Premiere Pro is very glitchy when using HEVC videos from iPhones.

Encode those files using handbrake

You can now shoot prores QTs on your iPhone. That's a simple way to eliminate this issue and gives you a much friendly file for editing. 

I have the same problem constantly since most of my own footage features the HEVC codec and many customers also send me HEVC footage. My sollution to this problem is rather long, depending on your pc and your amount of footage, but always works.

I first convert all of the footage to .M4V through the Aiseesoft Video Converter Ultimate. After that I paste all my clips into premiere, put the speed to 50%. I render them into one file and place that file above the clips in Premiere. Then, I cut them accordingly with the help of the single clips below and I speed them up again (the rendered ones). You have all your clips on your timeline now, which you may not like too much but they wont glitch.

You really don't gotta do that much, its basically a 3 step process. But you will have to wait some time, can do anything else meanwhile.

David

Kevin, Ann Bens told me in a post a few months agothat there were issues with using AME for transcoding hevc footage to a constant frame rate and the tests I tried seemed to confirm this.   If I remember correctly, the transcoded material's audio would be screwed up.   She said to use handbrake to make the material have a constant frame rate.  Is that no longer true if you got a machine that supports Quick Sync technology?  

HEVC from iPhones isn't just  an HEVC issue. It's the VFR nature of the media that causes by far the bigger problem.

VFR is Variable Frame Rate. The frame-rate you have set in the phone is just an 'average' setting, as the actual frame rate jumps dramatically from moment to moment while shooting. The device guesstimates how few frames of video it can get by on for the movement currently happening, and 'shorts' frames during slow movement periods. My Samsung phone media, when set to 30fps, will vary within a clip from around 26.8fps to 31.2fps. The audio is fixed time though.

And the reason iMovie handles that media better is because the "amateur" apps all worked at handling VFR media long before any of the professional apps did. Pro apps had always focused on pro type media, which never used to include any VFR. CFR ... constant frame rate ... was the only type that pro apps used. Premiere finally started working at being able to use VFR media at all just a couple years back, and still ... will work fine with some VFR but others can be dicey.

My Samsung phone media works perfectly ... well, almost all the time ... within Premiere. iPhone HEVC is a rather more "out there" media pushing the format/codec standards out there a bit farther than most other rigs. And is therefore more dicey to work with in Premiere.

Each update, they do improve the VFR handling of Premiere. So it is something that is being worked on. But it's a relatively new ability within the app.

Neil