Gstreamer 1.22 and h265 with alpha

Bill Hofmann bill at
Thu Jan 26 01:32:01 UTC 2023

So, I've got a 1080p HEVC 8bit/component file encoded with alpha. I've
verified that, for instance, if I play that mp4 file on, it is in fact valid and has
alpha (Safari on Mac Ventura), so using Apple's HEVC decoder I expect.

When I play it using gst-play:

GST_PLUGIN_FEATURE_RANK=vah265dec:9999 GST_DEBUG=2,buffer*:1 gst-play-1.0
--use-playbin3 --videosink="kmssink connector-id=308 plane-id=31
skip-vsync=true" /media/views/content/views/redmonster.mp4

I get a passel of these errors:

0:00:00.069814340 20898 0x7feab00205e0 WARN             h265decoder
gsth265decoder.c:733:gst_h265_decoder_preprocess_slice:<vah265dec0> Current
picture is not finished but slice header has first_slice_segment_in_pic_flag
0:00:00.069829360 20898 0x7feab00205e0 WARN            videodecoder
gstvideodecoder.c:4795:_gst_video_decoder_error:<vah265dec0> error: Failed
to decode data

And no picture, or no useful picture.  When instead I use an HLS segmented
version of it, I *DO* get a picture, but a bad one - it seems to see the
mask, but not be able to render the image.

Good news is that a vp9/webm version with alpha *does* play like a charm
using the same magic gst-play command line.

Any thoughts on diagnosing the issue? Is it just "vah265dec doesn't support
alpha" or is it something more complex?


Bill Hofmann
+1 (510) 387-0952
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