Astrape Download

The science behind the picture

Every HDR file carries numbers for light and color. Astrape reads them and gets them to your TV intact. These are the curves and color spaces it works with, drawn from the published standards.

SMPTE ST 2084 · ITU-R BT.1886

Light: the PQ curve

PQ 1,000 nits SDR 50.3 nits 10-bit code 769

HDR10 and Dolby Vision describe brightness with PQ, from 0.0001 to 10,000 nits. SDR video tops out near 100. The same signal value means a very different light level, so it has to reach the TV exactly as mastered.

CIE 1931 · ITU-R BT.709 · BT.2020 · DCI-P3

Color: three gamuts

BT.2020 100% P3 71.7% BT.709 52.9% λ 520 nm

The horseshoe is every color the eye can see. 4K HDR is graded inside the BT.2020 triangle; HD video lives in the small BT.709 one. Percentages are the share of BT.2020's area.

Image Details: the picture, measured

Image Details shows what an HDR film's file holds, in five views, without leaving the player.

Astrape's player on Apple TV: a swipe up shows the controls, focus moves left to the Image Details button, and it opens the Light, Colour and Heat Map views. The Martian 2015 · 2 h 24 min · Chapter 7 1:03:24 −1:20:36 PeakAverage As the file states
  1. 1While an HDR film plays, swipe up on the remote.
  2. 2Move left to the first button, Image Details, and click.
  3. 3Swipe along the tabs: Light, Colour, Heat Map, Dolby Vision and Live Overlay.
  • LightHow bright the film is from start to end, drawn above the timeline.
  • ColourWhere the frame's colors fall on the CIE 1931 chart.
  • Heat MapThe paused frame in nits, laid over the picture.
  • Dolby VisionWhat the file's Dolby Vision data says about the shot and its master.
  • Live OverlayA small meter that stays over the film while it plays.

Every number is what the file states or what its pixels measure, and Image Details says which. It never changes the picture that plays.

HTTP/1.1 RANGE REQUESTS · RFC 9110

Streaming: only the bytes it needs

Position 0:56:45 / 2:06:08 Ready ahead 30.0 s Fetched 0 MB of 70 GB Requests 0

A 70 GB film is never downloaded whole. Astrape asks your server for the next few megabytes at a time and keeps about 30 seconds ready ahead of you. Jump anywhere and it asks for that part of the file instead.

Live simulation: 74 Mb/s 4K file, 400 Mb/s home network, real time.