The following patch now avoids breaking ffmpeg-3.4.

From f4406df33f1ed6dd64757f43ea7354fd5a88d2d3 Mon Sep 17 00:00:00 2001
From: Arne Babenhauserheide <arne_bab@web.de>
Date: Sat, 12 Jan 2019 01:24:58 +0100
Subject: [PATCH]     gnu: Add libaom and activate AV1 support in ffmpeg.

    * gnu/packages/video.scm (libaom): New variable.
    * gnu/packages/video.scm (ffmpeg): Add libaom support.
    [inputs] new input libaom.
    [arguments] new configure-flag --enable-libaom.
    * gnu/packages/video.scm (ffmpeg-3.4): filter out libaom.
    [inputs] remove inherited libaom
    [arguments] remove inherited configure-flag --enable-libaom
---
 gnu/packages/video.scm | 45 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/video.scm b/gnu/packages/video.scm
index 947c498c0..a2d56293f 100644
--- a/gnu/packages/video.scm
+++ b/gnu/packages/video.scm
@@ -237,6 +237,40 @@ A/52 standard is used in a variety of applications, including digital
 television and DVD.  It is also known as AC-3.")
     (license license:gpl2+)))
 
+(define-public libaom
+  (package
+    (name "libaom")
+    (version "22b150bf040608028a56d8bf39e72f771383d836") ;; master
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://aomedia.googlesource.com/aom/")
+                    (commit version)))
+              (file-name (git-file-name name version))
+              (sha256
+               (base32
+                "1pdd5h3n42607n6qmggz4yv8izhjr2kl6knb3kh7gh4v0vy47h1r"))))
+    (build-system cmake-build-system)
+    (native-inputs
+     `(("git" ,git)
+       ("perl" ,perl)
+       ("pkg-config" ,pkg-config)
+       ("python" ,python))) ; to detect the version
+    (arguments
+     `(#:tests? #f  ;no check target
+       #:configure-flags
+         ;; build dynamic library
+       (list "-DBUILD_SHARED_LIBS=YES"
+             "-DENABLE_PIC=TRUE"
+             "-DAOM_TARGET_CPU=generic"
+             (string-append "-DCMAKE_INSTALL_PREFIX="
+                              (assoc-ref %outputs "out")))))
+    (home-page "https://aomedia.googlesource.com/aom/")
+    (synopsis "AV1 Codec Library")
+    (description "libaom is the reference encoder of AV1.")
+    (license license:bsd-2)))
+
+
 (define-public libmpeg2
   (package
     (name "libmpeg2")
@@ -701,6 +735,7 @@ standards (MPEG-2, MPEG-4 ASP/H.263, MPEG-4 AVC/H.264, and VC-1/VMW3).")
        ("opus" ,opus)
        ("ladspa" ,ladspa)
        ("lame" ,lame)
+       ("libaom" ,libaom)
        ("libass" ,libass)
        ("libbluray" ,libbluray)
        ("libcaca" ,libcaca)
@@ -787,6 +822,7 @@ standards (MPEG-2, MPEG-4 ASP/H.263, MPEG-4 AVC/H.264, and VC-1/VMW3).")
          "--enable-fontconfig"
          "--enable-gnutls"
          "--enable-ladspa"
+         "--enable-libaom"
          "--enable-libass"
          "--enable-libbluray"
          "--enable-libcaca"
@@ -869,7 +905,14 @@ audio/video codec library.")
                                  version ".tar.xz"))
              (sha256
               (base32
-               "0b59qk5wpc5ksiha76jbhb859g5gxa4w0k6afh3kgvgajiivs73l"))))))
+               "0b59qk5wpc5ksiha76jbhb859g5gxa4w0k6afh3kgvgajiivs73l"))))
+    (arguments
+     (substitute-keyword-arguments (package-arguments ffmpeg)
+       ((#:configure-flags flags)
+        `(delete "--enable-libaom" ,flags))))
+    (inputs (fold alist-delete
+                  (package-inputs ffmpeg)
+                  '("libaom")))))
 
 (define-public ffmpegthumbnailer
   (package
-- 
2.19.2



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