This page last modified: 25 Apr 2011 12:14:43 PM.
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Video Cue
Video Cues allow you to display movies and still images on any screen attached to your computer. Video Cues are built on Quicktime, allowing them to use any media supported by Quicktime. This includes MOV, AVI, MPEG, JPG, PNG, etc.
A Pro Video license is required to reactivate Video Cues that have been saved to disk. In addition, the Video Cue requires a graphics card that supports
Quartz Extreme and Core Image. Please note: a compatible video card is a minimum requirement—not a guarantee of a specific performance level. QLab provides a wide range of video functionality, some of which demands a lot of processing power. Please see the section
Performance Tips to learn more about obtaining the best video performance.
All screens showing a Video Cue will be covered with a black background while the cues are playing on those screens. Screens where no video is playing show the normal desktop. As soon as all cues are stopped for a particular screen the desktop background will again show on that screen. Therefore if you wish the background to remain black for a screen you must make sure that at least one cue is running on that screen. It is advisable to set the Desktop background to a pure black image, just in case all cues are stopped unexpectedly.
If you wish to set a non-black background color simply create a Video Cue that uses a still image file for the custom background.
The mouse cursor will automatically be hidden if all screens are playing video. If one or more screens are showing the desktop the mouse will remain visible.
Obtaining the best video performance is a matter of balancing three principle factors:
- Hard drive speed / using multiple hard drives. A faster hard drive can supply raw video data more quickly. If you are using uncompressed video formats this can be especially important.
- CPU speed. The CPU decodes media data and performs other ancillary processing.
- Graphics card (GPU) speed. The graphics card performs all image processing of the video data in real time.
All three of these factors play a critical role during video playback, and your system performance can only be as strong as the weakest link in this list. Focusing on just one factor (e.g. focusing solely on the CPU) will not necessarily improve performance if the other factors are not also considered.
QLab performs all video operations on your graphics card, not your CPU. Live composition and fading of videos, the use of Core Image filters, and other such real-time processing all takes place on the GPU. In general, the fewer pixels the graphics card must process the smoother playback will be. Thus, if one card is having trouble driving two separate displays, try having it drive only one display. If the display resolution is high, try reducing the resolution. Fewer pixels means less work for your graphics card.
Each Video Cue achieves optimal performance if it is assigned to only a single screen. When assigned to only one screen, the video will be rendered directly to the video RAM (VRAM) for that screen. If a Video Cue is rendering across multiple screens it must first render the video to system RAM and then copy frames from RAM to VRAM in each separate graphics card. This extra copy operation is more expensive and increases CPU load.
Video cues that display still images will remain running until explicitly stopped. Even if they are no longer visible (for example, if another still image is covering them), they are loaded and consuming resources. It is important to stop old still image video cues that you do not need anymore, so that their resources can be released.
A Video Cue in full screen mode.
The Audio Patch of Video Cues functions the same way as the Patch of Audio Cues. It is used to assign the audio output device for the cue. Video Cues use the same patch routings as Audio Cues—the ones in the Audio Cue preferences.
The opacity specifies the initial visibility of the cue. For example, if you wish to fade in the cue you would set it to 0% so it would start out invisible. Then you would use an Animation Cue to fade it in to 100% opacity.
The order in which video frames are drawn is specified by the layer. A Video Cue with a higher numbered layer will be drawn over Video Cues with a lower numbered layer. You can use this, for example, to keep a mask image displayed over a series of other Video Cues.
Entering "top" means the Video Cue will be displayed over all other previously fired cues. The most recent Video Cue in the "top" layer is always displayed on top.
You can trim the head and tail of the video file with the start and end times. The reset buttons next to the text fields will reset the times to the natural start time (0) and the natural end time (the end of the file).
Use the looping checkbox to tell the Video Cue to play in an infinite loop.
By default, Video Cues will automatically stop themselves when they finish playing. If you want the last frame of the video to remain displayed when the video is complete, uncheck this box.
This setting does not apply to still images. Still images will always remain displayed until they are explicitly stopped by another cue.
The screens buttons allow you to select which screens your Video Cue will use. Note that the screen numbers are like audio patches: the actual map from number to physical device is set in the workspace preferences. So "Screen 1" can be any device connected to your computer, or no device at all. The actual device is set by how you have mapped "Screen 1" to a physical screen in the workspace preferences.
The tooltip for each screen button will show the name of the actual physical screen currently assigned to that number. Hold your mouse over the button for a moment to see the tooltip.
As noted in the
performance tips above, your Video Cue will perform optimally when it is assigned to only one screen.
When a Video Cue is in full screen mode it will be displayed on all the selected screens. You may optionally preserve the aspect ratio or stretch the video to completely fill the screens.
A Video Cue in custom geometry mode.
When a Video Cue is in custom geometry mode you can customize the translation, scale, and rotation of the video.
You can use
the stage interface to modify these parameters visually. Click anywhere on the stage and drag to adjust the translation. Click in the rotation bar handle and drag to adjust the rotation. Use the scroll wheel on the mouse to adjust the scale.
By default the X and Y scaled are locked to the same value. Click the lock button to toggle this setting on and off.
If you enter a negative value for the scale, QLab will flip the video image along that axis.
QLab 2 introduces a concept called the video stage. Instead of positioning your videos directly on the screens, you position them on the video stage. This allows you to more easily move a video workspace to a new computer with different screens.
The video stage GUI displays all the screens currently attached to your system. The screens selected for this cue are outlined in yellow. The video cue itself is displayed as a translucent yellow rectangle with a yellow border.
The light white crosshairs indicate the global origin of the stage. This origin is set in the Video Cue
preferences. This origin is useful if, for example, you want to display all your videos centered on a different screen. Instead of moving individual cue to the new screen you can just change the origin of the stage.
Click anywhere on the stage and drag to adjust the translation. Click in the rotation bar handle and drag to adjust the rotation. Use the scroll wheel on the mouse to adjust the scale.
QLab allows you to route the audio in your video files exactly like
the Levels of an Audio Cue. This audio is also in sample accurate sync, just like Audio Cues.
Just as with Audio Cues, the Trim tab allows you to adjust the final overall volume of each output channel. An example of their use would be if you have a series of fades operating on a single Video Cue: the series of fades may be just right except that you want the entire sequence to be slightly louder. Instead of having to adjust each end volume of each fade separately, you can simply go to the Trim tab and change the master volume up in one place.
The Trim can only be changed manually; they can not be changed by a Fade Cue.
QLab provides flexibility by allowing you to use a custom Quartz Composer file to render the video. By creating your own compositions, you can apply Core Image filters, render your video in 3D, and apply even more complex animations.
QLab will provide your Quartz Composition frames from the video file as it plays. To receive the frames your composition must publish an "Image" input port. Other ports you may publish include "xPosition", "yPosition", "Width", "Height", "Rotation", and "Opacity". (Opacity is passed as a color.)
The preferences panel for Video Cues allows you to map screen numbers to physical display devices.
To map a screen number to a physical device, click on the number you wish to map and drag the patch connector to the desired display device. You may have more than one screen number assigned to the same display device.
The Video Cue preferences also specify the global origin for the video stage. You may click and drag on the stage GUI to adjust the origin, or command-click to automatically center the origin on the clicked screen.
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