Help with vaapisink

Hello,
I'm trying to test a simple pipeline using VA-API components, I'm running it on an custom system without any window manager (Yocto distribution), the goal is to use DRM, the pipeline is the following:

gst-launch-1.0 filesrc location=$1 ! qtdemux ! queue ! h264parse ! vaapih264dec ! vaapipostproc ! 'video/x-raw(memory:VASurface),format=BGRx'! vaapisink display=4 display-name=/dev/dri/renderD128

The pipeline works correctly and reaches the PLAYING state but I don't see anything on the HDMI monitor, if I use fbdevsink instead I see the decoded video (but obviously it consumes a huge amount of CPU).

Hereafter some additional information:

root@mn-el00d08919cf41:~# vainfo
error: can't connect to X server!
libva info: VA-API version 1.14.0
libva info: User environment variable requested driver 'i965'
libva info: Trying to open /usr/lib/dri/i965_drv_video.so
libva info: Found init function __vaDriverInit_1_14
libva info: va_openDriver() returns 0
vainfo: VA-API version: 1.14 (libva 2.14.0)
vainfo: Driver version: Intel i965 driver for Intel(R) Broxton - 2.4.1
vainfo: Supported profile and entrypoints
      VAProfileMPEG2Simple            : VAEntrypointVLD
      VAProfileMPEG2Main              : VAEntrypointVLD
      VAProfileH264ConstrainedBaseline: VAEntrypointVLD
      VAProfileH264ConstrainedBaseline: VAEntrypointEncSlice
      VAProfileH264ConstrainedBaseline: VAEntrypointEncSliceLP
      VAProfileH264Main               : VAEntrypointVLD
      VAProfileH264Main               : VAEntrypointEncSlice
      VAProfileH264Main               : VAEntrypointEncSliceLP
      VAProfileH264High               : VAEntrypointVLD
      VAProfileH264High               : VAEntrypointEncSlice
      VAProfileH264High               : VAEntrypointEncSliceLP
      VAProfileH264MultiviewHigh      : VAEntrypointVLD
      VAProfileH264MultiviewHigh      : VAEntrypointEncSlice
      VAProfileH264StereoHigh         : VAEntrypointVLD
      VAProfileH264StereoHigh         : VAEntrypointEncSlice
      VAProfileVC1Simple              : VAEntrypointVLD
      VAProfileVC1Main                : VAEntrypointVLD
      VAProfileVC1Advanced            : VAEntrypointVLD
      VAProfileNone                   : VAEntrypointVideoProc
      VAProfileJPEGBaseline           : VAEntrypointVLD
      VAProfileJPEGBaseline           : VAEntrypointEncPicture
      VAProfileVP8Version0_3          : VAEntrypointVLD
      VAProfileVP8Version0_3          : VAEntrypointEncSlice
      VAProfileHEVCMain               : VAEntrypointVLD
      VAProfileHEVCMain               : VAEntrypointEncSlice
      VAProfileHEVCMain10             : VAEntrypointVLD
      VAProfileVP9Profile0            : VAEntrypointVLD

root@mn-el00d08919cf41:~# lshw -disable mmc -c video
  *-display
       description: VGA compatible controller
       product: HD Graphics 500
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 0b
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:129 memory:90000000-90ffffff memory:80000000-8fffffff ioport:3000(size=64) memory:c0000-dffff


Am I missing something?

Thanks,
Davide