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• How can I add a background image while combining *.png files using ffmpeg

  12 février 2023, par Walt Howard

  I'd like to add a background image while combining *.png files to make an mp4 file, using ffmpeg.

  


  Currently, I have to first create an animated gif using imagemagick convert, like this :

  


  convert -delay ${DELAY} -dispose Background *.png -coalesce null: ${BACKGROUND} -compose dstOver -layers composite -layers optimize -loop 0 planet.gif


  


  Then I process that animated gif using ffmpeg to optimize it :

  


  ffmpeg -i planet.gif -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" planet.mp4


  


  Which sort of works, but is slow and has a problem. I craps out if I go above about 100 input files, and creates animated gifs that are basically just white screens.

  


  ffmpeg alone works great, and 100 times faster stitching the *.png files together

  


  ffmpeg -framerate 10 -pattern_type glob -i '*.png' -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" planet.mp4

  


  But, no background there. I haven't found anyway to add that background. Does ffmpeg even support such a thing ?

  


• ffmpeg : How does one designate what parts of an overlay video stream let the underlay video stream show through ?

  21 février 2023, par Walt Howard

  Stream 0 is a rotating planet created using povray. (https://www.povray.org/)

  


  Stream 1 is just a static jpeg of stars.

  


  I'm using overlay like this :

  


  nice ffmpeg -i protoplanet.mp4 -i stars.jpg \
         -filter_complex "[0:v]scale=1024:768[scaled];[1:v][scaled]overlay=0:0" \
         -movflags faststart -pix_fmt yuv420p -r 10 planet.mp4


  


  I had it working when I used the output from povray directly. I didn't have to know why that worked, because it just did. However, after adding some post processing to the planet video, the entire video has no alpha channel (educated guess) so the background stream (Stream 1) cannot show through.

  


  The post processing I did was this (which works great) : https://www.reddit.com/r/ffmpeg/comments/im2mkp/creating_a_retro_glow_effect_with_ffmpeg/

  


  But that made the video unable to have an overlay background possibly due to it destroying the alpha channel and turning many of the blacks to dark grey.

  


  I can merge the pure POVRAY output and the background and then add the glow effect, but it adds the effect to the background stars and captions also which ruins the effect to some degree. I want to glo-ify the planet first, then stick it on a pure starfield background.

  


  In thinking this over I may have to recreate the alpha channel after adding the glow effect, using a nearest match to black and dark grey to alpha.

  


  Hmmm. It might be a codec issue as I didn't specify any -c:v in any of my commands....

  


• FFMpeg on Android, undefined references to libavcodec functions, although it is listed on command line

  24 mars 2019, par dimsuz

  I have a problem with unresolved references to ffmpeg’s libavcodec functions, so far failed to find the answer in other places (including my mind) :)

  Let me describe my setup - it takes space, but is really basic, it might be that I’m failing to see some error...

  I built an FFMPeg with ndk r5 toolchain, ffmpeg port I got from http://bambuser.com/opensource (as recommended in other questions here). It built fine, so I put several static libraries in my project like this :

  <project>/jni/bambuser_ffmpeg/libavcodec.a
  
  <project>/jni/bambuser_ffmpeg/libavformat.a
  
  <project>/jni/bambuser_ffmpeg/libavcore.a
  
  <project>/jni/bambuser_ffmpeg/libavutil.a
  
  </project></project></project></project>

  Next, I created an Android.mk in bambuser_ffmpeg folder to list these libs as a prebuilt ones :

  LOCAL_PATH := $(call my-dir)
  
  
  
  include $(CLEAR_VARS)
  
  LOCAL_MODULE := bambuser-libavcore
  
  LOCAL_SRC_FILES := libavcore.a
  
  include $(PREBUILT_STATIC_LIBRARY)
  
  
  
  include $(CLEAR_VARS)
  
  LOCAL_MODULE := bambuser-libavformat
  
  LOCAL_SRC_FILES := libavformat.a
  
  include $(PREBUILT_STATIC_LIBRARY)
  
  
  
  (same for other two libs)

  Next, I have another module which references these libs in its Android.mk, sets up include paths, etc :

  LOCAL_PATH := $(call my-dir)
  
  
  
  include $(CLEAR_VARS)
  
  
  
  LOCAL_MODULE := ffmpegtest
  
  LOCAL_STATIC_LIBRARIES := bambuser-libavcodec bambuser-libavcore bambuser-libavformat bambuser-libavutil
  
  LOCAL_SRC_FILES := ffmpeg_test.cpp
  
  LOCAL_C_INCLUDES := $(LOCAL_PATH)/../bambuser_ffmpeg/include
  
  LOCAL_LDLIBS    := -llog -lz
  
  
  
  include $(BUILD_SHARED_LIBRARY)

  And finally I have my ffmpeg_test.cpp which is really basic, like this :

  #include 
  
  
  
  extern "C" {
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  }
  
  
  
  extern "C" {
  
      JNIEXPORT jint JNICALL Java_com_the7art_ffmpegtest_PaintThread_testFFMpeg(JNIEnv* env, jobject obj, jstring fileName);
  
  }
  
  
  
  JNIEXPORT jint JNICALL Java_com_the7art_ffmpegtest_PaintThread_testFFMpeg(JNIEnv* env, jobject obj, jstring fileName)
  
  {
  
      av_register_all();
  
      return 0;
  
  }

  When I run ndk-build, it compiles fine, but when linking it prints an unresolved reference to almost every function in libavcodec. Looks like only this lib’s functions are failing to be located :

  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(allformats.o): In function `av_register_all':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/allformats.c:47: undefined reference to `avcodec_register_all'
  
  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(utils.o): In function `parse_frame_rate':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:3240: undefined reference to `av_parse_video_rate'
  
  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(utils.o): In function `parse_image_size':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:3234: undefined reference to `av_parse_video_size'
  
  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(utils.o): In function `flush_packet_queue':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:1277: undefined reference to `av_free_packet'
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:1283: undefined reference to `av_free_packet'
  
  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(utils.o): In function `get_audio_frame_size':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:766: undefined reference to `av_get_bits_per_sample'
  
  /home/dimka/src/mobile/android/ffmpegtest/obj/local/armeabi/libavformat.a(utils.o): In function `ff_interleave_add_packet':
  
  /home/dimka/work/suzy/tmp/ffmpeg-android/ffmpeg/libavformat/utils.c:2909: undefined reference to `av_dup_packet'
  
  and so on...

  I fail to figure why this is happening. I tried running ndk-build V=1 to check the actual linking command, and libavcodec is sitting there perfectly right, like it should. All other ffmpeg libs are there too.

  Any hints ?