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• FFMPEG code is not trimming the videos properly

  8 mai 2022, par michaelmuller20

  I am trying to trim videos from a specific folder using ffmpeg via powershell but it seems the out doesn't work. However, the files are being renamed as per the code.

  


  <# 

This script trims videos with ffmpeg using a start and end time.
Code below that calls ffmpeg and ffprobe assumes those executables 
are included in the return for $env:path. If this is not the 
case, either add them to PATH or call the .exe using the full
path.

#>

    $files = Get-ChildItem -Filter "*.mp4" -LiteralPath "C:\Users\PC\Desktop\Sample" # create a list of files to process
    $bool_fast = $true # use a fast method to trim the video file. Set to $false to use the slow method.

    ForEach ($f in $files) {
        # set up file names
        $src = $dest = $f.FullName # store original file name
        $new_name = "$($f.BaseName)_LONGER$($f.Extension)" # create a new file name for original file by inserting "_LONGER" before the extension
        Rename-Item -Path $src -NewName $new_name # rename the original file so we can use its name for the output (ffmpeg can't overwrite files)
        $src = $dest.Replace($f.Name, $new_name) # store the new source file name

        # get the file length in seconds
        $strcmd = "ffprobe -v quiet -print_format compact=print_section=0:nokey=1:escape=csv -show_entries format=duration $src" # outputs seconds
        $len = Invoke-Expression $strcmd

        # set start and end times
        $start = 0 # where to start trim in seconds from the beginnning of original video
        $end = 4 # where to end trim in seconds from the beginnning of original video

        # trim the video
        If ($bool_fast) {
            # this method seeks to the nearest i-frame and copies ... fast
            $strcmd = "ffmpeg -i $src -ss $start -to $end -c:v copy -c:a copy $dest"
        } Else {
            # this method re-encodes the file ... slow, but more accurate adherence to a time specification
            $strcmd = "ffmpeg -i $src -ss $start -to $end $dest"
        }
        Invoke-Expression $strcmd
    }


  


• avformat/mov : Add support for still image AVIF parsing

  22 avril 2022, par Vignesh Venkatasubramanian

  avformat/mov : Add support for still image AVIF parsing
  This patch supports AVIF still images conforming to the
  
  final specification that have exactly one item (i.e. no alpha channel).
  
  The iloc box is parsed and the mov index populated.
  Partially fixes #7621.
  Signed-off-by : Vignesh Venkatasubramanian <vigneshv@google.com>
  
  Signed-off-by : Gyan Doshi <ffmpeg@gyani.pro>
  

  • [DH] libavformat/isom.h
  • [DH] libavformat/mov.c

• FFmpeg cant recognize 3 channels with each 32 bit

  4 avril 2022, par Chryfi

  I am writing the linearized depth buffer of a game to openEXR using FFmpeg. Unfortunately, FFmpeg does not adhere to the openEXR file specification fully (like allowing unsigned integer for one channel) so I am writing one float channel to openEXR, which is put into the green channel with this command -f rawvideo -pix_fmt grayf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr.

  


  The float range is from 0F to 1F and it is linear. I can confirm that the calculation and linearization is correct by testing 16 bit integer (per pixel component) PNG in Blender compositor. The 16 bit integer data is written like this short s = (short) (linearzieDepth(depth) * (Math.pow(2,16) - 1)) whereas for float the linearized value is directly written to OpenEXR without multiplying with a value.

  


  However, when viewing the openEXR file it doesn't have the same "gradient" as the 16 bit png... when viewing them side by side, it appears as if the values near 0 are not linear, and they are not as dark as they should be like in the 16 bit png.
(And yes, I set the image node to linear), and comparing it with 3d tracking data from the game I cant reproduce the depth and cant mask things using the depth buffer where as with the png I can.

  


  How is it possible for a linear float range to turn out so different to a linear integer range in an image ?

  


  UPDATE :

  


  I now write 3 channels to the ffmpeg with this code

  


  float f2 = this.linearizeDepth(depth);

buffer.putFloat(f2);
buffer.putFloat(0);
buffer.putFloat(0);


  


  the byte buffer is of the size width * height * 3 * 4 -> 3 channels with each 4 bytes. The command is now -f rawvideo -pix_fmt gbrpf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr which should mean that the input (byte buffer) is expecting 32 bit floats with 3 channels.

  


  FFmpeg is somehow splitting up channels or whatever... could be a bug, could be my fault ?