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• FFMPEG Replacing black color fragments with alpha channel transparency

  31 décembre 2017, par kostya572

  I have file.mov video. It has a lot of blank black color fragments that have different durations.

  I need to replace black color fragments that show up for more than 5 seconds with transparency. Is that possible to add some alpha channel for that purpose ?

  Comment to Mulvya’s answer :

  Amazing solution. With #2 section everything ok.

  With #1 section I created this code :

  output=$(ffprobe -f lavfi -i "movie=file.mov,blackdetect=d=3.5" -show_entries tags=lavfi.black_start,lavfi.black_end -of compact=p=0 -v 0|awk '!/^$/')
  
  echo $output

  using awk '!/^$/' to remove empty lines.

  Here is the output I get :

  

  tag:lavfi.black_start repeats with same value several times, not having right structure with closing tag:lavfi.black_end

  If I change blackdetect=d=3.5 to other value, for exaple d=10, it outputs the same result as d=3.5. How could I solve this issue having right tag:lavfi.black_start,tag:lavfi.black_end synthax with correct grepping d= value ?

• Overlaying one video on another one and making black pixels or green pixels transparent

  30 décembre 2017, par kostya572

  I found great answer here : https://stackoverflow.com/a/38581696/2337706

  It works only for black pixels. The result is not perfect. I guess if change the overlay background color to other color, e.g. green, red, blue the results would be better. How can I change the other background color ?

  Here is my working code :

  ffmpeg -y \
  
      -i video.webm -i overlay.mov \
  
      -filter_complex " \
  
          [0:v]setpts=PTS-STARTPTS[base]; \
  
          [1:v]crop=iw:0.50*ih,setpts=PTS-STARTPTS+0/TB, \
  
                   format=yuva420p,colorchannelmixer=aa=0.7[overlay]; \
  
       [base][overlay]overlay=x=(W-w)/2:y=0[v]" \
  
   -map "[v]" -map 0:a -c:a copy -c:v libvpx-vp9 -lossless 1 -threads 4 -quality realtime \
  
   -speed 8 -tile-columns 6 -frame-parallel 1 -vsync 2 -shortest output.webm

  The result :
  

  Need result :
  

  Or need result (if impossible first with good quality) :
  

  Thank you, sorry for the frequent questions on ffpmpeg topic.

• Cut AVI video via FFMPEG results in black screen video, but audio is OK

  25 décembre 2017, par mipi

  I want to trim a AVI video (H264 codec) via ffmpeg. The time interval for the result is available as START_TIME_ORIG and DURATION_ORIG (both in microseconds). To make sure that the resulting video starts with an IDR frame, I determine START_TIME and DURATION via ffprobe by executing

  ffprobe -show_frames -pretty -read_intervals [TIME_FROM%TIME_TO] input.avi

  twice to get the IDR frames which are (1st call) closest to START_TIME_ORIG and (2nd call) closest to START_TIME_ORIG+DURATION_ORIG. TIME_FROM and TIME_TO is an interval of 5 seconds plus/minus around (1st call) START_TIME_ORIG and (2nd call) START_TIME_ORIG+DURATION_ORIG. To identify a frame as IDR frame I verify that key_frame=1 and pict_type=I. START_TIME is then set to pkt_dts_time of that frame. In a similar way I calculate DURATION.

  Then ffmpeg is called :

  ffmpeg -ss [START_TIME] -i input.avi -t [DURATION] -codec copy -reset_timestamps 1 -async 1 -map 0 -y output.avi

  Unfortunately the resulting video has a black screen only, audio is OK. What is wrong with my approach ?
  Thanks, mipi