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• Converting png images series to webm with transparent white background from Daz3d

  25 août 2015, par James

  I’m trying to make a webm video with a transparent background from a Daz3D model.
  My process is export png image series with transparent background from Daz3D, use ffmpeg to convert png series to webm video.
  This was working well in Daz3D 4.6.

  But in Daz3D 4.8 the exported background is black instead of white, so when converted to webm is ok on Chrome as has the transparency, but on Firefox is black and has a halo (as Firefox does not support transparency so displays background).

  So I’m looking for a solution with Daz3D, or tools like ImageMagik.
  I almost got it with ImageMagik,

  convert -alpha extract *.png mask.png
  
  mogrify -flatten talk*.png
  
  for /f %x in ('dir /s /b blink*.png') do @composite -compose CopyOpacity mask-0.png %x %x

  But for some reason the final webm has a white background not transparent ...
  Some more info here,

  http://www.daz3d.com/forums/discussion/61237/daz3d-4-8-png-background-is-black

  and here,

  http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=28214

  >
  Doh, okay I figured it out. My images were good, but I somehow have two different versions of ffmpeg on my computer and was using the wrong one that doesn’t seem to support transparency.

  Now it is working.

  My only issue is the last shell line,

  for /f %x in (’dir /s /b blink*.png’) do @composite -compose CopyOpacity mask-0.png %x %x

  This only uses mask-0.png, instead of mask-1 for blink01.png, mask-2 for blink02.png etc.

• How to set specific minimal bitrate of video with light_compressor package in Flutter ?

  21 juin 2023, par Giant Brain

  I tried using flutter's light_compressor package to compress a video I shot with my phone or downloaded from YouTube.

  


  I refer to the article below.
https://morioh.com/p/ac6f0d2c176b
In this article, the minimum bit rate can be set and the default value is 2mbps.

  


  However, in the sample code, only the flag isMinBitrateCheckEnabled exists, and there is no parameter to set a specific bit rate.

  


  How do I compress the video to my desired bitrate ?

  


  Below is a part of the sample code.

  


  import 'package:light_compressor/light_compressor.dart';


final LightCompressor _lightCompressor = LightCompressor();
final dynamic response = await _lightCompressor.compressVideo(
  path: _sourcePath,
  destinationPath: _destinationPath,
  videoQuality: VideoQuality.medium,
  isMinBitrateCheckEnabled: false,
  frameRate: 24 /* or ignore it */);


  


• FFMPEG extract frame-accurate video fragments with minimal transcoding

  9 mars 2018, par Leeroy

  How can I extract frame-accurate video or audio fragments using FFMPEG without transcoding the full portion ?

  ffmpeg -i input.mp4 -ss 00:00:01.234 -to 00:00:05.678 output.mp4 works because it re-encodes... If I use -codec: copy then it disregards the precision of my start and end time arguments and instead uses the closest keyframe (I understand).

  Is there a command or combination of commands to instruct FFMPEG to transcode only what’s needed, the bits near the start/end markers, up to keyframes ?

  EDIT : A bit of context... I’m trying to write this function to process video piped from youtube-dl, perhaps even as a service. So it matters that I minimize bandwidth (downloading to timestamp and discarding after) and CPU utilization (re-encoding all of the fragment).