From: Steinar H. Gunderson Date: Tue, 29 Jan 2019 21:50:36 +0000 (+0100) Subject: Document the master speed. X-Git-Url: https://git.sesse.net/?p=nageru-docs;a=commitdiff_plain;h=19b8c132bbba57df4209cef2f277a2cc5d61d4c0 Document the master speed. --- diff --git a/futatabi.rst b/futatabi.rst index e17d737..e8370ae 100644 --- a/futatabi.rst +++ b/futatabi.rst @@ -121,6 +121,53 @@ visible in the top screen and go out live over the network to Nageru. Controlling the playback speed '''''''''''''''''''''''''''''' +Most slow motion is at 0.5x speed (or equivalently, “2x slow motion”), +and when you queue a clip from the clip list to the playlist, this is what +it gets by default. However, you are free to change it to whatever you wish, +like 0.333x, 0.25x (both are fairly common “super slow” standards) or even 1.0x. +As long as you are reasonably close to a rational number with low integers +(e.g. 1/2, 2/3, etc.), Futatabi will do its best to try to reuse as many +original frames as possible, keeping quality and performance at their highest +levels. + +In addition to the per-clip speed, it is often interesting to change the +speed *during* playback of a clip. For instance, you could keep normal +slow motion (0.5x) speed in the run-up to a shot, ramp down to 0.1x to get +a good look at the actual shot, and then ramp back once it's done. +When done right and not overused, this can create a dramatic effect that's +hard to replicate using constant slowdown. + +To this effect, Futatabi supports a *master speed* control. It is found at +the bottom of the window (or you can :ref:`control it using a MIDI device `); +note that by default, it is locked at 100% until you click the lock button +to unlock it. (This is particularly important when using a MIDI device, where it is very easy +to touch a slider inadvertedly, and very hard to set it back exactly at 100%.) +The master speed control is multiplied in on top of all other speed factors, +so if you have e.g. a clip at 0.5x and the master speed is set to 70%, +the clip will effectively play back at 0.35x. The master speed can be set between +10% and 200%, inclusive. + +Note that the master speed control governs the speed of the *output* clock, +unlike any other speed control in Futatabi. In particular, this means that unlike +the regular clip speeds, it affects fade times; if fade time is at 0.5 seconds +and master speed is set to 70%, the fade will take approximately 0.714 seconds +(0.5 divided by 0.7). It also means that the “remaining time” displays will be +wrong if master speed is not at 100%. This is because the master speed +is by nature unpredictable (the user can change it at any time); one cannot +e.g. delay fades when the master speed is reduced, since turning it back up +would mean the start of the fade were simply missed. Similarly, it is impossible +to give a proper estimate of time remaining that takes master speed into account; +it would be overestimating time significantly, given that the operator is likely +to turn it back up to 100% again soon. + +Finally, note that when changing master speed, the speed is no longer at a +rational, so most frames will be interpolated frames. If your GPU is not fast +enough to interpolate every frame (ie., it is reliant on Futatabi's usual +reuse of original frames), it will drop output frames. Normal behavior will +resume from the next clip, when the clocks will again go in lockstep (assuming the master +speed is at 100% at that point). If you're not ramping, or if you're done ramping, +it's recommended to keep the speed lock on to avoid inadvertedly changing the speed. + .. _coop: Working with your producer