I'm trying to create video in Unity game using AVPro. I use Update function to save frame. targetFrameRate matches video frame rate, so it takes 1 minutes to generate video with 1 minute length.
Is it possible to speed up this process? I tried to use timeScale, but video is length is also dependent on that.
You can use Time.captureFramerate = framerate
From the documentation https://docs.unity3d.com/ScriptReference/Time-captureFramerate.html.
If this property has a non-zero value then frame update will occur at
an interval of (1.0 / captureFramerate) regardless of real time and
the time required to render a frame.
To be able to use this method your code must support it with proper use of Time.deltaTime or a corresponding way.
Related
I'm new to Unity and I see many times that Time.deltaTime needs to be added. In which cases should I add it? I know this is so that there will be no excess power in the event of a quick refresh of the frame's computer.
For example, in the next case, do I need to add Time.deltaTime?
playerRigidbody.AddForce(Vector3.up * 100 * Time.deltaTime, ForceMode.Impulse);
Time.deltaTime is the amount of seconds it took for the engine to process the previous frame. It's calculation is rather simple: it uses the system's internal clock to compare the system time when the engine started processing the previous frame to the system time when the engine started processing the current frame. Every motherboard has a "system clock" which is responsible to keep track of time. Operating systems have access to that system clock and provide API's to read that clock. And Unity gets the time from that API and that's how things are synchronized.
Think of a game as a movie, which is essentially a sequence of images. The difference is that a movie is rendered at a fixed rate of 24 images per second, while a game doesn't have a fixed frame rate.
In a movie, if a car travels at 1 meter per second, each image will make it move by 1/24 meter, and after 24 images (1 second) the car will have traveled exactly 1 meter. It's easy because we know that each frame takes exactly 1/24 second.
In a game, we have to do the same thing, except the frame rate varies. Some frames can take 1/60 second, some others can take 1/10 second. We can't use a fixed ratio. Instead of a fixed number we have to use Time.deltaTime. Each frame, the car will move a distance proportional to the time of the frame. After roughly 1 second, the car will have traveled roughly 1 meter
Delta is the mathematical symbol for a finite difference. Its use is very common in english when talking about something that changed over time.
deltaTime is a difference of time, so it's a Delta
Shorter Terms
You must always use Time.deltaTime when moving objects over time, either by supplying it yourself or by making use of functions like SmoothDamp that use Time.deltaTime by default (hardly any functions do that though). But you must never use Time.deltaTime for input that's already framerate-independent, such as mouse movement, since in that case using Time.deltaTime will do the opposite of what you intend.
If you're ever unsure you can always toggle vsync on and off and observe any potential speed differences. If the game's already running close to the monitor refresh rate anyway, then make use of Application.targetFrameRate instead.
In very easy words
Time.deltaTime is the time passed since last frame was rendered.
By multiplying a value with it you basically convert it from Something per frame into Something per second.
Is it needed?
Now if you need to use it totally depends on your specific use-case! In your case for AddForce: NO!.
The force influences the velocity of a physics object. The velocity itself already is an absolute per second vector.
Usually there are two use-cases for AddForce:
It is called continuously but within FixedUpdate
Because FixedUpdate is not called every frame anyway but rather on a fixed real time intervals (by default 0.02 seconds) you would not need Time.deltaTime. The Doc already provide this in the example.
It is anyway called only as a single event (e.g. by jumping)
Here there is nothing continuous, so you don't need and don't want to use Time.deltaTime either since a single event can not be frame-rate-dependent anyway.
world.
I have many videos that I want to compare one-to-one to check if they are the same, and get from there the delay of frames, let's say. What I do now is opening both video files with virtualdub and checking manually at the beginning of video 1 that a given frame is at position, i.e., 4325. Then I check video 2 to see the position of the same frame, i.e., 5500. That would make a delay of +1175 frames. Then I check at the end of the video 1 another given frame, position let's say 183038. I check too the video 2 (imagine the position is 184213) and I calculate the difference, again +1175: eureka, same video!
The frame I chose to compare aren't exactly random, it must be one that I know it is exactly one I can compare to (for example, a scene change, an explosion that appears from one frame to another, a dark frame after a lighten one...) and I always try to check for the first comparison frames within the first 10000 positions and for the second check I take at the end.
What I do next is to convert the audio from video 1 to video 2 calculating the number of ms needed, but I don't need help with that. I'd love to automatize the comparison so I just have to select video 1 and video 2, nothing else, that way I could forget forever virtualdub and save a lot of time.
I'm tagging this post as powershell too because I'm making a script where at the moment I have to introduce the delay between frames (after comparing manually) myself. It would be perfect that I could add this at the beginning of the script.
Thanks!
I have come up with an algorithm on Matlab, that permits me to recognize hand gestures on prerecorded videos. Now, I would like to run the same code but for real time video this time, I am not sure how to do it after putting these 2 lines:
vid=videoinput('winvideo',1);
preview(vid);
(real time video is on)
I am thinking about a loop : while the video is on, snap repeatedly some images in order to analyze them.
for k=1:numFrames
my code is applied here.
So, I would like to know how to make this transition from prerecorded videos to real time video.
Your help in this so much appreciated!
I would suggest you to first verify whether you can perform acquisition + gesture recognition in real-time using your algorithm. for that, first read video frames in a loop and render or save them and compute the reading and rendering overhead of a single frame say t1. Also compute the time taken by your algorithm to process one image say t2. The throughput(no. of frames process per second) of your system will be
throughput = 1/(t1 + t2)
It is important to know how many frames you need to process a gesture. First, try to compute the minimum no. of images that you need to identify a gesture in a given time and then verify in real-time whether you can process the same no. of images in the same time.
Is it possible to play an audio file from the user's ipod library and have a callback occur whenever the player reaches a certain time point ? I need it to be very accurate, so simply using methods like currentPlaybackTime might not be enough because float equality is inaccurate. I could use the A - B < Epsilon float check, but is there a better, more accurate way of achieving this?
If you can target iOS 4.0 or hight, try using AVPlayer. Then you will be able to use
- (id)addBoundaryTimeObserverForTimes:(NSArray *)times queue:(dispatch_queue_t)queue usingBlock:(void (^)(void))block
which takes an array of NSValues for CMTimes and will run the contents of the block each time one of the boundary times is hit. (Beware of some behavior like, if you pause the audio file inside of the block, the callback will fire again when you unpause it).
Since CMTime is not a float, I think this will be more accurate than checking for the currentTime repeatedly.
I have a MPMoviePlayerController in my project.
Documentation says that next call:
moviePlayer.initialPlaybackTime = time;
starts at the closest key frame prior to the provided time.
Is it possible to start playing video from the specified time (not from the nearest key frame)?
No, it really isn't. Temporally compressed video streams can only generally start playback on a keyframe, as inter-frames depend on the keyframe for rendering. If seekability is important to you, consider making files with smaller keyframe intervals.