A clojure wrapper around ffmpeg command line tools.

ffmpeg is an awesome tool. Lets stop just using sh to control it. How about we write a robust system that can:

• Control the many tools included in ffmpeg's ecosystem.
• Keep track of what processes we have spun up.
• Navigate ffmpeg's flag hell with readable sane flags.

This is a wrapper library. Make sure you have ffmpeg installed on your system and runnable through your system path.

Kawa provides both ffmpeg command line tool wrappers as well as a process manager.

To include the command line tools:

kawa.core=> (require '[kawa.core :refer [ffmpeg! ffplay! ffprobe!]])
;nil

To include the process manager:

kawa.core=> (require `[kawa.manager :as manager])
;nil

ffmpeg!, ffplay!, and ffprobe! will all launch an instance of each application. As a simple example, lets generate a test video and store it in a file on your system.

kawa.core=> (ffmpeg! :f "lavfi" :i "testsrc" :t 10 :pix_fmt "yuv420p" "testsrc.mp4")
;{:cmd ["ffmpeg" "-f" "lavfi" "-i" "testsrc" "-t" "10" "-pix_fmt" "yuv460p" "testsrc.mp4"], :process {:out #object[java.lang.UNIXProcess$ProcessPipeInputStream 0x33b2f029 "java.lang.UNIXProcess$ProcessPipeInputStream@33b2f029"], :in #object[java.lang.UNIXProcess$ProcessPipeOutputStream 0x134ec85c "java.lang.UNIXProcess$ProcessPipeOutputStream@134ec85c"], :err #object[java.lang.UNIXProcess$ProcessPipeInputStream 0x375941a4 "java.lang.UNIXProcess$ProcessPipeInputStream@375941a4"], :process #object[java.lang.UNIXProcess 0x3c319941 "java.lang.UNIXProcess@3c319941"]}}

The command returns a map that contains :cmd which holds the exact command run. It also contains :process which holds the return value of conch's sh/proc implementation. The :process value is used by the manager to kill running processes.

As you can see, flags are represented by keywords. There are many quality of life keywords that improve the readability of your code. For example, the below code does the same as above.

kawa.core=> (ffmpeg! :format "lavfi" :input-url "testsrc" :duration 10
                     :pixel-format "yuv420p" "testsrc.mp4")

To check the currently registered processes, you can run:

kawa.core=> (manager/ls)
;{}

The manager is using a namespaced (atom {}) to store information registered. You may find yourself in a situation where you wish to have multiple registries. If this is the case, all 3 kawa.manager functions have an optional first parameter that takes an atom.

kawa.core=> (def my-registry (atom {}))
; #'kawa.core/my-registry
kawa.core=> (manager/ls my-registry)
;{}
kawa.core=> (manager/ls)
;{:test {:cmd ["ffmpeg" "-i" "rtsp://admin:[email protected]:554/media/video1" "-t" "100" "-pix_fmt" "yuv420p" "testsrc.mp4"], :process {:out #object[java.lang.UNIXProcess$ProcessPipeInputStream 0x53d266d "java.lang.UNIXProcess$ProcessPipeInputStream@53d266d"], :in #object[java.lang.UNIXProcess$ProcessPipeOutputStream 0x5eba57f5 "java.lang.UNIXProcess$ProcessPipeOutputStream@5eba57f5"], :err #object[java.lang.UNIXProcess$ProcessPipeInputStream 0x40de6630 "java.lang.UNIXProcess$ProcessPipeInputStream@40de6630"], :process #object[java.lang.UNIXProcess 0x538f1277 "java.lang.UNIXProcess@538f1277"]}}}

In this example, we have no processes registered yet. Lets spin up an ffmpeg process and register it in one go.

kawa.core=> (manager/register :test (ffmpeg! :i "rtsp://admin:[email protected]:554/media/video1" :duration 100 :pix_fmt "yuv420p" "testsrc.mp4"))
; :test

You can then use ls to ensure the process has been successfully registered. If you do not provide an id to register it as, a unique id will be generated for you. register returns the ID of process you just registered.

To kill the process that has been registered, simply run:

kawa.core=> (manager/kill :test)
;Stopping :test
;#future[{:status :ready, :val 0} 0x7549316]

kill returns a future whose value is the exit value that is returned from the shell.

Detailed documentation can be found here

Copyright © 2019 Alexander Maricich

Distributed under the Eclipse Public License version 1.0