gistfile1.txt

(defn get-length
  [path]
  (let [cmd (str
             "ffmpeg -i '"
             path
             "' 2>&1 | grep Duration | cut -d ' ' -f 4 | sed s/,//"
             )
        output (.start (ProcessBuilder. (into-array ["/bin/bash" "-c"  cmd])))
        info (slurp (.getInputStream output))]

    (let [[h m s] (clojure.string/split info #":" ) ]
      (+
       (* (Long/parseLong h ) 60 60)1
       (* (Long/parseLong m) 60)
       (Float/parseFloat s)))))

;; This might be easier to use on Windows, since I removed grep and split and perhaps bash/sh dependencies

(require '[clojure.java.shell :refer [sh]])
(require '[clojure.string :as str])
(defn get-length
  [path]
    (let [ out (sh "ffmpeg" "-i" path)
           outall (let [{:keys [out err]} out] (str out err))
           DurationLine (apply str (filter #(.contains % "Duration") (str/split outall #"\n")))
           duration (str/split (first (str/split DurationLine #",")) #":")
           [_junk h m s] duration ]
      (+
       (* (Long/parseLong (str/trim h) ) 60 60)1
       (* (Long/parseLong m) 60)
       (Float/parseFloat s))))

(def path "/mnt/big/backup/somefile.mpg")
(get-length path)