From VFXPedia

Contents 1 Preview Overview 1.1 RAM Cache Previews 1.2 File Sequence And Disk Previews 1.3 Flipbook Previews 1.3.1 Creating A Flipbook Preview 1.3.2 Removing A Flipbook Preview 1.3.3 Resizing Flipbooks 1.3.4 Saving Flipbooks 1.3.5 Memory Usage 1.4 AVI Previews 2 Final Renders 2.1 Starting A Final Render 2.2 Stopping A Final Render 2.3 Render Status And Statistics 2.4 Troubleshooting Renders 2.5 Memory Optimization 3 The Render Settings Dialog 3.1 Rendering Dialog And Options 3.1.1 High Quality 3.1.2 Motion Blur 3.1.3 Some/All 3.1.4 Use Network 3.1.5 Size 3.1.6 Frame Range 3.1.7 Shoot On 3.1.8 Configurations 3.1.9 Status 3.2 Bypassing The Render Settings Dialog 4 Queueing Multiple Flows To Render

Preview Overview

Since most composites happen over time, it is very important to be able to view a project or a selected clip at the intended frame rate, not just a single frame at a time. Although this can often be done by rendering the final output to disk, a full quality, full resolution render can be prohibitively slow for large composites.

Rendering a preview instead can be much faster, due to three main advantages:

• Previews need not render the whole comp. When creating a preview on a particular tool, only "upstream" tools that it depends on are rendered. This allows fast previewing of individual layers in your composite, for example.
• Previews can be rendered at reduced resolutions. A one-third (1:3) sized preview can be up to nine times faster than a full-size render.
• Previews do not need to be rendered in HiQ (full quality) mode. The effect of this varies for each tool, but many tools are significantly faster to render when quality is not an overriding factor.

When the intention is to evaluate an effect, a lower resolution Preview is often sufficient. Fusion offers several different ways to perform such previews.

RAM Cache Previews

When working with a composite, the frames rendered for interactive display are cached into memory, up to a preset memory limit. Priority is given to maintaining caches for tools that are currently viewed in a display. Other tools may also cache their result, depending on available memory and the time cost of the tool, among other factors.

Pressing the play forward or play backward buttons in the time ruler will attempt to play back the frames in the current render range at the rate configured in the frame format preferences. For example, if the frame format is set to NTSC D1, the frame rate attempted will be 29.97.

The composition will render only the tools that are required to produce the image from the tools that are currently viewed in the display views.

If a cache already exists for the tools currently being played, the composition will generally play at the full frame rate. The actual frame rate achieved during playback will be displayed in the status bar during playback. Frames without a cache will need to render first but, as they render, they will add themselves to the cache and, the next time they play through, it will be at the full frame rate.

This is not a preview in the technical sense of rendering a preview, but it does fulfill the same function in most cases and has the advantage of populating the cache used by Fusion to increase later interactive performance as well. A disadvantage is that that frames are cached at full depth, which can result in increased memory requirements when working with 16 bit or 32 bit pixel data, and can limit playback times and performance.

For more details on RAM caching, see the Caching And Memory Use chapter of this manual.

File Sequence And Disk Previews

File Sequence and Disk Previews are previews of file sequences on disk, as in the files used by a tool that has been cached to disk. A file sequence preview plays a series of files from disk as quickly as they can be loaded from disk and formatted for use in the display view.

Both loaders and savers, which are tools that refer to files stored on disk, are able to play these types of previews.

When a loader or saver is the selected tool in the flow, transport controls appear beneath the tool controls. Tools that have a pre-rendered or populated disk cache will also reveal transport controls when they are selected.

Clicking on any of the transport buttons will enable the file sequence playback. The left display view is normally used to display these previews, although the target display can be changed using the Preview Preferences>Display File Sequences menu.

The target frame rate is chosen from the frame format preferences but it can be changed using the RATE (FPS) control in the transports. The faster the drives are able to provide footage, the faster Fusion will be able to play the frames. A striped pair of IDE drives is often sufficient for full speed playback of NTSC- or PAL-sized frames, though disk fragmentation can limit this.

Frames played through file sequence playback are not spooled into the interactive cache.

While the file sequence playback is active, the display view cannot be used for normal image viewing. To disable the playback of the file sequence preview, de-select the tool that has enabled the file sequence preview to turn the display of the preview off.

Flipbook Previews

Flipbook Previews are stored entirely in RAM. These previews can play back smoothly at frame rates limited only by the bandwidth of the video hardware, which is typically as much as 100 fps. The frame rate is artificially limited by the rate configured in the frame format preferences.

Flipbooks are the fastest form of preview available. They have higher performance than RAM Cache playback, and can use less memory when working with 16 bit or 32 bit data. They also have the advantage of allowing fullscreen playback, with Fusion's interface entirely hidden.

