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• Unable to save Matplotlib animations using ffmpeg

  23 décembre 2017, par jtpointon

  I have installed ffmpeg and added it to path, and checked it works in command prompt, but I am still unable to save animations. I have tried creating a sin wave that will animate when I don’t try to save it, but throws an error when I do to demonstrate ;

  from __future__ import division
  
  
  
  import numpy as numpy
  
  from matplotlib import pyplot as pyplot
  
  from matplotlib import animation
  
  
  
  fig = pyplot.figure()
  
  ax = pyplot.axes(xlim=(0, 2), ylim=(-2, 2))
  
  line, = ax.plot([], [], lw=2)
  
  
  
  def init():
  
      line.set_data([], [])
  
      return line,
  
  
  
  def animate(i):
  
      x = numpy.linspace(0, 2, 1000)
  
      y = numpy.sin(2 * numpy.pi * (x - 0.01 * i))
  
      line.set_data(x, y)
  
      return line,
  
  
  
  anim = animation.FuncAnimation(fig, animate, init_func=init, frames=200, 
  
      interval=20, blit=True, repeat=False)
  
  
  
  FFwriter = animation.FFMpegWriter()
  
  anim.save('animation_testing.mp4', writer = FFwriter)
  
  
  
  pyplot.show()

  When I try to run this it throws the same errors over and over again, I assume as it iterates through each frame ;

  Traceback (most recent call last):
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\backends\backend_wx.py", line 212, in _on_timer
  
      TimerBase._on_timer(self)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\backend_bases.py", line 1273, in _on_timer
  
      ret = func(*args, **kwargs)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 910, in _step
  
      still_going = Animation._step(self, *args)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 769, in _step
  
      self._draw_next_frame(framedata, self._blit)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 787, in _draw_next_frame
  
      self._pre_draw(framedata, blit)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 800, in _pre_draw
  
      self._blit_clear(self._drawn_artists, self._blit_cache)
  
    File "c:\users\james\appdata\local\enthought\canopy\user\lib\site-
  
  packages\matplotlib\animation.py", line 840, in _blit_clear
  
      a.figure.canvas.restore_region(bg_cache[a])
  
  KeyError: 

  Since it mentioned an error in _blit_clear I tried changing blit to False in FuncAnimation, but then it wouldn’t animate in the pyplot.show() when I didn’t try to save.

  I’m unsure as to where the error could be and so can’t work out how to fix this.

  I’m using Windows 10, python 2.7.6 and matplotlib version 1.4.2

  Many Thanks !

• undefined reference to 'main' in Android.mk file with NDK

  25 juillet 2015, par Laurent Gorse

  I’m trying to recompile a native ffmpeg (with rtmp) library with PIE for Android 5.0 compatibility.

  The library works fine without -pie, but when I try to recompile it with the following flags :

  LOCAL_CFLAGS += -fPIE
  
  LOCAL_LDFLAGS += -fPIE -pie

  the following error gets thrown :

  /Users/lgorse/Android_Libraries/android-ndk-r10e/platforms/android-21/arch-arm/usr/lib/crtbegin_dynamic.o:crtbrand.c:function _start: error: undefined reference to 'main'
  
  Error:error: ld returned 1 exit status
  
  make: *** [obj/local/armeabi/libffmpegbridge.so] Error 1
  
  make: Leaving directory `/Users/lgorse/Android_Libraries/ffmpegbridge/app/src/main'
  
  :app:ndkBuild FAILED
  
  Error:Execution failed for task ':app:ndkBuild'.
  
  > Process 'command '/Users/lgorse/Android_Libraries/android-ndk-r10e/ndk-build'' finished with non-zero exit value 2

  It seems that the ndk-build is trying to access a .main method from within crtbegin_dynamic. Those files are built-in with the NDK so I assume there’s nothing fundamentally wrong with them, and I’m attempting to run my configuration in the wrong way.

  Here is the Android.mk file :

  LOCAL_PATH := $(call my-dir)
  
  
  
  include $(CLEAR_VARS)
  
  
  
  LOCAL_MODULE := ffmpegbridge
  
  LOCAL_SRC_FILES := ffmpegbridge.c ffmpegbridge_context.c logdump.c
  
  LOCAL_CFLAGS := -I$(LOCAL_PATH)/include -I$(LOCAL_PATH)/../prebuilt/include
  
  LOCAL_CFLAGS += -fPIE
  
  LOCAL_LDFLAGS += -fPIE -pie
  
  LOCAL_LDLIBS += -llog
  
  LOCAL_LDLIBS += -L$(LOCAL_PATH)/../prebuilt/lib
  
  LOCAL_LDLIBS += -lcrypto -lssl -lrtmp-1 -lavcodec-56 -lavdevice-56 -lavfilter-5 -lavformat-56 -lavutil-54 -lswresample-1 -lswscale-3
  
