Time restraints with Ffmpeg

Question

I am using Ffmpeg to record video in a rails app. I want to give the user a minimum and maximum time limit. What is the best flag to use to set this restraint?

Answer 1

In ffmpeg use the -t (or -to) option to set the duration. Example for 120 seconds:

-t 120

or

-t 00:02:00

See FFmpeg Documentation.

Answer 2

That's a bit beyond the scope of the basic validation that Paperclip does. Paperclip tries to gives you enough validations to cover 95% of your use cases, but for anything that's just a bit less than typical, you'll have to write your own logic. I don't believe there is a custom validation built-in for checking the length of videos. (However, there is a validates_attachment_size validation method you can use for validating the filesize of the asset. In a pinch, this might suffice.)

If you want to do some deeper validations on paperclip attachments, you should look into some different tools to write your own validation methods with. I'd take a look at streamio-ffmpeg if you're dealing with video.

Using that gem you could write a custom validation something like this:

class YourModel < ActiveRecord::Base
  has_attached_file :your_media
  validate :duration_in_range

  private

  def duration_in_range
    # See https://github.com/streamio/streamio-ffmpeg#usage
    unless FFMPEG::Movie.new(your_media.path).duration.in?(MIN_TIME..MAX_TIME)
      errors.add(:your_media, "Video duration must be within #{MIN_TIME} and #{MAX_TIME} seconds")
    end
  end
end