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• Using ffmpeg to capture frames at intervals from a video

  25 octobre 2011, par TheShaggyBeard

  So here is what I am trying to do - I want to automate creating animated gif previews from a video file (in this case I know they will always be a specific format). Here is what I have :

  echo 'Make a folder named "filenamemp4"'
  
  folderName=$(find . -type f -name "*.mp4" | grep -o [[:alnum:]] | tr -d '\n' | cat)
  
  
  
  echo 'Grab the frame rate and total number of frames and put them into xaa and xab'
  
  qtinfo asa.mp4 | awk 'NR = 1 { print $2 }' | grep -o "^[0-9]*" | split -l 1
  
  
  
  echo 'Assign values to variable'
  
  frameRate=$(cat xaa)
  
  frameTotal=$(cat xab)
  
  videoLength=$(expr $frameTotal / $frameRate)
  
  
  
  echo 'Take a screenshot at 10% intervals - this is the part that gives me a bitrate error.  It says that the -r option has an invalid input being 1 / value of videoLength' 
  
  ffmpeg -i asa.mp4 -y -ss $videoLength -an -sameq -f image2 -s 'qcif' -r $(expr 1/$videoLength) preview%02d.jpg
  
  
  
  echo 'Take the jpgs and mash them into an animated gif'
  
  convert -delay 50 -loop 10 preview*.jpg preview.gif
  
  
  
  echo 'Move the gif to the specified folder'
  
  mv preview.gif $folderName/preview.gif
  
  
  
  echo 'Clean Up'
  
  find . -type f -name "*.jpg" -exec rm -rf {} \;

  So perhaps there is a better way of doing this, or I am understanding how to use the -r option of ffmpeg wrong. In the tutorial I read on ffmpeg for a similar scenario, they used -r 1/5 to produce frames with a 5 second interval. My assumption is that for the desired interval you want, you just slap it in the denominator for the -r option.

• ffmpeg h.264 video plays in Safari but not in Chrome

  6 mars 2016, par ensnare

  I’m using ffmpeg to encode a .MOV raw video into a compressed H.264 video for display on an html5 website. I’m using the below string to encode the video :

  ffmpeg -y \
  
  -i in.mov
  
  -b 3500k -bt 4000k \
  
  -acodec libfaac -ac 2 -ar 48000 -ab 192k \
  
  -vcodec libx264 -vpre ultrafast -vpre baseline \
  
  out.mp4

  The resulting video looks great and plays fine in Safari, but Chrome can’t recognize it. Any ideas ?

  Thanks.

• ffmpeg bitrate error when trying to capture frames at intervals from a video

  25 octobre 2011, par TheShaggyBeard

  Here is the error I get from running this script :

  [mjpeg @ 0x8559710]bitrate tolerance too small for bitrate
  Error while opening codec for output stream #0.0 - maybe incorrect parameters such as bit_rate, rate, width or height

  So here is what I am trying to do - I want to automate creating animated gif previews from a video file (in this case I know they will always be a specific format being mp4). Here is what I have :

  echo 'Save the file-name and make a folder named "filenamemp4"'
  
  fileName=$(find . -type f -name "*.mp4")
  
  folderName=$( cat $fileName | grep -o [[:alnum:]] | tr -d '\n' | cat)
  
  
  
  echo 'Grab the frame rate and total number of frames and put them into xaa and xab'
  
  qtinfo asa.mp4 | awk 'NR = 1 { print $2 }' | grep -o "^[0-9]*" | split -l 1
  
  
  
  echo 'Assign values to variable'
  
  frameRate=$(cat xaa)
  
  frameTotal=$(cat xab)
  
  videoLength=$(expr $frameTotal / $frameRate)
  
  
  
  echo 'Take a screenshot at 10% intervals - this is the part that gives me a bitrate error.  It says that the -r option has an invalid input being 1 / value of videoLength' 
  
  ffmpeg -i $fileName -y -ss $videoLength -an -sameq -f image2 -s 'qcif' -r $(expr 1/$videoLength) preview%02d.jpg
  
  
  
  echo 'Take the jpgs and mash them into an animated gif'
  
  convert -delay 50 -loop 10 preview*.jpg preview.gif
  
  
  
  echo 'Move the gif to the specified folder'
  
  mv preview.gif $folderName/preview.gif
  
  
  
  echo 'Clean Up'
  
  find . -type f -name "*.jpg" -exec rm -rf {} \;

  So perhaps there is a better way of doing this, or I am understanding how to use the -r option of ffmpeg wrong. In the tutorial I read on ffmpeg for a similar scenario, they used -r 1/5 to produce frames with a 5 second interval. My assumption is that for the desired interval you want, you just slap it in the denominator for the -r option.