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• FFMPEG-WEBM : Issue with premultiplied alphas WebM

  17 septembre 2017, par Blake Buell

  I rendered a transparent Mov with a semi-transparent logo on it in Vegas Pro 15 and I converted that to a WebM using FFmpeg so I can put it on my website. When I looked at the logo with the WebM in chrome it had this gray tint compared to the original that was a lot brighter. I’m having a feeling this has something to do with premultiplied alphas but I don’t know how to deal with this with a WebM on chrome.
  I think I would need to convert the premultiplied alpha to a straight alpha and if so how would I do this with FFmpeg ?

  Here is the command I used to convert to WebM if this is useful.

  ffmpeg -i temp/Digi-Logo.mov -c:v libvpx -b:v 2000k -cpu-used 2 -pix_fmt yuva420p -auto-alt-ref 0 -deadline 600 logo/1.webm

  Original :
  

  Converted :
  

  EDIT : My guess is that FFmpeg when converting the MOV to WebM it removes the premultiplied alpha channel data and makes it that gray color. How would I make it so FFmpeg converts the transparent MOV to WebM and keeps the premultiplied alpha channel.

• Using hwaccel ffmpeg option with moviepy library

  12 octobre 2022, par Nicola Lepetit

  I am trying to add the hwaccel option of ffmpeg to a script I am working on in Python, based on the moviepy library, by passing the options via the ffmpeg_params parameter :

  


  from moviepy.editor import VideoFileClip

ASSETS_FOLDER = "./assets/backgrounds/road/"
video_file_name = "12386.mp4"
start_time = 5
end_time = 20
target_file = "output.mp4"

video = VideoFileClip(f"{ASSETS_FOLDER}{video_file_name}")
new = video.subclip(start_time, end_time)
new.fps = 25
new.write_videofile(target_file, ffmpeg_params= ['-hwaccel','cuda'])


  


  The problem is that these ffmpeg_params are added at the end of the ffmpeg command line, so I am getting the following error :

  


  [Errno 22] Invalid argument

MoviePy error: FFMPEG encountered the following error while writing file 
   ./assets/temp/3/cut1.mp4:

 b'Option hwaccel (use HW accelerated decoding) cannot be applied to output url 
  ./assets/temp/3/cut1.mp4 -- you are trying to apply an input option to an output file
  or vice versa. Move this option before the file it belongs to.\r\nError parsing
  options for output file ./assets/temp/3/cut1.mp4.\r\nError opening output files:
  Invalid argument\r\n'


  


  Is there another way to use the option with moviepy

  


• ffmpeg : improving MP4 to webm ogg conversions

  14 juillet 2017, par Randy

  (Edited to include some of the things I’ve tried)

  I’m a musician, and occasional web coder. I’ve been using video editing software (old version of Roxio Videowave from 2011) to build promotional videos from clips of some of my performances, and I’d like to put some of them on my own web pages in HTML5 video format. So that currently means I need MP4, WEBM, and OGG conversions. Fortunately the editing software churns out some very nice MP4 (H264) files, and has plenty of options for doing so. I purposely output the output size about 2X the likely display size, in hopes of offering more detail for better conversions. Specifically, the video output was AVC/H.264, 800 x 450, 30fps, variable bit rate, but with 600000 as a base line (that was the default for this setting anyway).

  Now I’m nowhere near expert at this stuff, and I probably left out some important data. But bottom line, the resulting MP4 looked very good. Unfortunately, to put it on my own web page means at least converting to WEBM and OGG formats. It would be nice if all browsers just supported MP4, but then there would be licensing fees, so conversions are needed. Sadly, I’ve been wasting days now trying to do this with ffmpeg. Its easy to do, its doing it WELL that is a mystery to me. Just letting ffmpeg work using its defaults (meaning I just specify an input and output file) results in pretty terrible video. But I’ve also tried most of the settings for better quality available, and the resulting conversions are nowhere near as good as youtube’s conversions.

  Based on the info about my original MP4 file, can someone suggest some better settings for ffmpeg conversions to WEBM and OGG ? Am I going about this all wrong ? The best I’ve done so far was with a string like this, which specified a high quality and a fairly robust bit rate...

  ffmpeg -i input-file.mp4 -c:v libvpx -crf 10 -b:v 1M -c:a libvorbis output-file.webm

  That was much better than the default settings, but still nowhere near the quality of YOUTUBE conversions. In my resulting WEBM video, you can pretty plainly see how the picture degrades, and will snap into focus every few seconds when a "key frame" comes up. These artifacts should not be so obvious. Thanks for any help.