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HDK
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Classes | |
| struct | flicks_hash |
Typedefs | |
| using | flicks = std::chrono::duration< std::chrono::nanoseconds::rep, std::ratio< 1, 705600000 >> |
Functions | |
| constexpr double | to_seconds (const flicks ns) |
| constexpr flicks | to_flicks (const double s) |
| template<class Rep , class Period > | |
| constexpr flicks | flicks_cast (const std::chrono::duration< Rep, Period > in_duration) |
Variables | |
| constexpr flicks | k_flicks_one_second |
| constexpr flicks | k_flicks_one_twenty_fourth_of_second |
| constexpr flicks | k_flicks_one_ninetieth_of_second |
| constexpr flicks | k_flicks_min_time {std::numeric_limits<flicks::rep>::min()} |
Copyright (c) 2017-present, Facebook, Inc. All rights reserved.
This source code is licensed under the BSD-style license found in the LICENSE file in the root directory of this source tree.
| using util::flicks = typedef std::chrono::duration<std::chrono::nanoseconds::rep, std::ratio<1, 705600000>> |
A flick (frame-tick) is a very small unit of time. It is 1/705600000 of a second, exactly.
1 flick = 1/705600000 second
This unit of time is the smallest time unit which is LARGER than a nanosecond, and can in integer quantities exactly represent a single frame duration for 24 Hz, 25 Hz, 30 Hz, 48 Hz, 50 Hz, 60 Hz, 90 Hz, 100 Hz, 120 Hz, and also 1/1000 divisions of each, as well as a single sample duration for 8 kHz, 16 kHz, 22.05 kHz, 24 kHz, 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, and 192kHz, as well as the NTSC frame durations for 24 * (1000/1001) Hz, 30 * (1000/1001) Hz, 60 * (1000/1001) Hz, and 120 * (1000/1001) Hz.
That above was one hell of a run-on sentence, but it's strictly and completely correct in its description of the unit.
This makes flicks suitable for use via std::chrono::duration and std::ratio for doing timing work against the system high resolution clock, which is in nanoseconds, but doesn't get slightly out of sync when doing common frame rates.
We also support some common audio sample rates as well. This list is not exhaustive, but covers the majority of digital audio formats. They are 8kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz, and 192kHz.
Though it is not part of the design criteria, 144 Hz, which some newer monitors refresh at, does work correctly with flicks.
NTSC IS NOT EXPLICITLY SUPPORTED IN ALL OF ITS SUBTLE NUANCES, BUT: The NTSC variations (~23.976, ~29.97, etc) are approximately defined as 24 * 1000/1001 and 30 * 1000/1001, etc. These can be represented exactly in flicks, but 1/1000 divisions are not available.
Many folks online have pointed out that NTSC technically has a variable frame rate, and that this is handled correctly in other media playback libraries such as QuickTime. The goal of flicks is to provide a simple, convenient std::chrono::duration to work with when writing code that works with simulation and time in media, but not explicitly to handle complex, variable-rate playback scenarios. So we'll stick with the 1000/1001 approximations, and leave it at that!
Details
24 fps frame: 29400000 flicks 25 fps frame: 28224000 flicks 30 fps frame: 23520000 flicks 48 fps frame: 14700000 flicks 50 fps frame: 14112000 flicks 60 fps frame: 11760000 flicks 90 fps frame: 7840000 flicks 100 fps frame: 7056000 flicks 120 fps frame: 5880000 flicks 8000 fps frame: 88200 flicks 16000 fps frame: 44100 flicks 22050 fps frame: 32000 flicks 24000 fps frame: 29400 flicks 32000 fps frame: 22050 flicks 44100 fps frame: 16000 flicks 48000 fps frame: 14700 flicks 88200 fps frame: 8000 flicks 96000 fps frame: 7350 flicks 192000 fps frame: 3675 flicks
NTSC:
24 * 1000/1001 (~23.976) fps frame: 29429400 flicks 30 * 1000/1001 (~29.97) fps frame: 23543520 flicks 60 * 1000/1001 (~59.94) fps frame: 11771760 flicks 120 * 1000/1001 (~119.88) fps frame: 5885880 flicks
| constexpr double util::to_seconds | ( | const flicks | ns | ) |
| constexpr flicks util::k_flicks_min_time {std::numeric_limits<flicks::rep>::min()} |
| constexpr flicks util::k_flicks_one_ninetieth_of_second |
| constexpr flicks util::k_flicks_one_second |
| constexpr flicks util::k_flicks_one_twenty_fourth_of_second |
1.8.6 
