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• Calculate frames to remove to get timelapse of desired length

  12 juin 2016, par Espen Birk

  I’ve got lots of images stored on a server, and a reference in a MySQL database so that i can easily query it for image from specific dates/time.

  Images is taken with an interval of 7 images/hour.

  Lets say i want to create a timelapse from the last 4 days, and make a 5 sec movie. How can i calculate how to evenly drop frames to get to that desired length of 5 seconds ?

  This is what i got so far.

  Total images : 4 Days * 24 hours * 7 images/hour = 672 images
  Required images at 24 fps : 24 * 5 = 120 images

  Divide the total images with the required images to find out which/every frame i need to keep

  672 / 120 = 5.6

  Then i loop trough all 672 images, and every 5th or 6th time i store a reference to the image in an array.

  Here is my problem. If i round up i get a video thats longer than i want, and if i round down i get a video thats shorter.

  If i keep every 5th image when looping : 134 images / 24 fps = 5.6 sec video
  If i keep every 6th image when looping : 112 images / 24 fps = 4.6 sec video

  Is it possible to get it better, and still skip images evenly ?

  Solved this using xxfelixxx’s answer in PHP
  Heres the code in PHP :

  $start  = 1;
  
  $stop   = 672; // Total Images
  
  
  
  $dur    = 5;   // Video Duration
  
  $n      = 24 * $dur; // Required frames - 24 FPS * Duration
  
  $next   = $start;
  
  $step = ( $stop - $start ) / $n;
  
  
  
  $frames = array();
  
  
  
  for ($i = 1; $i <= $n; $i++) {
  
      $frames[] = round($next);
  
      $next += $step;
  
  };
  
  
  
  var_dump($frames);

• x86 : use emms after ff_int32_to_float_fmul_scalar_sse

  29 décembre 2015, par Janne Grunau

  x86 : use emms after ff_int32_to_float_fmul_scalar_sse
  Intel’s Instruction Set Reference (as of September 2015) clearly states
  
  that cvtpi2ps switches to MMX state. Actual CPUs do not switch if the
  
  source is a memory location. The Instruction Set Reference from 1999
  
  (Order Number 243191) describes this behaviour but all later versions
  
  I’ve seen have make no distinction whether MMX registers or memory is
  
  used as source.
  
  The documentation for the matching SSE2 instruction to convert to double
  
  (cvtpi2pd) was fixed (see the valgrind bug
  
  https://bugs.kde.org/show_bug.cgi?id=210264).
  It will take time to get a clarification and fixes in place. In the
  
  meantime it makes sense to change ff_int32_to_float_fmul_scalar_sse to
  
  be correct according to the documentation. The vast majority of users
  
  will have SSE2 so a change to the SSE version has little effect.
  Fixes fate-checkasm on x86 valgrind targets.
  Valgrind ’bug’ reported as https://bugs.kde.org/show_bug.cgi?id=357059
  

  • [DBH] libavcodec/x86/fmtconvert.asm

• FFmpeg error : ratecontrol_init : can't open stats file

  18 décembre 2015, par oldo.nicho

  I’ve setup an AWS EC2 instance running Ubuntu 14.04 and have installed FFmpeg so that I can compress and transcode video.

  I’m trying to do a two pass conversion with the following code :

  ffmpeg -i input-file.avi -codec:v libx264 -profile:v high -preset slow -b:v 500k -maxrate 500k -bufsize 1000k -vf scale=702:-1 -threads 0 -pass 1 -an -f mp4 ~/encoded/null

  and second pass :

  ffmpeg -i input-file.avi -codec:v libx264 -profile:v high -preset slow -b:v 500k -maxrate 500k -bufsize 1000k -vf scale=702:-1 -threads 0 -pass 2 -codec:a libfdk_aac -b:a 128k -f mp4 output-file.mp4

  However I get the following error :

  ffmpeg version N-77283-g91c2a33 Copyright (c) 2000-2015 the FFmpeg developers
  
    built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04)
  
    configuration: --prefix=/home/ubuntu/ffmpeg_build --pkg-config-flags=--static --extra-cflags=-I/home/ubuntu/ffmpeg_build/include --extra-ldflags=-L/home/ubuntu/ffmpeg_build/lib --bindir=/home/ubuntu/bin --enable-gpl --enable-libass --enable-libfdk-aac --enable-libfreetype --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libx264 --enable-nonfree
  
    libavutil      55. 11.100 / 55. 11.100
  
    libavcodec     57. 17.100 / 57. 17.100
  
    libavformat    57. 20.100 / 57. 20.100
  
    libavdevice    57.  0.100 / 57.  0.100
  
    libavfilter     6. 21.100 /  6. 21.100
  
    libswscale      4.  0.100 /  4.  0.100
  
    libswresample   2.  0.101 /  2.  0.101
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Input #0, avi, from 'input-file.avi':
  
    Duration: 01:18:05.29, start: 0.000000, bitrate: 2025 kb/s
  
      Stream #0:0: Video: mpeg4 (Simple Profile) (XVID / 0x44495658), yuv420p, 720x480 [SAR 1:1 DAR 3:2], 1789 kb/s, 29.97 fps, 29.97 tbr, 29.97 tbn, 29.97 tbc
  
      Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, stereo, fltp, 224 kb/s
  
  [libx264 @ 0x1e04240] using SAR=1/1
  
  [libx264 @ 0x1e04240] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX AVX2 FMA3 LZCNT BMI2
  
  [libx264 @ 0x1e04240] ratecontrol_init: can't open stats file
  
  Output #0, mp4, to '/home/ubuntu/encoded/null':
  
      Stream #0:0: Video: h264, none, q=2-31, 128 kb/s, SAR 1:1 DAR 0:0, 29.97 fps
  
      Metadata:
  
        encoder         : Lavc57.17.100 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg4 (native) -> h264 (libx264))
  
  Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height

  The command as written above works fine on my local computer (running OSX). Would anyone have any suggestions as to how to fix this problem ?