How will HEVC actually work?

Discussion in 'macOS High Sierra (10.13)' started by raymanh, Sep 14, 2017.

  1. raymanh macrumors member

    Aug 27, 2017
    So I understand a new feature is this new more highly compressed codec, but how is this implemented? Is this the new codec that iTunes movies will be downloaded as? Will High Sierra have the option to transcode any h.264 files I have automatically into HEVC?

    For example I have lots of movies on my external drive that are h.264 and some other codecs. How would I take advantage of HEVC with this when I upgrade to High Sierra on the 25th.

  2. br0adband macrumors 6502a


    Aug 29, 2006
    The idea of transcoding h.264 files (lossy by definition and nature) to yet another lossy format, even h.265, is not a good idea and never recommended unless you really don't have a choice and I can't imagine a situation where that kind of transcode is required aside from you or whoever else wanting smaller files. The preferred and recommended solution would be to get the original source material and then do a single generation encode from source to h.265 aka HEVC.

    h.265 HEVC (on paper) offers similar or slightly better visual quality at roughly half the bitrate of h.264 in most situations which results in files that can be up to about 50% smaller (based on just the video stream size, the audio stream content is rarely considered in such calculations). So if you had a 1080p clip that was 1 hour long and came in at about 2GB in size (video and audio streams in the container) in h.264 format as encoded directly from source, you could theoretically end up with a ~1GB file (video and audio streams in the container) in h.265 format also encoded directly from source.

    In a transcode from h.264 to h.265 the result might be even smaller because of the lossy source material so again, using original source material for the single generation encode (meaning Source > h.265 one time) is going to result in the best quality possible.

    Also take into consideration that "defaults" for h.265 encoding don't always end up with the best results so, some hand-tuning of the possible encoding options is going to be highly relevant as well. To get the very best quality with respect to smaller file sizes as the end result you're going to have to do some test encodes to learn how h.265 works (and how it differs from h.264 encoding in those respects).

    h.265 is now coming on pretty strong and with a little bit of GPU assist in the latest generation Intel processors means it won't take as long to encode as it has in the past, obviously, but those encoding options will be the final arbiter in terms of the quality of your resulting encodes so, it's a learning process all over again just like it was for using h.264.
  3. raymanh thread starter macrumors member

    Aug 27, 2017
    I did not realise HEVC (h.265) was more than just an apple thing. Seeing as its just a new standard of compression it'll be such that there will be h.265 compression codecs in cameras, movies and shows will be directly compressed into h.265 and it will be distributed like that. And, now Macs can play that format. Think I've understood that.
  4. EugW macrumors 603


    Jun 18, 2017
    1. As mentioned, you don’t want to transcode. Waste of time and reduced quality. Luckily, iTunes and Photos don’t automatically transcode.

    2. Apple suggests the space savings over h.264 for 1080p to 4K is around 30-40%. Not 50%.

    3. For 4K 8-bit HEVC you need a 6th gen Intel CPU for hardware decode. For 4K 10-bit HDR HEVC you need a 7th gen Intel CPU. I tried a high bitrate 4K 10-bit HDR HEVC file on my 2017 12” MacBook Core m3 (which is the absolute slowest 3017 Mac Apple sells) and it plays fine with 25% usage in High Sierra. Here’s my thread on it.

    Other people have tried the same file on a 2016 Core i7 MacBook Pro and it does NOT play cleanly even at 100% CPU usage because it doesn’t have the hardware support for it. One year too old. Software playback of some 4K HEVC content is going to make older hardware cry. Even 1 year old Core i7 iMacs have trouble with high bitrate and high fps 10-bit HDR material, and current Core i7 7700K iMacs have trouble if forced to use software playback mode (eg. using Sierra, not High Sierra).

    4. I suspect iTunes HEVC will be a lot easier to play on older hardware, and Apple will partially tailor the file formats and bit depths to the hardware downloading the files.
  5. raymanh thread starter macrumors member

    Aug 27, 2017
    My machine is a 2016 MBP 13 non touch so the 10 bit will be out of the option according to you. Since higher compression means that the CPU generally has to work harder to decode, does that mean the playing a h.264 file would make my battery last longer compared to playing a h.265 file?
  6. EugW macrumors 603


    Jun 18, 2017
    With a 2016 MBP, playing an 8-bit h.265 file is fine. However, playing a 10-bit h.265 file will use a lot of battery, and if 4K, won't work very well.

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5 September 14, 2017