It's an MPEG4/h264 file in a program stream
Handbrake isn't the end all/be all. It does a great job, but not every job.
This is a job for ffmpeg. If your'e willing to pay try FFWorks which should handle it. I have the older version (iFFMPEG). If you want to post a sample (via DM) I can test and see if it works.
If you choose to go down the ffmpeg route, once installed, this will help you write the command line to convert it.
> My client gave me footage shot on their iphone in apparently HEVC codec, which my old imac (10.9) can't handle, and apparently the codec is for windows?
HEVC is h265 - the next generation after h264. Modern Macs plus the OS make it possible.
It works on Macs and Windows; Android and iOS.
> I've never heard of this it's completely new to me. When I try to convert it in mpegstreamclip, the audio plays but the video is white.
MPEG streamclip relies on Quicktime 7 - and it never knew about h265/HEVC which is the problem.
> I have a macbook with 10.11 though, and at least on that one VLC can open it. Handbrake can also open them on it but mpegstreamclip still can't.
VLC player uses the command line tool FFMPEG - which can handle many, many codecs.
> In handbrake I believe you can convert to H.264, but that wouldn't be good for editing right?
It depends on the tools you have. I don't know what editorial tool you're using. Adobe Premiere Pro CC (current), which won't work on your system, will handle it if your hardware can.
> ....then again neither would iphone footage so maybe it's a necessary evil here. My 10.9 is better for editing than my 10.11 so I want to use the 10.11 to convert it to something useable on 10.9.
My Hail Mary? At the command line, use FFMPEG to convert it from HEVC to ProRes or DNxHD depending on what editorial tool you're using.
There's a $30 or so utility called FFWORKs that gives FFMPEG a GUI They have an older version that works on 10.9 and 10.11
That's what I was worried about with Sorenson and some of the others I've seen!
Speaking of ffmpeg - I came across this GUI (http://www.ffworks.net/) in the past 24 hours and I'll be damned if it doesn't do a nice job in my limited testing so far.
ffWorks is an excellent ffmpeg GUI for Mac:
It's a paid program, but there is a free trial. If you have all your files queued up at once, then the free trail might be enough for you.
I paid for it, and it was easily worth it. It's an excellent GUI, it allows you to either keep it simple or discover a ton of the hidden features of ffmpeg.
This program along with MakeMKV are easy worth paying for it you intend to archive a ton of DVDs and Blu-Rays.