[jpap]

> I'd be curious if the two "representations" are losslessly convertible, for example.

They are: you could just extract the HEVC NAL units, and re-write them into a MP4 or QuickTime container, making sure to properly place the codec configuration box, etc.

HEIF also goes beyond a sequence of frames, in that it can describe alpha planes, depth maps, tiling, etc. In that case there might not be an analog with a standard video. If you really wanted to decompose a HEIF container, you might choose to extract the raw media into elementary streams (for HEVC or AVC; or if you're using the JPEG codec, just plain JPEG files) adjacent to any metadata like Exif, etc. This is essentially what Nokia's conformance files are [1].

[1] https://github.com/nokiatech/heif_conformance/tree/master/bi...