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• Perspective transformations

  9 juin 2010, par Mikko Koppanen — Imagick, PHP stuff

  Finally (after a long break) I managed to force myself to update the PHP documentation and this time it was distortImage code example. Things have been hectic lately but that does not quite explain the 6 months(?) break between this and the previous post. As a matter of a fact there is no excuse for such a long silence so I will try to update this blog a bit more often from now on.

  Back in the day I used to blog the examples and update the documentation if I remembered but I am trying to fix this bad habit. Most of the latest examples have been updated in to the manual. In the case of the two last examples I updated the documentation first and then blogged on the subject.

  I took some time to actually understand the perspective transformations properly using the excellent ImageMagick examples (mainly created by Anthony Thyssen) as a reference. The basic idea of perspective distortion seems simple : to distort the control points to new locations. Grabbing the syntax for Imagick was easy, an array of control point pairs in the form of :

  php

  < view plain text >

  1. array(source_x, source_y, dest_x, dest_y ... )

  The following example uses the built-in checkerboard pattern to demonstrate perspective distortion :

  php

  < view plain text >

  1. < ?php
  2. /* Create new object */
  3. $im = new Imagick() ;
  4.  
  5. /* Create new checkerboard pattern */
  6. $im->newPseudoImage(100, 100, "pattern:checkerboard") ;
  7.  
  8. /* Set the image format to png */
  9. $im->setImageFormat(’png’) ;
  10.  
  11. /* Fill background area with transparent */
  12. $im->setImageVirtualPixelMethod(Imagick: :VIRTUALPIXELMETHOD_TRANSPARENT) ;
  13.  
  14. /* Activate matte */
  15. $im->setImageMatte(true) ;
  16.  
  17. /* Control points for the distortion */
  18. $controlPoints = array( 10, 10,
  19.             10, 5,
  20.  
  21.             10, $im->getImageHeight() - 20,
  22.             10, $im->getImageHeight() - 5,
  23.  
  24.             $im->getImageWidth() - 10, 10,
  25.             $im->getImageWidth() - 10, 20,
  26.  
  27.             $im->getImageWidth() - 10, $im->getImageHeight() - 10,
  28.             $im->getImageWidth() - 10, $im->getImageHeight() - 30) ;
  29.  
  30. /* Perform the distortion */ 
  31. $im->distortImage(Imagick: :DISTORTION_PERSPECTIVE, $controlPoints, true) ;
  32.  
  33. /* Ouput the image */ 
  34. header("Content-Type : image/png") ;
  35. echo $im ;
  36.  ?>

  Here is the source image :
  

  And the result :
  

• lavc : Deprecate avctx.rtp_callback field

  19 novembre 2015, par Vittorio Giovara

  lavc : Deprecate avctx.rtp_callback field
  This function returns the encoded data of a frame, one slice at a time
  
  directly when that slice is encoded, instead of waiting for the full
  
  frame to be done. However this field has a debatable usefulness, since
  
  it looks like it is just a convoluted way to get data at lowest
  
  possible latency, or a somewhat hacky way to store h263 in RFC-2190
  
  rtp encapsulation.
  Moreover when multi-threading is enabled (which is by default) the order
  
  of returned slices is not deterministic at all, making the use of this
  
  function not reliable at all (or at the very least, more complicated
  
  than it should be).
  So, for the reasons stated above, and being used by only a single encoder
  
  family (mpegvideo), this field is deemed unnecessary, overcomplicated,
  
  and not really belonging to libavcodec. Libavformat features a complete
  
  implementation of RFC-2190, for any other case.
  Signed-off-by : Vittorio Giovara <vittorio.giovara@gmail.com>
  

  • [DBH] doc/APIchanges
  • [DBH] libavcodec/avcodec.h
  • [DBH] libavcodec/mpegvideo_enc.c
  • [DBH] libavcodec/version.h

• ffmpeg : unable to cut avi movie

  10 mars 2016, par ird

  I am using ffmpeg to cut video file :

  ffmpeg -<inputfile> -ss 00:00:00 -t 00:00:30 <outputfile>
  
  </outputfile></inputfile>

  It’s OK for different file formats exclude *.avi format. For avi movies ffmpeg shows that video is truncated, but output file contains full video (without truncating).
  Does anybody know possible ways for problem troubleshooting ?

  Here converting command output for avi file :

  FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  
    built on Feb  1 2011 02:54:36 with gcc 4.4.5
  
    configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-x11grab
  
    libavutil     50.36. 0 / 50.36. 0
  
    libavcore      0.16. 1 /  0.16. 1
  
    libavcodec    52.108. 0 / 52.108. 0
  
    libavformat   52.93. 0 / 52.93. 0
  
    libavdevice   52. 2. 3 / 52. 2. 3
  
    libavfilter    1.74. 0 /  1.74. 0
  
    libswscale     0.12. 0 /  0.12. 0
  
    libpostproc   51. 2. 0 / 51. 2. 0
  
  [mpeg4 @ 0x91e7e10] Invalid and inefficient vfw-avi packed B frames detected
  
  
  
  Seems stream 0 codec frame rate differs from container frame rate: 30000.00 (30000/1) -> 25.00 (25/1)
  
  Input #0, avi, from '/home/mightymeeting/Videos/tam-19.avi':
  
    Duration: 00:04:43.32, start: 0.000000, bitrate: 564 kb/s
  
      Stream #0.0: Video: mpeg4, yuv420p, 352x208 [PAR 1:1 DAR 22:13], 25 fps, 25 tbr, 25 tbn, 30k tbc
  
      Stream #0.1: Audio: mp3, 32000 Hz, 2 channels, s16, 80 kb/s
  
  [buffer @ 0x91e6ed0] w:352 h:208 pixfmt:yuv420p
  
  Output #0, avi, to 'out.avi':
  
    Metadata:
  
      ISFT            : Lavf52.93.0
  
      Stream #0.0: Video: mpeg4, yuv420p, 352x208 [PAR 1:1 DAR 22:13], q=2-31, 200 kb/s, 25 tbn, 25 tbc
  
      Stream #0.1: Audio: mp2, 32000 Hz, 2 channels, s16, 64 kb/s
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
    Stream #0.1 -> #0.1
  
  Press [q] to stop encoding
  
  [mpeg4 @ 0x91e7e10] Invalid and inefficient vfw-avi packed B frames detected
  
  frame= 7082 fps=999 q=2.0 Lsize=    7513kB time=30.02 bitrate=2049.8kbits/s dup=0 drop=1    
  
  video:7079kB audio:235kB global headers:0kB muxing overhead 2.718192%