29.8.3 Recording an Animation with ANSYS FLUENT

The steps for recording an animation using ANSYS FLUENT are as follows:

1.   Create an animation.

2.   Open a connection to the VTR controller.

3.   Set up your recording session.

4.   Check the picture quality.

5.   Make sure your tape is formatted (preblacked).

6.   Start the recording session.

Each step is described in detail in the following sections.

Create an Animation

When recording animations to video, you must first create your animation. It's also a good idea to play it back a couple times to make sure you are satisfied with it, and to save the animation key frame definitions to a file for later use (see Section  29.7.1).

When you are ready to record the animation, you can select Video in the Write/Record Format drop-down list found in the Animate dialog box. When you do so, the name of the Write... button will change to Record..., and you can click Record... to display the Video Control dialog box (Figure  29.8.3) used for video creation. This dialog box can also be displayed by selecting the Video Control... menu item in the Display pull-down menu.

Figure 29.8.3: The Video Control Dialog Box

Open a Connection to the VTR Controller

The steps for connecting to your VTR controller are as follows:

1.   Select the protocol used by your VTR controller using the Protocol drop-down list.

2.   Check the settings for your VTR controller by clicking on the Settings... button. For V-LAN, this will display the V-LAN Settings dialog box, and for MiniVAS, it will display the MiniVAS Settings dialog box.

3.   Select the RS-232 serial port used to connect the VTR controller to your computer. Usually, the serial port is identified by a file name such as /dev/ttyd1 for serial port 1, and /dev/ttyd2 for serial port 2. If this is the case on your system, you can simply set the value of Port #; otherwise, you can type a new file name in the Serial Port text entry. Make sure that you have the proper UNIX read/write permissions for the file.

4.   Open a connection to the VTR controller by clicking the Open button. If successful, a line will be printed out in the console window that reports the VTR controller protocol version and the VTR device ID.

Set Up Your Recording Session

Once you have established a connection to the VTR controller, you can set up your recording session. There are three types of recording sessions, as described below:

Preblack   is the process of formatting a tape by laying down a time code onto the tape. A tape must be formatted before any frame-accurate editing, including frame-by-frame animation, can be performed. During this process, one usually records a black video signal onto the tape as well, thus the name "preblack''. When you select this option, the current graphics window will be cleared to black. You can use the window to send your black video signal to the VTR.

Remember that when you preblack a previously formatted tape, a new time code will be written and any previously recorded video will be destroyed.

Live Action   allows you to record a live ANSYS FLUENT session which can be used for demonstration. This option requires your computer's video hardware to have a scan converter that will send the computer display image to your VTR system.

Animation   will play an animation that you have created, and record it onto your VTR system.

The Options... button in the Video Control dialog box is used to display the Animation Recording Options dialog box (Figure  29.8.4):

Figure 29.8.4: The Animation Recording Options Dialog Box

There are three parts to setting up your animation recording session:

1.   Select the recording source.

2.   Choose real-time or frame-by-frame recording.

3.   Set the video frame hold counts.

Select the Recording Source

There are two possible video sources that can be used for recording an animation: Screen and Picture. The choice of video source depends on what your video hardware/software provides. Here is a description of each:

Screen   can be used if your computer's video hardware can send all or a portion of the computer screen as a video signal to the VTR using a scan converter and associated software. With this option, you are responsible for setting up the scan converter and sending the video signal to the VTR.

Picture   instructs ANSYS FLUENT to create a picture of each frame of animation and send the picture file to the computer's video hardware using a system command. This option assumes that your computer's video system includes a frame buffer that can store an image and send it as a video signal to the video recording system.

When using the picture option, a shell script will be called that will send the picture file to the video frame buffer. The default setting is videocmd, which is a shell script that is included in your ANSYS FLUENT distribution. It is located in path /Fluent.Inc/bin, where path is the folder in which you have placed the release folder, Fluent.Inc. This shell script will execute your system's command to send an image file to the video frame buffer. The script videocmd is set up to call the SGI system command memtovid. If you have a different system, you must copy the shell script videocmd to a new file and modify it to perform the proper task on your system (see the comments in videocmd for details). You can specify the name of your shell script using the Video Command text entry in the Animation Recording Options dialog box.

In order to send a picture file of the proper format to the video frame buffer, you must set up the picture format using the Save Picture dialog box, which can be displayed by clicking the Picture Options... button in the Animation Recording Options dialog box. If you choose to perform a window dump to create the picture file, the default window dump command used will also be videocmd. You can change this setting to use your own command. After setting the picture options, click Apply instead of Save... in the Save Picture dialog box to apply the change.

