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• How to display image for particular time in a video using ffmpeg

  18 juin 2013, par Pratik Bhingardeve

  I am trying to created a video from the sequence of images. But i have to display each image with different numbers of seconds. How to do this with FFMPEG.

  Thanks in advance.

• Understanding FFMPEG Video Encoding

  20 juin 2014, par SetSlapShot

  Got this from the encoding example in ffmpeg. I can somewhat follow the authors example for audio encoding, but I find myself befuddled looking at the C code (I commented in block numbers to help me reference what I’m talking about)...

  static void video_encode_example(const char *filename)
  
  {
  
  AVCodec *codec;
  
  AVCodecContext *c= NULL;
  
  int i, out_size, size, x, y, outbuf_size;
  
  FILE *f;
  
  AVFrame *picture;
  
  uint8_t *outbuf, *picture_buf;              //BLOCK ONE
  
  printf("Video encoding\n");
  
  
  
  /* find the mpeg1 video encoder */
  
  codec = avcodec_find_encoder(CODEC_ID_MPEG1VIDEO);
  
  if (!codec) {
  
      fprintf(stderr, "codec not found\n");
  
      exit(1);                                //BLOCK TWO
  
  }
  
  
  
  c= avcodec_alloc_context();
  
  picture= avcodec_alloc_frame();
  
  /* put sample parameters */
  
  c->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  c->width = 352;
  
  c->height = 288;
  
  /* frames per second */
  
  c->time_base= (AVRational){1,25};
  
  c->gop_size = 10; /* emit one intra frame every ten frames */
  
  c->max_b_frames=1;
  
  c->pix_fmt = PIX_FMT_YUV420P;                   //BLOCK THREE
  
  
  
  /* open it */
  
  if (avcodec_open(c, codec) < 0) {
  
      fprintf(stderr, "could not open codec\n");
  
      exit(1);
  
  }
  
  f = fopen(filename, "wb");
  
  if (!f) {
  
      fprintf(stderr, "could not open %s\n", filename);
  
      exit(1);
  
  }                                               //BLOCK FOUR
  
  
  
  /* alloc image and output buffer */
  
  outbuf_size = 100000;
  
  outbuf = malloc(outbuf_size);
  
  size = c->width * c->height;
  
  picture_buf = malloc((size * 3) / 2); /* size for YUV 420 */
  
  picture->data[0] = picture_buf;
  
  picture->data[1] = picture->data[0] + size;
  
  picture->data[2] = picture->data[1] + size / 4;
  
  picture->linesize[0] = c->width;
  
  picture->linesize[1] = c->width / 2;
  
  picture->linesize[2] = c->width / 2;              //BLOCK FIVE
  
  
  
  /* encode 1 second of video */
  
  for(i=0;i<25;i++) {
  
      fflush(stdout);
  
      /* prepare a dummy image */
  
      /* Y */
  
      for(y=0;yheight;y++) {
  
          for(x=0;xwidth;x++) {
  
              picture->data[0][y * picture->linesize[0] + x] = x + y + i * 3;
  
          }
  
      }                                            //BLOCK SIX
  
  
  
      /* Cb and Cr */
  
      for(y=0;yheight/2;y++) {
  
          for(x=0;xwidth/2;x++) {
  
              picture->data[1][y * picture->linesize[1] + x] = 128 + y + i * 2;
  
              picture->data[2][y * picture->linesize[2] + x] = 64 + x + i * 5;
  
          }
  
      }                                           //BLOCK SEVEN
  
  
  
      /* encode the image */
  
      out_size = avcodec_encode_video(c, outbuf, outbuf_size, picture);
  
      printf("encoding frame %3d (size=%5d)\n", i, out_size);
  
      fwrite(outbuf, 1, out_size, f);
  
  }                                              //BLOCK EIGHT
  
  
  
  /* get the delayed frames */
  
  for(; out_size; i++) {
  
      fflush(stdout);
  
      out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL);
  
      printf("write frame %3d (size=%5d)\n", i, out_size);
  
      fwrite(outbuf, 1, out_size, f);
  
  }                                             //BLOCK NINE
  
  
  
  /* add sequence end code to have a real mpeg file */
  
  outbuf[0] = 0x00;
  
  outbuf[1] = 0x00;
  
  outbuf[2] = 0x01;
  
  outbuf[3] = 0xb7;
  
  fwrite(outbuf, 1, 4, f);
  
  fclose(f);
  
  free(picture_buf);
  
  free(outbuf);
  
  avcodec_close(c);
  
  av_free(c);
  
  av_free(picture);
  
  }                                            //BLOCK TEN

  Here’s what I can get from the authors code block by block...

  BLOCK ONE : Initializing Variables and pointers. I couldn’t find the AVFrame struct yet in the ffmpeg source code so I don’t know what its referencing

  BLOCK TWO : Uses a codec from the file, if not found close.

  BLOCK THREE : Sets sample video parameters. Only thing I don’t really get is gop size. I read about intra frames and I still don’t get what they are.

  BLOCK FOUR : Open the file for writing...

  BLOCK FIVE : Here’s where they really start losing me. Part is probably because I don’t know exactly what AVFrame is, but why do they only use 3/2 of the image size ?

  BLOCK SIX & SEVEN : I don’t understand what they are trying to accomplish with this math.

  BLOCK EIGHT : It looks like the avcodec function does all the work here, not concerned with that for the time being..

  BLOCK NINE : Since it’s outside the 25 frame for loop I assume it gets the leftover frames ?

  BLOCK TEN : Close, free mem, etc...

  I know this is a large block of code to be confused with, any input would be helpful. I got put in over my head at work. Thanks in advance SO.

• FFMPEG in Java (runtime error)

  4 juillet 2012, par Eric

  I want to write a program that converts video into frames using FFMPEG. When I use it on the Ubuntu terminal, it works fine. But when I try to put it into the Java code, it gives me a runtime error. Did I make a mistake in my code below ?

  import java.util.*;
  
  import java.awt.*;
  
  import java.lang.*;
  
  import java.lang.Runtime;
  
  import java.io.*;
  
  import java.io.IOException;
  
  
  
  public class ConvertVideoToImage
  
  {
  
      private SingletonServer ss = null;
  
  
  
      public ConvertVideoToImage(SingletonServer ss)
  
      {
  
          this.ss = ss;
  
      }
  
  
  
      public void run()
  
      {
  
          convertVideo();
  
      }
  
  
  
      public void convertVideo()
  
      {
  
          try
  
          {
  
              Runtime rt = Runtime.getRunTime().exec("ffmpeg" + "-i" +         "display.wmv" + "image%d.jpg");
  
          }
  
          catch(Exception e){}
  
      }
  
  
  
  }

  Edit :

  I have changed the code like you suggested, but it also doesn't work. And when I Googled it, I found out that someone put the full path inside the executable and it became like this :

  Runtime.getRuntime().exec("/home/pc3/Documents/ffmpeg_temp/ffmpeg -i display.wmv image%d.jpg")

  BTW, thanks for the reply. I have another question. Is it possible to make a counter for FFMPEG ? I used this command in the Ubuntu terminal to make it convert a video to 30 frames/1seconds :

  ffmpeg -i display.wmv image%d.jpg

  This will automatically generate numbers like image1.jpg, image2.jpg, to image901.jpg. Is it possible to make a counter for this ? Because I need to count the files and control the number.

  Thanks in advance.