Dive media: Extract thumbnails from videos with ffmpeg

Extract thumbnails using ffmpeg.
Behavior is controlled by three new preferences fields:
 - extract_video_thumbnails (bool): if true, thumbnails are calculated.
 - extract_video_thumbnail_position (int 0..100): position in video
   where thumbnail is fetched.
 - ffmpeg_executable (string): path of ffmpeg executable.

If ffmpeg refuses to start, extract_video_thumbnails is set to false
to avoid unnecessary churn.

Video thumbnails are marked by an overlay.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 263 insertions, 0 deletions

diff --git a/icons/video_overlay.svg b/icons/video_overlay.svg
new file mode 100644
index 000000000..87ad6a6e3
--- /dev/null
+++ b/icons/video_overlay.svg
@@ -0,0 +1,263 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   height="66"
+   width="22"
+   id="svg25756"
+   version="1.1"
+   viewBox="0 0 22 66"
+   sodipodi:docname="video_overlay.svg"
+   inkscape:version="0.92.3 (2405546, 2018-03-11)">
+  <sodipodi:namedview
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1"
+     objecttolerance="10"
+     gridtolerance="10"
+     guidetolerance="10"
+     inkscape:pageopacity="0"
+     inkscape:pageshadow="2"
+     inkscape:window-width="1920"
+     inkscape:window-height="1015"
+     id="namedview870"
+     showgrid="false"
+     inkscape:zoom="12.242424"
+     inkscape:cx="11"
+     inkscape:cy="33"
+     inkscape:window-x="0"
+     inkscape:window-y="0"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg25756" />
+  <metadata
+     id="metadata25760">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs3051">
+    <style
+       id="current-color-scheme"
+       type="text/css">
+      .ColorScheme-Text {
+        color:#4d4d4d;
+      }
+      </style>
+  </defs>
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