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• What Every Programmer Should Know

  24 décembre 2012, par Multimedia Mike — General

  During my recent effort to force myself to understand Unicode and modern text encoding/processing, I was reminded that this is something that “every programmer should just know”, an idea that comes up every so often, usually in relation to a subject in which the speaker is already an expert. One of the most absurd examples I ever witnessed was a blog post along the lines of “What every working programmer ought to know about [some very specific niche of enterprise-level Java programming]“. I remember reading through the article and recognizing that I had almost no knowledge of the material. Disturbing, since I am demonstrably a “working programmer”.

  For fun, I queried the googles on the matter of what ever programmer ought to know.

  Specific Topics
  Here is what every programmer should know about : Unicode, time, memory (simple), memory (extremely in-depth), regular expressions, search engine optimization, floating point, security, basic number theory, race conditions, managed C++, VIM commands, distributed systems, object-oriented design, latency numbers, rate monotonic algorithm, merging branches in Mercurial, classes of algorithms, and human names.

  Broader Topics
  20 subjects every programmer should know, 97 things every programmer should know, 12 things every programmer should know, things every programmer should know (27 items), 10 papers every programmer should read at least twice, 10 things every programmer should know for their first job.

  Meanwhile, I remain fond of this xkcd comic whose mouseover text describes all that a person genuinely needs to know. Still, the new year is upon us, a time when people often make commitments to bettering themselves, and it couldn’t hurt (much) to at least skim some of the lists and find out what you never knew that you never knew.

  What About Multimedia ?
  Reading the foregoing (or the titles of the foregoing pieces), I naturally wonder if I should write something about what every programmer should know about multimedia. I think it would look something like a multimedia programming FAQ. These are some items that I can think of :

  1. YUV : The other colorspace (since most programmers are only familiar with RGB and have no idea what to make of the YUV that comes out of most video decoding APIs)
  2. Why you can’t easily seek randomly to any specific frame in a video file (keyframe/interframe discussion and their implications)
  3. Understand your platform before endeavoring to implement multimedia software (modern platforms, particularly mobile platforms, probably provide everything you need in the native APIs and there is likely little reason to compile libavcodec for the platform)
  4. Difference between containers and codecs (longstanding item, but I would argue it’s less relevant these days due to standardization on the MPEG — MP4/H.264/AAC — stack)
  5. What counts as a multimedia standard in this day and age (comparing the foregoing MPEG stack with the WebM/VP8/Vorbis stack)
  6. Trade-offs to consider when engineering a multimedia solution
  7. Optimization doesn’t always work the way you think it does (not everything touted as a massive speed-up in the world of computing — whether it be multithreaded CPUs, GPGPUs, new SIMD instruction sets — will necessarily be applicable to multimedia processing)
  8. A practical guide to legal issues would not be amiss
  9.  ???

  What other items count as “something multimedia-related that every programmer should know” ?

• FFmpeg returning an error - What does it mean ?

  19 mars 2013, par user1031947

  I am using FFmpeg, libmp3lame & libx264 along with the node fluent-ffmpeg module. This is my first foray into processing uploaded videos.

  From node, I use the following code to process an uploaded video :

  var proc = new ffmpeg({ source: src, nolog: true })
  
      .usingPreset( "podcast" )
  
      .withAudioCodec( "libmp3lame" )
  
      .saveToFile( dest, function( retcode, err ){
  
           if( err ) throw err;
  
           ...
  
      });

  When I try to process a video, this fails with the following error, which I don't understand. I am hoping someone here can help point me in the right direction. Thanks !

  > ffmpeg version 0.8.5-6:0.8.5-1, Copyright (c) 2000-2012 the Libav
  
  > developers   built on Jan 13 2013 12:05:48 with gcc 4.7.2
  
  > *** THIS PROGRAM IS DEPRECATED *** This program is only provided for compatibility and will be removed in a future release. Please use
  
  > avconv instead.
  
