What the HEIC? Apple’s Highly Compressed Image Format Still Confuses

To store more photos and videos on a mobile device, you can either buy more storage or increase image compression. Apple has enabled both paths. It expanded maximum storage so that a 256 GB iPhone isn’t ludicrously expensive. But that gets you only part of the way there.

In 2017, Apple added support for successors to JPEG for images and H.264 for video:

  • HEIF (High-Efficiency Image File Format) is a container format that allows extensive metadata, still images, and sequences (like bursts or Live Photos) to co-exist in a single file.
  • HEVC (High-Efficiency Video Coding), also known as H.265, can encode video using 40–50% less data than H.264 while maintaining the same quality.

(For the technical nitty-gritty, read “HEVC and HEIF Will Make Video and Photos More Efficient,” 30 June 2017.)

Despite all of this happening nearly three years ago, we at TidBITS found ourselves scratching our heads recently about HEIF and HEVC. While Apple uses those terms, files created using those schemes are stored, respectively, with the filename extensions .heic and .mov. (This came up because of the College Board mishandling iPhone images. See “Take a HEIC: Make Sure AP and Other Test Uploads Work from Your iPhone and iPad,” 21 May 2020.)

The former, HEIC, apparently stands for High Efficiency Image Container—more on that in a moment. The latter is potentially even more confusing since MOV files have been around for decades. MOV is a video container format that can hold media encoded in many different ways, including HEVC.

The High Efficiency camera settingApple discusses HEIF and HEVC in various places, including in Settings > Camera > Formats, where you choose between High Efficiency for the newer formats and Most Compatible for JPEG and H.264—though H.264 is also stored in a MOV container. But the company doesn’t mention HEIC or the use of MOV for storing HEVC—even on the page on which it explains HEIF and HEVC.

Since we couldn’t easily sort it out despite the fact that we live and breathe this kind of thing, we spent some time teasing it all apart for you.

HEVC

H.265, which is just another name for HEVC, provides substantial improvements in compression by being more clever and versatile in analyzing individual frames of video and then equally smart in storing differences between adjacent frames. HEVC can compress still images or sequences of video.

HEIF

HEIF is a container format developed by the Moving Picture Experts Group, which has created many licensed audio and video formats. HEIF is used for still images, whether an image stored by itself; with added modification layers (such as from an image-editing program), alpha masking, and depth layers; or sequences (such as a burst mode) and simple animation (as with Live Photos).

You can think of a container format as a sort of folder within a file. Older image formats like GIF, JPEG, PNG, and TIFF pack metadata into the image file, usually at the start. A long-ago change to GIF allowed the integral storage of multiple frames for animations, and TIFF can support multiple pages in a single file. But each of these options requires, in effect, unpacking the entire file. Because HEIF is a container, each discrete image or sequence has its own file within the container, and metadata is stored in separate files as well. It’s a more robust, more compatible way to ensure files can be read across systems, even far into the future.

HEIC

A HEIC file is one specific way to use HEIF, in which the HEIF container relies only on HEVC to encode images. Other operating systems, camera software, and image-editing apps may produce or support variations on HEIF, like AVCI, which uses the AVC (Advanced Video Coding) encoder to store data within HEIF.

With iCloud Photos enabled, you can see the .heic extension on images synced from an iPhone to Photos for macOS. iOS is careful about exporting, however, so your HEIC files may be converted to a JPEG image (for still images) or a JPEG and an H.264 MOV file (for Live Photos) if iOS thinks the receiving device can’t display HEIC.

MOV

HEVC videos are packaged inside MOV containers. Without inspecting them further, there’s no way to know whether or not they contain H.265 data—which requires iOS 11 or later or macOS 10.13 High Sierra or later—or whether they contain H.264-encoded video that will play on older devices. As with HEIC, iOS may export an H.264-encoded MOV file unless it can determine the destination can read HEVC/H.265.

You can check a MOV’s internal encoding formats by opening it in QuickTime Player in macOS and choosing Window > Show Movie Inspector. Under Format, the inspector will display the encoding video and audio formats, as well as dimensions and other details.

Movie info in QuickTime

I hope that clears things up, at least a little. In short, HEIC is Apple’s flavour of HEIF that relies solely on HEVC for compression for still images. For the HEVC-compressed video, Apple continues to use MOV containers.

Article by Glenn Fleishman from tidbits.com