Chapter 5. Media Layers

Intensity is used to fade the layer into, or out of, the output. As a layer’s intensity reduces, lower layers will show through.

Intensity also controls the audio volume for the layer.

Position controls where the centre of the layer appears in the output.|

Scale increases or reduces the size of the layer in the output.

Note that when magnified, low resolution content can look poor.

Rotation allows a layer to be rotated around its centre point. The centre point is controlled by Position.

Mirror and flip allow the layer to be flipped (reversed horizontally or vertically), mirrored (reflected about the centre line, horizontally or vertically), or both.

Stretch controls how the layer fills the screen. Every media file has an associated aspect ratio and this might not match the aspect ratio of the screen or projector. Stretch controls how the two aspect ratios are reconciled:

The R, G and B parameters allow the colour balance of the layer to be altered directly.

Colour effect, along with the associated R, G and B effect parameters, allows you to alter the colour of the layer in a number of ways. Full details are in the DMX parameter.

Here are some examples:

	A large number of effects are possible, and the best way to understand the parameters is to experiment. The ChamSys masks media folder (folder 3) includes an HSL colour chart and a TV test image. Both of these include solid colours and are very useful for testing out colour effects.

Blend controls how each layer is blended with the one below, in terms of colour and intensity. Blending takes place from the lowest layer upwards: Layer 2 blends with Layer 1, then Layer 3 blends with the result of 1 and 2, and so on.

Normally layers are simply blended by brightness and transparency: when a layer is completely opaque (full intensity, no mask), nothing can be seen through it. Normally, as a layer is faded, it becomes transparent so things below it start to show through. If a mask is applied, dark areas of the mask make the layer transparent, allowing layers beneath to show through.

These allow the media for the layer to be selected. If either are zero, the layer is switched off.

Start and end frame allow frame-wise control of which part of a clip is played. The default values are a start frame of zero and an end frame of 16777215 (2²⁴-1) which mean the whole file is to be used. If the end frame is less than the length of the clip, playback will stop (or loop) when the end frame is reached. Similarly playback can be started at any point in the file by setting the start frame.

To set the start and end frame accurately, you can use the First Frame or Last Frame Play Mode whilst changing the start or end frame values respectively.

To take complete control of playback speed (e.g. to bounce a clip between two points in time to a beat), use First Frame play mode, then apply a ramp effect to the start frame channel.

Although any values can be set in the DMX channels, the actual start frame will never exceed the end frame, nor will the end frame ever be earlier than the start frame. If you are using start and end frame to permanently edit a clip (i.e. you don’t change them or use a different part of the file in another cue), consider editing off-line since the resulting file will be smaller and using dedicated video editing software can produce better results. The values in the DMX channels refer directly to the frame numbers within the media. Frame numbers run continuously from 0 to the end of the file. The time that a frame number equates to depends on the frame rate of the file. For audio-only media the frame rate is 25 fps.

	Turning on the HUD for the layer being programmed will help since the start and end frame markers are shown on the media bar.

Use the speed parameter to control the speed and direction of media playback. Negative speeds cause playback in reverse. A speed of 0 stops playback (although see pause mode).

Up to 2 times normal speed, every frame is played. Bear in mind, therefore, that playing an HD clip x1.9 faster will nearly double the processing load for that layer. Above x2, frames are dropped to reduce the processing load. There is still an increased load for all but whole number multipliers: at x4.7, 3 out of every 4 frames are dropped, so the remaining load is x1.7.

Since there is an inherent loss of quality at high playback speeds (because the human brain can’t process the imagery so well), consider the quality and resolution of the source material carefully.

Play mode allows a movie clip to be played in a number of different ways:

5.13.12. Next frame

Advances the frame that is displayed, according to the speed parameter (i.e. direction and frame skipping for high speeds still apply), then automatically pauses. The mode must be changed away (e.g. to Pause), then back, before this mode can change the frame again.

	Pause can be used in conjunction with Next Frame (or other modes) to achieve more complex playback effects such as moving through a slide show.

Not implemented yet.

This parameter controls how opaque the mask is. If the opacity is full, the mask has complete control over the transparency of the layer. As the opacity is reduced, the mask has less effect: black areas that would have been completely transparent becomes less so, allowing less of the lower layers to show through. As opacity reduces to zero, the mask is effectively switched off.

These allow the mask for the layer to be selected. If either are zero, no mask is selected. If a non-image file is selected (i.e. a movie, audio or text file) the mask will have no effect.

This parameter allows the intensity of the mask to be inverted. This means that what would be fully transparent becomes fully opaque and vice-versa.

The same mask can be used in two layers, inverted in one layer, to produce synchronised masking effects, as shown in this example.

This allows the orientation of the mask to be controlled independently from that of the media file for the layer.

If anything other than this simple level of control is required, the mask must be used by itself in a different layer so that it can be independently positioned and rotated.

This parameter governs how the aspect ratio of the mask image is matched to that of the layer’s media. As far as the mask is concerned, the screen that it is being stretched to is actually the media file. If, for example, the media is appearing letter-boxed, setting mask stretch to Fill X & Y stretches the mask to the same extent as the media thereby altering the mask’s aspect ratio.

This parameter controls the audio level for the layer. A gain of zero turns off the audio playback. Note that the range is 0 to 10. For most purposes 0.5 to 2.0 will suffice. High gains can be used to boost very quiet clips.

This parameter is mainly intended to allows clips with different peak levels to be equalised.

This parameter allows the stereo image to be moved from left to right.

This parameter allows a variety of physical effects to be applied to the layer, independently from the Colour Effect. Full details are in the DMX parameter.