  
  
  include $(BUILD_SHARED_LIBRARY)

  Here is my Gradle file (it contains the build instructions for ndkBuild) :

  apply plugin: 'android'
  
  
  
  android {
  
      compileSdkVersion 19
  
      buildToolsVersion "19.1.0"
  
  
  
      defaultConfig {
  
          applicationId "io.cine.ffmpegbridge"
  
          minSdkVersion 18
  
          targetSdkVersion 19
  
          versionCode 1
  
          versionName "1.0"
  
      }
  
  
  
      buildTypes {
  
          release {
  
              minifyEnabled false
  
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
  
          }
  
      }
  
      sourceSets.main {
  
          jniLibs.srcDir 'src/main/libs'
  
          jni.srcDirs = [] // disable NDK-auto-build
  
      }
  
  
  
      Properties properties = new Properties()
  
      properties.load(project.rootProject.file('local.properties').newDataInputStream())
  
  
  
      task ndkBuild(type: Exec) {
  
          def ndkDir = properties.getProperty('ndk.dir')
  
          commandLine "$ndkDir/ndk-build", '-C', file('src/main').absolutePath
  
      }
  
  
  
      task cleanNdkBuild(type: Exec) {
  
          def ndkDir = properties.getProperty('ndk.dir')
  
          commandLine "$ndkDir/ndk-build", '-C', file('src/main').absolutePath, "clean"
  
      }
  
  
  
      tasks.withType(JavaCompile) { compileTask -> compileTask.dependsOn ndkBuild }
  
      clean.dependsOn cleanNdkBuild
  
  }
  
  
  
  dependencies {
  
      compile fileTree(dir: 'libs', include: ['*.jar'])
  
  }

  I’ll be watching this question closely so feel free to ask for follow-ups. I’m definitely around !

• Slowing down 960 fps video with ffmpeg (setpts is not working)

  7 novembre 2016, par haridsv

  I am trying to slow down a video recorded on an Android phone at 960fps. I found a lot of previous posts and blogs that all basically say the same thing, that you need to change the "presentation timestamp" (pts). I also found the official documentation that is saying the same thing. The command-line basically looks like this :

  ffmpeg -i input.mp4 -filter:v "setpts=4*PTS" -r 30 -y output.mp4

  I copied the video file using Android Filter Transfer and when I use the above command-line, it works to slow it down, but the resulting output is choppy. The output of the ffmpeg also indicates that it is duplicating the frames :

  frame=  687 fps=103 q=-1.0 Lsize=    4454kB time=00:00:22.80 bitrate=1600.1kbits/s dup=515 drop=0 speed=3.42x

  Running ffprobe on the file shows this :

  ffprobe version 3.1.1 Copyright (c) 2007-2016 the FFmpeg developers
  
    built with Apple LLVM version 7.3.0 (clang-703.0.31)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/3.1.1 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-lda
  
    libavutil      55. 28.100 / 55. 28.100
  
    libavcodec     57. 48.101 / 57. 48.101
  
    libavformat    57. 41.100 / 57. 41.100
  
    libavdevice    57.  0.101 / 57.  0.101
  
    libavfilter     6. 47.100 /  6. 47.100
  
    libavresample   3.  0.  0 /  3.  0.  0
  
    libswscale      4.  1.100 /  4.  1.100
  
    libswresample   2.  1.100 /  2.  1.100
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'VID_20161030_213810.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: isommp42
  
      creation_time   : 2016-10-30 16:08:14
  
      location        : +17.3874+078.3395/
  
      location-eng    : +17.3874+078.3395/
  
      com.android.version: 6.0.1
  
      com.android.capture.fps: 120.000000
  
    Duration: 00:00:05.73, start: 0.000000, bitrate: 14991 kb/s
  
      Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720, 13859 kb/s, SAR 1:1 DAR 16:9, 30 fps, 30 tbr, 90k tbn, 180k tbc (default)
  
      Metadata:
  
        creation_time   : 2016-10-30 16:08:14
  
        handler_name    : VideoHandle

  This seems to detect that the video is 30 fps instead of 960 fps, which is probably why it is filling in with duplicate frames instead of using the existing frames.

  I recording the video on Lenovo Z2 Plus (AKA Zuk Z2). If I playback the video using the built-in player at a slow speed it looks extremely smooth, so the frames are definitely there. Could someone help me figure out the right way ? The file is available here (about 10MB), in case someone would like to try it.

  Update : Video playback at slo-mo on the phone recorded with another phone. Notice how smooth and slow the sparks are thrown around, which is impossible if the original video is 30fps.

  • Slow-mo clip 1
  • Slow-mo click 2
  • Full video played in slow-mo (47s, probably at 120fps)