gnu: transcode: Build with a newer ImageMagick.

* gnu/packages/imagemagick.scm (imagemagick-next): New public variable.
* gnu/packages/video.scm (transcode)[inputs]: Change from IMAGEMAGICK to
IMAGEMAGICK-NEXT.

gnu/packages/imagemagick.scm

@@ -7,6 +7,7 @@
 ;;; Copyright © 2017 Efraim Flashner <efraim@flashner.co.il>
 ;;; Copyright © 2018, 2019 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2018 Alex Vong <alexvong1995@gmail.com>
+;;; Copyright © 2020 Marius Bakke <marius@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -124,6 +125,20 @@ transform images, adjust image colors, apply various special effects, or draw
 text, lines, polygons, ellipses and Bézier curves.")
     (license (license:fsf-free "http://www.imagemagick.org/script/license.php"))))
 
+;; XXX: 'transcode' fails to detect the above ImageMagick, so we provide
+;; this newer version.
+(define-public imagemagick-next
+  (package
+    (inherit imagemagick)
+    (version "6.9.11-37")
+    (source (origin
+             (method url-fetch)
+             (uri (string-append "mirror://imagemagick/ImageMagick-"
+                                 version ".tar.xz"))
+             (sha256
+              (base32
+               "19r6fyhr1bycx0p6jz034mil1zh2k7hfr02is40h4g3wf9b9sdni"))))))
+
 (define-public perl-image-magick
   (package
     (name "perl-image-magick")

gnu/packages/video.scm

@@ -245,7 +245,7 @@
        ("faac" ,faac)
        ("ffmpeg" ,ffmpeg)
        ("freetype" ,freetype)
-       ("imagemagick" ,imagemagick)
+       ("imagemagick" ,imagemagick-next)
        ("lame" ,lame)
        ("liba52" ,liba52)
        ("libdv" ,libdv)