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• FFMPEG Generate N Evenly Spaced PNG Screenshots

  21 août 2023, par Kevin Sylvestre

  I am trying to generate 8 screenshots for an uploaded video using FFMPEG. I currently have :

  



  


  ffmpeg -i Trailer-720p.mov -r .2
 -vcodec png Preview-%d.png

  


  



  Which generates a screenshot every 5 seconds. How can I add the ability to generate a screenshot for frames distributed over a percentage of total time. Thanks. Furthermore, is it possible to generate a screenshot at 50% for example ? Thanks.

  


• Revision 1ed0e1beb5 : Move SVC per-frame loop from sample app into libvpx proper SVC multiple layer p

  23 octobre 2013, par Ivan Maltz

  Changed Paths :
   Modify /examples.mk

  
   Modify /libs.mk

  
   Add /test/svc_test.cc

  
   Modify /test/test.mk

  
   Modify /vp9/common/vp9_onyx.h

  
   Modify /vp9/encoder/vp9_onyx_if.c

  
   Modify /vp9/vp9_cx_iface.c

  
   Modify /vp9_spatial_scalable_encoder.c

  
   Modify /vpx/exports_enc

  
   Add /vpx/src/svc_encodeframe.c

  
   Add /vpx/svc_context.h

  
   Modify /vpx/vp8cx.h

  
   Modify /vpx/vpx_codec.mk

  
  
  Move SVC per-frame loop from sample app into libvpx proper

  SVC multiple layer per frame encoding is invoked with vpx_svc_init and
  vpx_svc_encode. These interfaces are designed to be invoked from ffmpeg.
  Additional improvements :
   make dummy frame handling a bit more explicit
   fixed bug with single layer encodes
   track individual frame sizes and psnrs instead of averages
   parameterized quantizer, 16th scalefactors, more logging,
   enabled single layer encodes to generate baseline
   include new mode for 3 layer I frame with 5 total layers

  Change-Id : I46cfa600d102e208c6af8acd6132e0cc25cda8d4

• Writing a series of images into a video file using libavcodec (ffmpeg)

  19 novembre 2013, par user2978372

  Requirements :

  I have a bunch of images (to be more specific they are 1024x768, 24bpp RGB PNG files) that I want to encode into a video files.

  And I need to use 'libavcodec' library, not 'ffmpeg' tool. (well I know they are basically same in the origin, I am emphasizing because someone may answer to use 'ffmpeg' tool, but that's not a solution what I am looking for)

  I am using h264 encoder.

  Target :
  A high quality video with equal resolution (1024 x 768), YUV420P
  each image has a duration of 1 second.
  24 fps

  Problems :
  i've tried with many different (but same resolution and bits) png images, and all have failed to output a good video.

  For some series of images, only the frames of first second was shown in a good shape, but the remaining frames was distorted and color changed (lighter).

  For some series of images, it seemed the images were zoomed-in and distorted again.

  and etc.

  Question :
  I am a total AV newbie and I need someone to verify my steps for encoding. I am total AV newbie.

  1) av_register_all()

  2) avcodec_register_all()

  3) avcodec_find_encoder()

  4) avcodec_alloc_context3()

  5) sets codec configuraton to context.

  6) avcodec_open2()

  7) opens a output file using fopen_s()

  8)

  for(int second=1; second<=10; ++seconds)
  
  {
  
  
  
    Read a image from local using Gdiplus
  
  
  
    Create a gdiplus bitmap and draw the image onto this bitmap
  
  
  
    Get the raw byte data using LockBits
  
  
  
    Transfer this RGB raw byte into YUV420 frame using 'swscontext', 'sws_scale'
  
  
  
    for(int f=0; f<24; ++f)
  
    {
  
      av_init_packet(&pkt);
  
      pkt.data = NULL;
  
      pkt.size = 0;
  
  
  
      pFrame->pts = f;
  
      ret = avcodec_encode_video2(pContext, &pkt, pFrame, &got_output);
  
  
  
      if(got_output)
  
      {
  
          fwrite(pkt.data, 1, pkt.size, outputFile);
  
          av_free_packet(&pkt);
  
      }
  
    }
  
  }
  
  
  
  /* get the delayed frames */
  
  for (got_output = 1; got_output; i++) {
  
      fflush(stdout);
  
  
  
      ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
  
      if (ret < 0) {
  
          fprintf(stderr, "Error encoding frame\n");
  
          exit(1);
  
      }
  
  
  
      if (got_output) {
  
          printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
          fwrite(pkt.data, 1, pkt.size, f);
  
          av_free_packet(&pkt);
  
      }
  
  }
  
  
  
  close everything required

  I am sure that I misunderstood some steps using ffmpeg api. The above pseudo codes are based on the 'encoding' example of ffmpeg. which part am I doing wrong ? please can someone help me ?

  p.s sorry about broken english. english is not my natvie language. I tried my best =P