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• lavf/ftp: check for truncation in snprintf

  25 novembre 2021, par Anton Khirnov

  lavf/ftp: check for truncation in snprintf
  Silences e.g. the following warning in gcc 10 :
  
  src/libavformat/ftp.c : In function ‘ftp_move’ :
  
  src/libavformat/ftp.c:1122:46 : warning : ‘%s’ directive output may be truncated writing up to 4095 bytes into a region of size 4091 [-Wformat-truncation=]
  
   1122 |     snprintf(command, sizeof(command), "RNTO %s\r\n", path) ;
  
        |                                              ^  
  
  src/libavformat/ftp.c:1122:5 : note : ‘snprintf’ output between 8 and 4103 bytes into a destination of size 4096
  
   1122 |     snprintf(command, sizeof(command), "RNTO %s\r\n", path) ;
  
        |     ^ 
  

  • [DH] libavformat/ftp.c

• How to create movie screenshot by ffmpeg in an amazon S3 path

  5 décembre 2019, par user2004082

  I tried to create using ffmpeg a video screenshot from a remote video url in heroku console. Below is how I generated a movie instance and can see also an empty ready to be written file at S3. But the last line movie.screenshot is not working and generates this error :

  FFMPEG::Error: Failed encoding.Errors: no output file created

  Here is the code

  s3 = Aws::S3::Resource.new(region: 'us-west-1')
  
  bucket = s3.bucket("ruby-sample-kb-#{SecureRandom.uuid}")
  
  bucket.create
  
  object = bucket.object('ex-vid-test-kb.jpg')
  
  object.put(acl: "public-read-write")
  
  path = object.public_url
  
  movie = FFMPEG::Movie.new("https://www.googleapis.com/download/storage/v1/b/seppoav/o/3606137_51447286560__56BAF29C-05CB-4223-BAE6-655DF2236321.MOV?generation=1492780072394755&alt=media")
  
  movie.screenshot(path, :seek_time => 2)

  I also tried the following line just if it should be written via put. What am I missing here ?

  object.put(acl: "public-read", body: movie.screenshot(path, :seek_time => 2))

• advanced ffmpeg compression control

  18 juillet 2017, par Daniel Mahler

  I am using very aggressive video compression, eg -crf 51. I am using this for ’artistic’ effect, so what I am doing may not make sense from a normal video compression point of view.

  So far I have only been using very basic compression control using only the -crf or -b:v flags. The results look like ffmpeg divides images into square patches and the makes smooth approximations within the patches. This gives 2 control dimensions to the process : the patch size and the aggressiveness of the smoothing within the patches.

  It have found that ffmpeg uses both parameters to some extent, but there appears to be an absolute maximum patch size in pixels beyond which it will not go regardless of the frame size.
  After that it will only increase compression by reducing the detail within the patches.

  This is suboptimal for high resolution video, where this becomes equivalent to reducing the resolution. The problem is particularly noticeable on fractal like images which have large featureless region as well as regions of high detail.

  How can I tell ffmpeg to increase the maximum patch size and retain more detail within the patches ?