[FFmpeg-user] hw_decode.c on osx?

[su.00048 at cherry.org]

i have ffmpeg building successfully on osx (10.14.6; xcode 11.3.1),
and am using the generated libraries in a personal video project i'm
working on.  now i'm ready to start thinking about implementing hardware
decoding ...  i tried adapting some of the code from hw_decode.c, but 
ran into runtime errors.  thinking that it was my code that was at
fault, i then compiled hw_decode by itself, but i get the same errors
even there.  is anyone aware of hw_decode.c not working on osx?

trying to decode known good videos, either h264 or hevc, results in
some internal errors (see below).  the videos behave as expected when
opened with my locally built versions of ffplay or ffmpeg, however.

h264 example:

    % hwdecode videotoolbox h264.mov h264.out

    [h264 @ 0x7f8a2b003e00] get_buffer() failed
    Assertion src->f->buf[0] failed at libavcodec/h264_picture.c:70
    Abort

hevc fails differently:

    % hwdecode videotoolbox hevc.mov hevc.out

    [hevc @ 0x7f8464814600] get_buffer() failed
    [hevc @ 0x7f8464814600] videotoolbox: invalid state
    [hevc @ 0x7f8464814600] hardware accelerator failed to decode picture
    Error during decoding
    Error during decoding

there are no significant warnings, etc., when building the executable,
so i'm pretty sure everything is ok there.  videotoolbox shows up as
being available in the output of configure.  

any suggestions as to what might be going wrong?  

thanks.