Extract HEVC bitstream with ffmpeg

I would like to extract the raw .265 bitstream from HEVC mkv file. I use this:

ffmpeg.exe -i hevc.mkv -an -vcodec copy -f hevc bitstream.265

I got this error:

Requested output format 'hevc' is not a suitable output format

However, HEVC demuxer is already implemented and I can extract it to uncompressed raw YUV. ffmpeg -formats:

 File formats:
 D. = Demuxing supported
 .E = Muxing supported
D  hevc            raw HEVC video

What is wrong here?

The raw bitstream of H.264/H.265 is typically called the Annex B format. You can create those files with the following FFmpeg commands:

H.265 to Annex B

ffmpeg -i in.mkv -c:v copy -bsf hevc_mp4toannexb out.h265

does the trick with ffmpeg and H.265/HEVC.

H.264 to Annex B

For H.264 it's slightly different:

ffmpeg -i in.mkv -c:v copy -bsf h264_mp4toannexb out.h264

I tried the ffmpeg solution from Sebastian, but it didn't work for me. Here is what I did to get just the H.265 bitstream. I did see that some people suggested setting the output file extension to .bin, but I like h264/h265 as it makes it more clear what kind of bitstream the file contains.

H.265 to Annex B

ffmpeg -i test.mkv -c:v copy -bsf hevc_mp4toannexb -f hevc test.h265

H.264 to Annex B

ffmpeg -i test.mkv -c:v copy -bsf h264_mp4toannexb -f h264 test.h264

NOTE: This also works for .mov files and probably for other formats as well.