Totem ignoring hardware acceleration

Totem is ignoring available hardware decoders (e.g. vaapi). mpv and gst-play-1.0 both use it. Playback of 4K video is impossible on Haswell i7.

This is probably not a gstreamer issue, because gst-play-1.0 uses the acceleration just as expected. This can be verified using intel_gpu_top.

$ gst-inspect-1.0 vaapi
Plugin Details:
  Name                     vaapi
  Description              VA-API based elements
  Filename                 /usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstvaapi.so
  Version                  1.16.1
  License                  LGPL
  Source module            gstreamer-vaapi
  Source release date      2019-09-23
  Binary package           gstreamer-vaapi
  Origin URL               http://bugzilla.gnome.org/enter_bug.cgi?product=GStreamer

  vaapijpegdec: VA-API JPEG decoder
  vaapimpeg2dec: VA-API MPEG2 decoder
  vaapih264dec: VA-API H264 decoder
  vaapivc1dec: VA-API VC1 decoder
  vaapipostproc: VA-API video postprocessing
  vaapidecodebin: VA-API Decode Bin
  vaapisink: VA-API sink
  vaapimpeg2enc: VA-API MPEG-2 encoder
  vaapih264enc: VA-API H264 encoder

  9 features:
  +-- 9 elements

$ lspci | grep -i graphic
00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09)

$ lscpu 
[...]
Model name:                      Intel(R) Core(TM) i7-4578U CPU @ 3.00GHz