Question

I want to convert a subtitle time code:

begin="00:00:07.71" dur="00:00:03.67

to pure seconds:

begin=7.1 end=11.38

I wrote a Ruby code:

def to_sec(value)
        a = value.split(':')
        a[0].to_i*3600+a[1].to_i*60+a[2].to_f
    end

which resulted in 11.379999999999999.
Can anybody tell me why this happens?
Is there any Time library that can do this conversion?

Answer 1

It’ll probably be easiest for you to represent your underlying datatype as integer hundredths of a second (centiseconds):

     def to_csec(value) #if you had CSec < Integer this would be `def self.[](value)`
        a = value.split(':')
        #tacking on a couple zeros to each
        a[0].to_i*360000+a[1].to_i*6000+(a[2].to_f * 100).to_i
     end

You could add some helpers for dealing with the durations and pretty printing them as well:

     def csec_to_s(csec) #if you had CSec < Integer, this would be `def to_sec`
        "%.2f" % (csec.to_f / 100)
     end

    class SubtitleDuration < Range
     def initialize(a,b)
        centi_a = to_csec(a)
        super(centi_a,to_csec(b) + centi_a)
     end
     def to_s
       "begin=#{csec_to_s(self.begin)} end=#{csec_to_s(self.end) }"
     end
    end

Then your answer is just:

    puts SubtitleDuration.new("00:00:07.71", "00:00:03.67").to_s 
    #=> begin=7.71 end=11.38