The newest machines from DJI, including the Phantom 4 Pro/Adv and Inspire 2, now have the ability to select H.265 for video encoding. The advantage of H.265 is that it can achieve up to 50% more data in the same file size as H.264. In theory, this is a great idea if it allows for a way to get even better image quality. There are however some important things to note before you make the decision to use H.264 or H.265.
The first thing to know is how DJI implemented the H.265 codec. Instead of providing improved image quality without increasing file size, the DJI implementation actually has the same image quality as H.264 but results in smaller file sizes. While, at first, this seems like a great way of reducing file storage, there is a bit more to understanding if H.265 is a better choice for you.
One of the big issues in using H.265 is actually editing the files. The H.265 codec is extremely CPU intensive and even high-end computer systems will have difficulty in smoothly playing the H.265 files. Even software like Adobe Premiere, while it can open H.265, can't play it back smoothly enough to edit it. One of the only editing tools that does a decent job with H.265 is Davinci Resolve 14 Studio ($299). Apple's Final Cut Pro X, as of 5/2017, will not even see the H.265 files.
To effectivly use the H.265 files, you need to transcode them into a codec that your editor can handle easily. The best choice to transcode to is ProRes 422 LT as it can handle the data without adding any compression to the files.
The problem with transcoding to ProRes 422 LT is that the transcoding process results is a much larger file then you started with. We started with an H.265 file that was 221.4 MB. After transcoding, the ProRes file was 868.6 MB. Granted, you can delete the ProRes file later when you are done editing, but it does take up a significant amount of disk space, even if temporairily.
File Size Comparison
As for image quality, there is no advantage today in using H.265, except in some very specific high-speed, fine detail situations that are not common for aerial video. If you are only going to get a smaller file that needs to be transcoded, and is harder to edit, there isn't any real reason to use H.265. Another disadvantage of H.265 is that you lose the ability to use 4k/60 as H.265 can only do 4k/30.
Unless DJI changes their implementation of H.265 to provide more data in the same file size, there is just not enough of an advantage of H.265 to recommend using it as this time.