When a flipbook preview is available, transport controls will appear beneath the tool controls.

Creating A Flipbook Preview

There are two ways to create a flipbook preview. Right-clicking on a tool and selecting Create>Play Preview from the tool's context menu will create a flipbook preview in the display view chosen.

A quicker method to create a flipbook is to hold down the Alt key, dragging the image into the display view. This will automatically create a flipbook in the display view. This method cannot be used to create previews to video display hardware, such as Leitch's Quattrus or NewTek's Video Toaster.

Removing A Flipbook Preview

The flipbook preview can be removed from the display view by right-clicking directly on the Preview and selecting Remove Preview from the flipbook's context menu.

Resizing Flipbooks

Scaling and panning a flipbook uses the same keyboard shortcuts and mouse commands used to scale and pan a tool that is displayed in the views.

Saving Flipbooks

A flipbook preview can be saved to disk for later use by right-clicking on the Preview and selecting Save As from the context menu. Flipbooks are saved to disk with the extension .FLB. They can be reloaded in a loader or display view that contain a flipbook at a later time for playback.

Memory Usage

Since flipbooks are stored in memory, they consume available memory used for image processing and tool caches. The amount of available memory determines the number of frames that can play back smoothly.

AVI Previews

In addition to the previews listed above, it is also possible to create previews using Video for Windows AVI files. AVI previews are rendered to disk so they do not have the memory limitations of flipbook previews.

AVI previews are well suited to previewing long frame ranges that would normally exceed available memory.

AVI previews are normally disabled in the preferences for flipbook previews. This option can be changed by selecting the AVI radio button in the Global>Preview preferences.

Final Renders

When all is said and done, the composite has to be rendered to disk. This is accomplished by adding a saver tool to the flow and pointing it to a directory on disk or over the network.

Any number of savers can be present at any point in a flow, making it easy to save intermediate composites, as well as final results in any resolution or format with a single pass.

Any tool that has a valid high-quality, full resolution frame in the memory or disk cache will not render. The cached result will be used instead.

Starting A Final Render

The green render button in the time ruler is used to start a final render. Alternately, use F12 as a keyboard shortcut to start a render, or select Start Render from the File menu at the top of the screen. When a render is started, the Render Settings dialog will appear.

This dialog, and its options, are described in the next section of this chapter. Once the options for the render are configured, click on the Start Render button on the dialog to initiate the actual render.

The dialog will disappear and the flow will begin to render. Fusion can continue to be used while the render progresses, opening compositions and creating new flows as needed, although performance will definitely be affected by the ongoing render.

View tools in the rendering flow to monitor the images as they are rendered. Any attempt to change controls or settings in the rendering composition will display a dialog asking if you would like to abort the current render.

To bypass the render settings dialog when starting a render, hold Shift down while clicking on the Start Render button.

Stopping A Final Render

When a render is in progress, the green Start Render button turns into a Stop Render button. To halt the render at the current frame, click the Stop Render button in the Time Ruler. A dialog will appear asking for confirmation.

A render can also be stopped by pressing the ESC (escape) key.

Render Status And Statistics

While a render is in progress, the status bar on the bottom right of the interface will display some statistics about the current render. The time taken to render the last frame, the average time per frame, the amount of time remaining, and the estimated time and day of completion are shown.

When the render is complete, final statistics for the time taken to render and the average time to render each frame will be displayed in a dialog box, as well as in the console.

Troubleshooting Renders

A render can fail to start or complete for several reasons. Generally, an error message in the console window will indicate a possible cause of the error. The following are common errors that can cause a render to fail.

• Missing frame in a file sequence on disk.
• Fusion could not find the footage for a loader used as a background input for a merge.
• Background input of a merge tool failed, perhaps running out of footage.
• Attempt to overwrite a DPS file with a new file of a different length.
• Saver path is invalid.
• Ran out of drive space on the destination.

Memory Optimization

The memory dialog in the preferences has two options that affect memory use during rendering. To access the memory preferences, select File. Open the Preferences tree for the flow and select the Memory node in the tree.

These options can be adjusted during a render to tune memory performance as a render progresses.

Simultaneous Branching

Enabling this checkbox will cause Fusion to render more than one branch of the flow at a time. Leaving this disabled can significantly reduce memory usage, which is why the option defaults to unchecked. Enabling this option can making the most efficient use of the system's processors on a multiprocessor system, provided enough memory is available. If the memory used during rendering exceeds physical memory, disable this checkbox.

Render 'X' Frames At Once

This slider is used to select the number of frames Fusion will render at once. Generally, the default value of 2 is sufficient. Increase the number of frames rendered at once if it appears that the CPUs are not being fully utilized during rendering. This is often caused by slow I/O when loading frames (usually over a network).

