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• 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.

• Convert video file to TIFF with ffmpeg.dll or avcodec.dll ? Is "on-the-fly" possible ?

  27 octobre 2011, par Berschi

  I want to create a program, which gets a video-file from Qt, converts that video file to TIFF-files and sends them to an algorithm which handles these TIFF-Files.
  My questions :

  • is it possible with ffmpeg or avcodec not to convert a video-file to TIFF-files first on harddrive and send them to the algorithm after that, but to convert frame for frame and send it to the algorithm right away ?
  • The more important question : Is it possible to do that not with an external process with ffmpeg.exe, but with ffmpeg.dll ? Or is it only possible with avcodec.dll ? (It doesn't have to be "on-the-fly" like at my point above) How can I create a ffmpeg.dll with header and lib ?

• How many key frames have been encoded in my video ? ffmpeg was the encoder used

  3 janvier 2012, par user1127753

  I am attempting to add a keyframe every second using "-g 25" as an option with ffmpeg.

  I need a way however, to query the output video, and other videos on my server to see how many keyframes have been encoded.

  Is there an ffmpeg command line attribute which will tell me this information ? Or any other tool ? Please help !