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• ffmpeg : Frame perfect overlay of two videos

  13 mai 2018, par SuperUser_Novice

  I’m using ffmpeg to overlay two videos, one being a collection of qr codes to be used later to check for streaming errors.

  The problem I’m having is that despite creating a video using the same framerate and number of frames, I can’t get my program to match the frames up in such a way that they overlay frame for frame.

  I haven’t been able to find a way to specify to ffmpeg that it should overlay based on frames rather than duration and timestamps. As a result the zbar scanner is picking up duplicated and dropped frames every 700 or so frames into the video.

  (edit : It was later found that this does not appear to be possible, thus I came up with a very hacky way of getting frame-perfect overlay, detailed in the answers.)

• Correcting color cast with ffmpeg

  16 mai 2018, par Henry H

  I have two videos that have a pretty significant blue cast to them. I took some stills at the same time and I’m happy enough with the colors on those and I’d like to re-encode the videos, adjusting the colors to something similar to the stills.

  • A frame from the original video can be seen here : http://www.dotrose.com/temp/img_20180513_153484_original.png
  • An attempt at correcting the color, which would be acceptable : http://www.dotrose.com/temp/img_20180513_153484_corrected.png
  • A still image taken at the same time (but with some help from a flash) : http://www.dotrose.com/temp/img_20180513_153476.jpg

  I understand I could either create a large collection of jpg images from the video and color correct them before reassembling them into a new video or I could use ffmpeg’s color level’s filter to do it directly. What I don’t know is how to get the numbers to pass to the filter. I’m assuming I want to do something like this :

  ffmpeg -i video.mov -vf "colorlevels=rimin=##/255:gimin=##/255:bimin=#/255:rimax=###/255:gimax=###/255:bimax=###/255, eq=gamma=#.##" -y out.mov

  How do I get the values to use for each of the r, g, and b min and max settings and gamma to use in place of the ###s ? Assuming this is the right approach, of course.

  Update : Perhaps this question would be better asked in a forum for gimp or photoshop. But I know how to adjust the color in those. What I need to know is how I translate those changes to what ffmpeg is expecting.

• Kodi : playback several video files from the internet as single movie with single timeline

  30 mai 2018, par HarryFox

  I’m writing an add-on for Kodi in Python, for a site with movie collection, which can be able to playback online video from the site. But problem is that many of them splitted apart on pieces of different length. And its not mpeg dash nor m3u playlists, its just individual pieces of single movie or an episode.

  My target is able to play those splitted videos as single movie with single timeline and playback will no require download all pieces of a movie. It’s important because many of Movies\episodes provides with subtitle file, that why single timeline is important. Also general idea for plugin which I’m writing is comfort to use, so online playback is very important too.

  I did some research but it almost no result. On official Kodi forum advise to create Input Stream add-on like Input Stream Adaptive, but it was written on c++ and it’s unattainable for me (for now at least). There is no tools for python to create such kind of add-ons.

  Another idea is to create middle server which on fly will somehow (with ffmpeg) combine those pieces, but it seems that the process will too resource-intensive especially for TV-boxes.
  In this case also raise many question about which way is better, and i have no enough experience and knowledge to solve the problems by myself even with google.

  So i need an advice how can i solve the problem, just to know right direction.
  Thank you for your time.
  Sorry for my English.