Increasing the number of frames at once allows Fusion to pre-buffer the next frames while the current one is still processing, smoothing out the spikes in processor usage caused by I/O access times. Decrease this value only if memory has run out and disabling Simultaneous Branching did not solve the problem.

The Render Settings Dialog

Rendering Dialog And Options

The Start Render dialog generally appears whenever the start render button is selected or whenever a preview render is initiated.

The dialog, as pictured below, provides control over the quality, range and size of the rendered frames. Features like step rendering, non-linear render ranges and low quality, proxied final renders are available from this dialog.

Final renders initiated from the Start Render button always default to the Final configuration, which renders every frame of the current render range at full quality, full size. These options are disabled unless the configuration is changed from Final.

High Quality

With the High Quality button selected, the rendered image will be produced with the best possible quality. De-selecting the High Quality button will cause Fusion to use faster, lower quality methods for merges, transforms, blurs and other operations.

Aside from producing fast proxies for use as previews, this function may also be useful when producing images that should not be sub-pixel positioned by the Merge tool.

Motion Blur

Deselecting the MB button bypasses motion blur on all tools when rendering. This can speed up renders and previews significantly, at the risk of reduced "fluidness" in the result.

Some/All

This option is similar to the Some/None/All option displayed in the Time Ruler. When the composition is set to Some, it will only render the tools that are required to produce output required by Saver tools in the flow. Orphaned branches in the composition will not render. This is a forced option for Fusion's final render settings.

The All option operates like previous versions of Fusion did when rendering, rendering all branches in the flow regardless of whether they terminate in a saver tool. There are very few situations where this would be required. A different configuration than Final must be configured to enable this option.

Use Network

Selecting this option causes Fusion to submit the render task to the Render Master configured in the network preferences. When selected, the Network Classes portion of the dialog will be enabled, allowing for the selection of the class (or group) of slaves used to render the flow.

Network rendering farms of computers can be used to produce flipbook and AVI previews, disk caches and final renders, as well as preview renders on supported hardware I/O devices.

For details on network rendering, please see the Network Rendering chapter in this manual.

Size

The Size dialog provides control over whether the full image is rendered or if the image is processed at the selected proxy resolution.

When rendering a flipbook preview, a rough estimate of the number of frames that can be held in memory without paging to disk is displayed to the right of each size option.

Frame Range

This dialog is used to set the range of frames rendered. It can accept a start and end Frame Range separated by two periods, individual frames separated by a comma, or a combination of both methods.

For example:

1..100

1,5,10

1..100, 110, 120, 121

Dashes (-) can also be used to separate the frame numbers in a range, such as 1-50. This notation, however, can cause confusion when rendering frames with a negative value (i.e. Fusion allows a render range of -50..100).

Shoot On

By default, Fusion will render every frame in the render range one at a time. For quick previews, it is often useful to render only one out of every few frames for an overview of the motion or effect. This technique is known as Shoot On. To perform a shoot on render, select the Step option in the Render Settings dialog and enter the step interval desired in the spinner box beneath the control.

When this option is enabled for a preview render, the frame rate of the preview will be modified so that playback of the preview will still take the same amount of time as it would if all of the frames had been rendered. For example, if the Shoot On option is set to a step of 5 frames for a RAM preview, and the render range is set to 1..100, the render will render frame 1, 5, 10, 15 until frame 100. When the preview is re-played, frame 1 will be held for five frames, frame 5 will be held for another 10 frames, and so on until the last frame is reached.

Configurations

It is possible to store the current render options for future use. Selecting the Add button will produce a dialog to allow the current render settings to be named. That name will then appear in the menu.

The render range is not stored in the configurations.

Status

The Status dialog displays any warnings and informational messages related to the render. For example, warnings for compositions that do not contain savers, or that have passed through tools, will appear here.

Bypassing The Render Settings Dialog

It is possible to skip or bypass the Render Settings Dialog by using whatever settings were last applied to the render. To bypass the render settings for a preview render, hold the Shift key down while Alt-dragging the tool into the display view. To bypass the render settings for a final render, hold the Shift key down while clicking on the Start Render button. To reverse this behavior so that the render settings dialog does not appear by default and will only be displayed if the Shift key is held down, use the option in the Preferences>General dialog.

Queueing Multiple Flows To Render

It is often desirable to queue up many flows to render one after another. This allows several flows to be rendered without waiting for each one to finish. A list of flows to render is called a Render Queue.

A queue can be created in Fusion using the render manager. To open the render manager, select File>Render Manager from the file menu, or press Ctrl-M on the keyboard.

For more information on the render manager, see the Network Rendering chapter.