Apple has expressed within the framework of two further developer sessions with new details on the use of HEIF and HEVC under iOS and macOS. What is now fixed for decoding and encoding in hardware and software, and how Apple handles the exchange with devices outside its own ecosystem.
The support provided by HEIF will be used by Apple in the future for Live Photos (instead of JPEG + H.264-MOV), while supporting image sequences for the burst mode of the camera will be used. It was also confirmed that Apple goes from a halving of the file size against JPEG.
HEIF uses HEVC as a codec
When Apple creates an image captured with the camera of the smartphone or tablet under iOS 11, HEVC is used as an encoder for the High Efficiency File Format, so that created files bear the extension .heic . Apple also supports H.264 as an encoder for HEIF, but these files must have the extension .avci . All other codecs supported by the system must have the file extension.
Decoding and encoding HEIF and HEVC
HEIF can be decoded from basically all Apple devices with iOS and macOS, but this is only available from the A9 (X) chip of the iPhone 6s (Plus), iPhone SE, iPad Pro (9.7 & 12.9 inch ), IPad 2017 as well as Intel processors from the sixth Core i-Generation (Skylake) possible. On all other devices a software decoder is used for HEIF. Encoding support at the hardware level is exclusively for the A10 (X) Fusion of the iPhone 7 (Plus) and iPad Pro with 10.5 inches as well as 12.9 inches of the second generation. A software encoding is not offered for the mobile devices.
For HEVC in videos, Apple calls a compression factor of up to 40 percent compared to H.264 in the industry. In combination with the iOS camera, however, Apple explicitly names up to twice as strong compression, so here too with half as large files to be expected. Apple supports HEVC’s Main Profile as well as Main Still Picture and Main 10 for 10-bit color depth. The codec type used is hvc1 and the permissible file extensions are as before.
10-bit in hardware can not be a device
According to Apple, all iOS and macOS devices are basically suitable for the decoding of HEVC videos, but again a distinction is made between the decoding in hardware or software. In addition, Apple distinguishes between 8-bit and 10-bit decoding. 8-bit hardware decoding is possible from the A9 (X) chip as well as Intel Skylake processors, while 10-bit hardware decoding is possible again from the A9 (X) chip, but only with Intel Kaby- Processors of the latest MacBook (Pro) and iMac. The software decoding of 8-bit and 10-bit material works with all iOS and macOS devices. The encoding of HEVC in hardware is only possible in 8-Bit from the A10 (X) Fusion as well as the sixth Core i-Generation (Skylake).
Transcoding for e-mail and the share extension
Further details were also given on what happens when HEIF and HEVC are to be shared with other devices or services. Apple goes for two separate ways: Either is always transcodiert or first checked, which abilities the receiving device possesses. If it is not possible to determine the abilities of the recipient – for example, when sending via e-mail or via the share extension in iOS and macOS – Apple always performs a transcoding to the previously used formats JPEG or H. 264. If an app uses Apple’s Connectivity API (P2P) or if AirDrop is used, the receiver can communicate its abilities to the sender at the first handshake, whereupon this HEIF or JPEG or HEVC or H.264 will send.
Before the update on iOS 11 pictures and videos stored on the devices are at least not converted with the first developer preview into the new formats. By default HEIF and HEVC are used for new recordings. However, this can be deactivated by the user in the settings of the camera in the submenu “Formats”, so that again JPEG and H.264 are used. There you can also set whether the transfer to a Mac or PC should automatically decide in which format the files are transferred, or whether the originals should be used.