  > 
  
  > Seems stream 0 codec frame rate differs from container frame rate:
  
  > 5994.00 (5994/1) -> 29.97 (2997/100) Input #0, mov,mp4,m4a,3gp,3g2,mj2, from
  
  > '/home/ssp/resources/tmp/32111bf4217e87c23328ec81c56c7d02':  
  
  > Metadata:
  
  >     major_brand     : M4VP
  
  >     minor_version   : 1
  
  >     compatible_brands: M4VPM4A mp42isom
  
  >     creation_time   : 2008-08-26 17:28:47   Duration: 00:00:08.01, start: 0.000000, bitrate: 944 kb/s
  
  >     Stream #0.0(eng): Video: h264 (Constrained Baseline), yuv420p, 480x272, 815 kb/s, 29.97 fps, 29.97 tbr, 2997 tbn, 5994 tbc
  
  >     Metadata:
  
  >       creation_time   : 2008-08-26 17:28:47
  
  >     Stream #0.1(eng): Audio: aac, 44100 Hz, stereo, s16, 124 kb/s
  
  >     Metadata:
  
  >       creation_time   : 2008-08-26 17:28:47 [buffer @ 0xb685a0] w:480 h:272 pixfmt:yuv420p [scale @ 0xb63280] w:480 h:272 fmt:yuv420p ->
  
  > w:320 h:176 fmt:yuv420p flags:0x4 [libx264 @ 0xb67c20] VBV maxrate
  
  > unspecified, assuming CBR [libx264 @ 0xb67c20] using cpu capabilities:
  
  > MMX2 SSE2Fast SSSE3 FastShuffle SSE4.2 AVX [libx264 @ 0xb67c20]
  
  > profile Main, level 1.3 Output #0, m4v, to
  
  > '/home/ssp/resources/users/11/026468c8f4ea1beee0a585ebc2208137.m4v':  
  
  > Metadata:
  
  >     major_brand     : M4VP
  
  >     minor_version   : 1
  
  >     compatible_brands: M4VPM4A mp42isom
  
  >     creation_time   : 2008-08-26 17:28:47
  
  >     encoder         : Lavf53.21.1
  
  >     Stream #0.0(eng): Video: libx264, yuv420p, 320x176, q=10-51, 512 kb/s, 90k tbn, 29.97 tbc
  
  >     Metadata:
  
  >       creation_time   : 2008-08-26 17:28:47
  
  >     Stream #0.1(eng): Audio: libmp3lame, 44100 Hz, 1 channels, s16, 128 kb/s
  
  >     Metadata:
  
  >       creation_time   : 2008-08-26 17:28:47 Stream mapping:   Stream #0.0 -> #0.0   Stream #0.1 -> #0.1 Press ctrl-c to stop encoding frame=  240 fps=154 q=11.0 Lsize=     642kB time=7.97 bitrate=
  
  > 659.3kbits/s     video:516kB audio:126kB global headers:0kB muxing overhead 0.000000% frame I:1     Avg QP:15.35  size:  9995 [libx264 @
  
  > 0xb67c20] frame P:77    Avg QP:13.25  size:  5419 [libx264 @ 0xb67c20]
  
  > frame B:162   Avg QP:18.31  size:   625 [libx264 @ 0xb67c20]
  
  > consecutive B-frames:  2.5% 12.5% 30.0% 55.0% [libx264 @ 0xb67c20] mb
  
  > I  I16..4:  9.1%  0.0% 90.9% [libx264 @ 0xb67c20] mb P  I16..4:  2.1% 
  
  > 0.0%  2.8%  P16..4: 18.0% 29.9% 44.8%  0.0%  0.0%    skip: 2.3% [libx264 @ 0xb67c20] mb B  I16..4:  0.1%  0.0%  0.0%  B16..8: 35.2%
  
  > 20.2%  1.9%  direct:14.5%  skip:28.1%  L0:26.3% L1:38.1% BI:35.6% [libx264 @ 0xb67c20] coded y,uvDC,uvAC intra: 83.7% 91.7% 84.7% inter:
  
  > 27.7% 43.4% 13.9% [libx264 @ 0xb67c20] i16 v,h,dc,p: 20% 29% 42%  9% [libx264 @ 0xb67c20] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 17% 29% 20%  4% 
  
  > 8%  6%  9%  3%  4% [libx264 @ 0xb67c20] i8c dc,h,v,p: 60% 19% 16%  5%
  
  > [libx264 @ 0xb67c20] Weighted P-Frames: Y:2.6% UV:0.0% [libx264 @
  
  > 0xb67c20] ref P L0: 75.6% 13.5%  8.0%  2.8%  0.1% [libx264 @ 0xb67c20]
  
  > ref B L0: 94.5%  5.5% [libx264 @ 0xb67c20] kb/s:528.00

• Prendre en compte smush (scripts init)

  28 avril 2013

  Il faudrait installer les binaires nécessaires au plugin smush :

  • ImageMagick ;
  • optipng ;
  • pngnq ;
  • gifscycle ;
  • libjpeg-progs ;

  Il faut aussi ajouter le checkout du plugin.

  1. svn co svn ://zone.spip.org/spip-zone/_plugins_/smush_images/trunk plugins/smush