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• Perspective transformations

  4 février 2009, 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 :
  

• Using FFMPEG to reliably convert videos to mp4 for iphone/ipod and flash players

  23 avril 2016, par Jake Stevenson

  I need to convert videos for use in both a flash player and the iphone/ipod touch. I’m using the following batch script with ffmpeg :

  @echo off
  
  ffmpeg.exe -i %1 -s qvga -acodec libfaac -ar 22050 -ab 128k -vcodec libx264 -threads 0 -f ipod %2

  This always outputs an mp4 file, and I can always play it on my PC. The videos also seem to play fine on my iphone 3GS. But with some input files it won’t work for older iphone versions (3G and iPod touch).

  Here’s the ffmpeg output from one such file :

  D:\ffmpeg>encode.bat d:\temp\recording.flv d:\temp\out.m4v
  
  FFmpeg version SVN-r18709, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  
    configuration: --enable-memalign-hack --prefix=/mingw --cross-prefix=i686-ming
  
  w32- --cc=ccache-i686-mingw32-gcc --target-os=mingw32 --arch=i686 --cpu=i686 --e
  
  nable-avisynth --enable-gpl --enable-zlib --enable-bzlib --enable-libgsm --enabl
  
  e-libfaac --enable-libfaad --enable-pthreads --enable-libvorbis --enable-libtheo
  
  ra --enable-libspeex --enable-libmp3lame --enable-libopenjpeg --enable-libxvid -
  
  -enable-libschroedinger --enable-libx264
  
    libavutil     50. 3. 0 / 50. 3. 0
  
    libavcodec    52.27. 0 / 52.27. 0
  
    libavformat   52.32. 0 / 52.32. 0
  
    libavdevice   52. 2. 0 / 52. 2. 0
  
    libswscale     0. 7. 1 /  0. 7. 1
  
    built on Apr 28 2009 04:04:42, gcc: 4.2.4
  
  [flv @ 0x187d650]skipping flv packet: type 18, size 164, flags 0
  
  Input #0, flv, from 'd:\temp\recording.flv':
  
    Duration: 00:00:07.17, start: 0.001000, bitrate: N/A
  
      Stream #0.0: Video: flv, yuv420p, 320x240, 1k tbr, 1k tbn, 1k tbc
  
      Stream #0.1: Audio: nellymoser, 44100 Hz, mono, s16
  
  [libx264 @ 0x13518b0]using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE
  
  4.2
  
  [libx264 @ 0x13518b0]profile Baseline, level 4.2
  
  Output #0, ipod, to 'd:\temp\out.m4v':
  
      Stream #0.0: Video: libx264, yuv420p, 320x240, q=2-31, 200 kb/s, 1k tbn, 1k
  
  tbc
  
      Stream #0.1: Audio: libfaac, 22050 Hz, mono, s16, 128 kb/s
  
  Stream mapping:
  
    Stream #0.0 -> #0.0
  
    Stream #0.1 -> #0.1
  
  Press [q] to stop encoding
  
  frame=   90 fps=  0 q=-1.0 Lsize=     128kB time=6.87 bitrate= 152.4kbits/s
  
  video:92kB audio:32kB global headers:1kB muxing overhead 2.620892%
  
  [libx264 @ 0x13518b0]slice I:8     Avg QP:29.62  size:  7047
  
  [libx264 @ 0x13518b0]slice P:82    Avg QP:30.83  size:   467
  
  [libx264 @ 0x13518b0]mb I  I16..4: 17.9%  0.0% 82.1%
  
  [libx264 @ 0x13518b0]mb P  I16..4:  0.6%  0.0%  0.0%  P16..4: 23.1%  0.0%  0.0%
  
   0.0%  0.0%    skip:76.3%
  
  [libx264 @ 0x13518b0]final ratefactor: 57.50
  
  [libx264 @ 0x13518b0]SSIM Mean Y:0.9544735
  
  [libx264 @ 0x13518b0]kb/s:8412.6

  My suspicion is that it has something to do with the audio encoding. If so, does anyone know how to force it to reencode the audio to the proper format ?

  Any other ideas ?

• The First Problem

  19 janvier 2011, par Multimedia Mike — HTML5

  A few years ago, The Linux Hater made the following poignant observation regarding Linux driver support :

  Drivers are only just the beginning... But for some reason y’all like to focus on the drivers. You know why lusers do that ? Because it just happens to be the problem that people notice first.

  And so it is with the HTML5 video codec debate, re-invigorated in the past week by Google’s announcement of dropping native H.264 support in their own HTML5 video tag implementation. As I read up on the fiery debate, I kept wondering why people are so obsessed with this issue. Then I remembered the Linux Hater’s post and realized that the video codec issue is simply the first problem that most people notice regarding HTML5 video.

  I appreciate that the video codec debate has prompted Niedermayer to post on his blog once more. Otherwise, I’m just munching popcorn on the sidelines, amused and mildly relieved that the various factions are vociferously attacking each other rather than that little project I help with at work.

  Getting back to the "first problem" aspect— there’s so much emphasis on the video codec ; I wonder why no one ever, ever mentions word one about an audio codec. AAC is typically the codec that pairs with H.264 in the MPEG stack. Dark Shikari once mentioned that "AAC’s licensing terms are exponentially more onerous than H.264′s. If Google didn’t want to use H.264, they would sure as hell not want to use AAC." Most people are probably using "H.264" to refer to the entire MPEG/H.264/AAC stack, even if they probably don’t understand what all of those pieces mean.

  Anyway, The Linux Hater’s driver piece continues :

  Once y’all have drivers, the fight will move to the next layer up. And like I said, it’s a lot harder at that layer.

  A few months ago, when I wanted to post the WebM output of my new VP8 encoder and thought it would be a nice touch to deliver it via a video tag, I ignored the video codec problem (just encoded a VP8/WebM file) only to immediately discover a problem at a different layer— specifically, embedding a file using a video tag triggers a full file download when the page is loaded, which is unacceptable from end user and web hosting perspectives. This is a known issue but doesn’t get as much attention, I guess because there are bigger problems to solve first (c.f. video codec issue).

  For other issues, check out the YouTube blog’s HTML5 post or Hulu’s post that also commented on HTML5. Issues such as video streaming flexibility, content protection, fullscreen video, webcam/microphone input, and numerous others are rarely mentioned in the debates. Only "video codec" is of paramount importance.

  But I’m lending too much weight to the cacophony of a largely uninformed internet debate. Realistically, I know there are many talented engineers down in the trenches working to solve at least some of these problems. To tie this in with the Linux driver example, I’m consistently stunned these days regarding how simple it is to get Linux working on a new computer— most commodity consumer hardware really does just work right out of the box. Maybe one day, we’ll wake up and find that HTML5 video has advanced to the point that it solves all of the relevant problems to make it the simple and obvious choice for delivering web video in nearly all situations.

  It won’t be this year.