Once you have set up the picture format and system command, you can test the configuration by sending the picture in the current graphics window to the video frame buffer. This is done by clicking on Preview in the Animation Recording Options dialog box. (Note that this is another way to send a black video signal to your VTR when you are preblacking a tape).

Choose Real-Time or Frame-By-Frame Recording

There are two methods for recording an animation: real-time and frame-by-frame. These methods are described below:

Real-Time   can be used if the animation playback speed is fast enough to provide a reasonably smooth animation in real-time. This is only available if the selected record source is Screen. In this mode, ANSYS FLUENT will simply turn VTR recording on, play the animation, then stop the recording.

Frame-By-Frame   is used to produce a higher-quality video animation by recording one frame at a time. For each animation frame, this method will 1) play the frame on the screen (and generate the picture file, if needed), 2) preroll the VTR, and 3) record the frame. If the animation has 50 frames, this procedure is repeated 50 times, i.e., 50 record passes are made. This is the recommended method, because the real-time playback of the animation will usually be too slow and choppy.

When recording in frame-by-frame mode, there is an optional setting called Frames/Pass, which can be used to try and speed up the frame-by-frame recording process. It specifies the number of animation frames recorded to tape per record pass. If the animation is long enough (200 frames or more), you can try setting this value to 2 or higher. For example, if you set this value to 2 for a 202-frame animation, it will record animation frame 1 during the first pass, frames 2 and 102 during the second pass, frames 3 and 103 during the third pass, and so on. This is possible only if the animation frames can be rendered in time to be inserted onto the tape during a record pass, so use this setting with caution.

Set the Video Frame Hold Counts

The video standard NTSC has a frame rate of 30 frames/sec (and the PAL standard has a rate of 25 frames/sec). At the NTSC rate, a 150-frame animation will take only 5 seconds to play. To stretch out the animation, you can record the same animation frame over 2 or more video frames. This is done by setting video frame hold counts for the beginning, middle, and end of the animation, using the Animation Recording Options dialog box controls described below:

Begin Hold   specifies the number of video frames to hold the first animation frame. It helps to hold the first frame for about 5 seconds (150 video frames for NTSC, or 125 for PAL) so that the viewer can get accustomed to the picture before the animation begins.

Frame Hold   specifies the number of video frames to hold each animation frame, other than the first and last. To slow down your recorded animation, try setting this value to 2 or 3.

End Hold   specifies the number of video frames to hold the last animation frame. You may want to hold the last animation frame for about 5 seconds to provide closure.

Check the Picture Quality

As described in Section  29.8.1, there are several sacrifices made when sending a computer image to video, including loss of color and resolution. Some steps can be taken to minimize the problem using the Picture Options dialog box (Figure  29.8.5). Display this dialog box by clicking the Picture... button in the Video Control dialog box.

Figure 29.8.5: The Picture Options Dialog Box

Color   Use these controls to ensure that all colors fall into the proper color space for your video device. Also, for best results, set the saturation and brightness levels to 80% or less.

Window Size   If you have a scan converter that converts a portion of the computer screen, you can set the graphics window to a particular pixel size to match the scan converter's window size. You can also create a margin around the picture in the window to keep unwanted parts of the screen (such as the window border) out of the video image.

Make Sure Your Tape is Formatted (Preblacked)

Before you can start the recording session, you need to make sure the tape has been preblacked with a time code or frame code. When you start with a brand new tape, you need to take time out and preblack the whole tape first. This can be done using the following steps:

1.   Rewind the tape to the beginning.

2.   Select a preblack recording session by clicking on the Preblack radio button in the Video Control dialog box.

3.   Send the VTR a black video signal using a scan converter or a picture by clicking on the Preview button in the Animation Recording Options dialog box.

4.   Click the Preblack button in the VTR Controls section of the Video Control dialog box to start the preblacking.

Start the Recording Session

Make sure you have the proper recording session selected. If you are recording an animation, the Animation radio button should be selected.

To start recording onto tape, you must first go to the "in point'' on tape where you want the recording to begin. With a blank tape, it is important to start at about 20 seconds into the tape, so the VTR has a chance to preroll up to the in point. You can use the VTR button controls to position the tape, but an easier way to go to a certain point is to type the time code or frame code in the Time or Frame counter and press the <Enter> key. For example, a time code of 00:02:36:07 is 2 minutes, 36 seconds, and 7 frames. In order to go to this position on the tape, you can enter the time code as 2:36:07, leaving out the leading zeros, or you can simply enter 23607, leaving out the leading zeros and colons.

Once your tape is at the start position for your recording session, click the Record button to start recording.