Yes, I have put the hwdec=rkmpp etc. flags to mpv.conf. The decoding just fails if trying to play youtube videos. And when using ffmpeg-mpp I have actually deprioritized the hardware codecs from ffmpeg-mpp source because they were giving problems with firefox, and using vd=h264_rkmpp_decoder… parameter to force their use with mpv, as for some reason using hwdec=rkmpp then with ffmpeg-mpp causes mpv to freeze at the end of the video, requiring killing it.
Lines from verbose log that seem to have some relevance to the issue:
[vd] Container reported FPS: 30.000000
[vd] Codec list:
[vd] h264 - H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
[vd] h264_v4l2m2m (h264) - V4L2 mem2mem H.264 decoder wrapper
[vd] h264_qsv (h264) - H264 video (Intel Quick Sync Video acceleration)
[vd] h264_rkmpp (h264) - Rockchip MPP (Media Process Platform) H264 decoder
[vd] Opening decoder h264
[vd] Looking at hwdec h264_rkmpp-rkmpp…
[vo/gpu] Loading hwdec drivers for format: ‘drm_prime’
[vo/gpu] Loading hwdec driver ‘drmprime’
[vo/gpu/drmprime] using EGL dmabuf interop
[vo/gpu/drmprime] Using DRM device: /dev/dri/renderD128
[ffmpeg] AVHWDeviceContext: Opened DRM device /dev/dri/renderD128: driver rockchip version 3.0.0.
[vo/gpu] Loading hwdec driver ‘drmprime-overlay’
[vo/gpu/drmprime-overlay] Failed to retrieve DRM fd from native display.
[vo/gpu] Loading failed.
[vd] Trying hardware decoding via h264_rkmpp-rkmpp.
[vd] Using underlying hw-decoder ‘h264_rkmpp’
[ffmpeg] h264_mp4toannexb: The input looks like it is Annex B already
[vd] Pixel formats supported by decoder: drm_prime nv12
[vd] Codec profile: Main (0x4d)
[vd] Hardware decoding of this stream is unsupported?
[vd] Requesting pixfmt ‘nv12’ from decoder.
[ffmpeg/video] h264_rkmpp: Format nv12 chosen by get_format().
[ffmpeg/video] h264_rkmpp: Created a RKMPP hardware device
[vd] Selected codec: H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
[ffmpeg] detected 8 logical cores
[vf] User filter list:
[vf] scale_rkrga (scale_rkrga.00)
[cplayer] Starting playback…
[ffmpeg/video] h264_rkmpp: Decoder could not get packet, retrying
[ffmpeg/video] h264_rkmpp: Decoder flushing
[vd] Attempting next decoding method after failure of h264_rkmpp-rkmpp.
[vd] Skipping previously attempted hwdec: h264_rkmpp-rkmpp
[vd] Using software decoding.