Hi

When playing back content generated using videotestsrc pattern 1 (snow), there seems to be keyframe loss (green frames probably related to decoding error concealing by libav h264 decoder). Frame 1 displays properly, but frame 2 isn't properly decoded (see attachments)

mpv / mplayer / ffprobe etc... reports "Truncated VUI" warnings, not sure if that's really related.

Video has been generated using:
gst-launch-1.0 videotestsrc pattern=1 num-buffers=60 ! timeoverlay ! "video/x-raw,format=(string)I420,width=(int)1920,height=(int)1080,framerate=(fraction)30/1" ! vaapiencode_h264 rate-control=cbr bitrate=40000 ! mp4mux ! filesink location=test.mp4

GST_DEBUG=3 gst-launch-1.0 filesrc location=test.mp4 ! qtdemux ! avdec_h264  ! xvimagesink -v
...
0:00:00.019065136 29849 0x7ffbe0001900 ERROR                  libav :0:: SEI type 191 truncated at 96

And vaapi fails to decode:
GST_DEBUG=3 gst-launch-1.0 filesrc location=test.mp4 ! qtdemux ! vaapidecode ! vaapisink
0:00:00.091122654 30055      0x1eab230 WARN       codecparsers_h264 gsth264parser.c:1216:gst_h264_parser_parse_sei_message: Bit non equal to one.
0:00:00.091192751 30055      0x1eab230 WARN       codecparsers_h264 gsth264parser.c:1229:gst_h264_parser_parse_sei_message: error parsing "Sei message"
0:00:00.091200918 30055      0x1eab230 WARN                   vaapi gstvaapidecoder_h264.c:1605:parse_sei: failed to parse SEI messages
0:00:00.091213060 30055      0x1eab230 ERROR            vaapidecode gstvaapidecode.c:795:gst_vaapidecode_parse_frame: parse error 8