecCtx, pCodec, &amp;optionsDict)&lt;0)
  
      return -1; // Could not open codec
  
  
  
    // Allocate video frame
  
    pFrame=av_frame_alloc();
  
  
  
    // Allocate an AVFrame structure
  
    pFrameRGB=av_frame_alloc();
  
    if(pFrameRGB==NULL)
  
      return -1;
  
  
  
    // Determine required buffer size and allocate buffer
  
    numBytes=avpicture_get_size(AV_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,
  
          AV_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, AV_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;
  
  }

• Torn images acquired when decoding video frames with FFmpeg

  22 mars 2016, par bot1131357

  I am trying to decode the images using the tutorial at dranger.com. Below is the code I’m working with. The code is pretty much untouched aside from pgm_save() function and replacing the deprecated functions.

  The program compiled successfully, but when I tried to process a video, I’m getting tearing effect like this : image1 and this image2.

  (Side question : I’ve tried to replace avpicture_fill() which is deprecated with av_image_copy_to_buffer() but I’m getting an access violation error, so I left it as is. I wonder if there is a proper way for me to assign the frame data to a buffer.)

  The library that I’m using is ffmpeg-20160219-git-98a0053-win32-dev. Would really appreciate it if someone could help me with this.

  // Decode video and save frames
  
  
  
  char filename[] = "test%0.3d.ppm";
  
  static void ppm_save(unsigned char *buf, int wrap, int xsize, int ysize,
  
                       int framenum )
  
  {
  
  
  
      char filenamestr[sizeof(filename)];
  
      FILE *f;
  
      int i;
  
  
  
      sprintf_s(filenamestr, sizeof(filenamestr), filename, framenum);
  
      fopen_s(&f,filenamestr,"w");
  
      fprintf(f,"P6\n%d %d\n%d\n",xsize,ysize,255);
  
      for(i=0;i/ Register all formats and codecs
  
      av_register_all();
  
  
  
      // Open video file
  
      if (avformat_open_input(&pFormatCtx, argv[1], NULL, NULL) != 0)
  
          return -1; // Couldn't open file
  
  
  
      // Retrieve stream information
  
      if (avformat_find_stream_info(pFormatCtx, NULL) < 0)
  
          return -1; // Couldn't find stream information
  
  
  
      // Dump information about file onto standard error (Not necessary)
  
      av_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 == AVMEDIA_TYPE_VIDEO) {
  
              videoStream = i;
  
              break;
  
          }
  
      if (videoStream == -1)
  
          return -1; // Didn't find a video stream
  
  
  
      /* find the video decoder */
  
      codec = avcodec_find_decoder(pFormatCtx->streams[videoStream]->codec->codec_id);
  
      if (!codec) {
  
          fprintf(stderr, "codec not found\n");
  
          exit(1);
  
      }
  
  
  
      codecCtx= avcodec_alloc_context3(codec);
  
      if(avcodec_copy_context(codecCtx, pFormatCtx->streams[i]->codec) != 0) {
  
          fprintf(stderr, "Couldn't copy codec context");
  
          return -1; // Error copying codec context
  
      }   
  
  
  
      /* open it */
  
      if (avcodec_open2(codecCtx, codec, NULL) < 0) {
  
          fprintf(stderr, "could not open codec\n");
  
          exit(1);
  
      }
  
  
  
      // Allocate video frame
  
      inframe= av_frame_alloc();
  
      if(inframe==NULL)
  
          return -1;
  
  
  
      // Allocate output frame
  
      outframe=av_frame_alloc();
  
      if(outframe==NULL)
  
          return -1;
  
  
  
      // Determine required buffer size and allocate buffer
  
      int numBytes=av_image_get_buffer_size(AV_PIX_FMT_RGB24, codecCtx->width,
  
                      codecCtx->height,1);
  
      uint8_t* buffer=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
  
  
  
      // Assign appropriate parts of buffer to image planes in outframe
  
      // Note that outframe is an AVFrame, but AVFrame is a superset
  
      // of AVPicture
  
  
  
  
  
      avpicture_fill((AVPicture *)outframe, buffer, AV_PIX_FMT_RGB24,
  
           codecCtx->width, codecCtx->height );
  
      //av_image_copy_to_buffer(buffer, numBytes,
  
   //                           outframe->data, outframe->linesize,
  
   //                           AV_PIX_FMT_RGB24, codecCtx->width, codecCtx->height,1);
  
  
  
      // initialize SWS context for software scaling
  
      sws_ctx = sws_getContext(codecCtx->width,
  
                 codecCtx->height,
  
                 codecCtx->pix_fmt,
  
                 codecCtx->width,
  
                 codecCtx->height,
  
                 AV_PIX_FMT_RGB24,
  
                 SWS_BILINEAR,
  
                 NULL,
  
                 NULL,
  
                 NULL
  
                 );   
  
  
  
  
  
      // av_init_packet(&avpkt);
  
  
  
  
  
      i = 0;
  
      while(av_read_frame(pFormatCtx, &avpkt)>=0) {
  
          // Is this a packet from the video stream?
  
          if(avpkt.stream_index==videoStream) {
  
            // Decode video frame
  
            avcodec_decode_video2(codecCtx, inframe, &frameFinished, &avpkt);
  
  
  
            // 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 *)inframe->data,
  
                inframe->linesize, 0, codecCtx->height,
  
                outframe->data, outframe->linesize);
  
  
  
          // Save the frame to disk
  
          if(++i%15 == 0)
  
              ppm_save(outframe->data[0], outframe->linesize[0], 
  
                          codecCtx->width, codecCtx->height, i);
  
  
  
            }
  
          }
  
  
  
      // Free the packet that was allocated by av_read_frame
  
      av_packet_unref(&avpkt);
  
      }
  
  
  
  
  
      // Free the RGB image
  
      av_free(buffer);
  
      av_frame_free(&outframe);
  
  
  
      // Free the original frame
  
      av_frame_free(&inframe);
  
  
  
      // Close the codecs
  
      avcodec_close(codecCtx);
  
      av_free(codecCtx);
  
  
  
      // Close the video file
  
      avformat_close_input(&pFormatCtx);
  
  
  
  
  
      printf("\n");
  
  
  
  
  
      return 0;
  
  }

• ffmpeg convertation imagevideo causes artefacts

  24 mars 2016, par mrgloom

  I want to convert video to images, do some image processing and convert images back to video.

  Here is my commands :

  ./ffmpeg -r 30 -i $VIDEO_NAME "image%d.png"
  
  
  
  ./ffmpeg -r 30 -y -i "image%d.png" output.mpg

  But in output.mpg video I have some artefacts like in jpeg.

  Also I don’t know how to detrmine fps, I set fps=30 (-r 30).
  When I use above first command without -r it produces a lot of images > 1kk, but than I use -r 30 option it produce same number of images as this command calculationg number of frames :

  FRAME_COUNT=`./ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 $VIDEO_NAME`

  So my questions are :

  1. How to determine frame rate ?

  2. How to convert images to video and don’t reduce initial quality ?

  UPDATE :

  Seems this helped, after I removed -r option
  Image sequence to video quality

  so resulting command is :

  ./ffmpeg -y -i "image%d.png" -vcodec mpeg4 -b $BITRATE output_$BITRATE.avi

  but I’m still not sure how to select bitrate.

  How can I see bitrate of original .mp4 file ?