Since the springupdate 12.1 - april, mediaencoder on OSX 10.13.4 became totally useless / unpredictable.
First is that encoding to HEVC is now missing the "max bitrate" setting. Only "target bitrate" is available.
Whatever I select, ME creates extreme huge temp. M4V files .
For example: HEVC traget 13Mbit/s estimatetd 3000MByte VBR = creates files of 25 GB..then tries to multiplex to a MP4 file, and therefor consumes every available discspace (up to 55GB in my case)...the OSX raises a warning ...running out of diskspace....the now created MP4 has now 11GB and is only playing halfway.

If set to CBR , hardware accelaration is not selectable....your system does not support hardware accelerated.... (we are talking about a brandnew IMACPRO with ATI-Graphics !!!)

Set to VBR ...(see above).

ME is randomly crashing and telling me various TC's where the estimated error should be ....

tried this with various timelines and material ...always the same ...
...reverting back to V 12.01 ...everything is fine .

IMAC Pro 8core ATI Graphics 32GB RAM
OSX 10.13.4