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• Use ffmpeg to compile RGBA image sequence into two separate videos (RGB + Alpha)

  27 novembre 2018, par MirceaKitsune

  I plan on using Blender to render animated sequences for a game. I need the videos to have transparent backgrounds in the format expected by its engine. This format involves the transparency being defined as a separate grayscale video of equal FPS and duration. Since splitting the RGB and Alpha channels in Blender is more complicated, I’d prefer doing this directly from ffmpeg.

  The input directory contains an image sequence of png files in RGBA format (eg : 0000.png to 0100.png). What I need ffmpeg to do is compile them into two separate videos : One containing only the RGB channels (leave transparency black) and another containing only the grayscale alpha channel. In the end I’d have something like my_video.mp4 + my_video_mask.mp4.

  I’m familiar with compiling non-transparent image sequences into video using :

  ffmpeg -f image2 -i /path/to/sequence/%04d.png output.mp4

  But I don’t know how to extract the alpha channel and make it a separate video file. What is the simplest ffmpeg command to achieve this result ?

• Windows ffmpeg batch to find folder containing VOBs, concatenate and convert, move to next folder [on hold]

  27 novembre 2018, par Daniel Cooper

  All,

  I am in need of help that is beyond my capabilities. I need to run a batch command in Windows that finds VOB files in a folder, concatenates and converts them using ffmpeg, and then continues the recursive search for more folders containing VOBs.

  The idea is that the cmd file would be copied into the root that the command should look under when running. I have found commands that find VOBs and I have found ffmpeg scripts that concatenate and convert, but combining these functionalities together in the way I need is proving above my level.

  Thank you all in advance.

  EDIT :
  The computer I am running this code on is off the network so I had to manually retype. Any typo’s here are therefore likely from the retyping since the codes seem to function as intended originally...

  This code creates a list of folders that contain VTS*.VOB (as opposed to just all *.VOBs because that would include a certain useless VOB that is present in each folder).

  for /r %%a in (.) do @if exist "%%~fa\VTS*.VOB" echo %%~fa >> folderlist.txt

  This piece combines VTS*.VOBs and then converts them to MP4

  @ECHO OFF
  
  md ffmpeg_output
  
  for %%f in (VTS*.VOB) do echo file '%%f' >> filelist.txt
  
  ffmpeg -f concat -i filelist.txt -c copy "ffmpeg_output\Total.VOB"
  
  ffmpeg -i "ffmpeg_output\Total.VOB" -c:v libx264 -pix_fmt yuv420p -c:a copy "ffmpeg_output\Converted.mp4"

  I attempted to essentially nest the for loops with the idea that the first snippet above would produce a txt file, which I could then "for /f" through each line to direct the second snippet of code for concatenation and conversion of the VOB files. However this plan never got off the ground as I am unable to figure out the viability or syntax of nesting for loops in this way.

• Is it possible to use FFmpeg to cut "random" sections from a folder of videos and concat them into 1 video ?

  14 novembre 2018, par EmmyStrand

  I realize this sounds like an easy question, and one that has been answered before. However, I cannot seem to find a script which can read a folder of videos with varying lengths, copy a random segment from each video, and concat them into a single video.

  An example :

  I have a folder with 150 videos labeled Fashion-Setlist-01.mp4, Fashion-Setlist-02.mp4, etc.
  Each are over 1 hour. I would like to pull a random 10 seconds section from each video and then randomly add them together resulting in a video. This may seem easy with only a few videos, but the plan is to read from potentially 100’s of videos. It should be possible to pull multiple sections from each video as well. I suppose we could run the script twice for more segments if the video needed to be longer.