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Playback command

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This command allows you to animate XY plots, drawing the plot data at a rate that you specify. Unlike the majority of DPlot's menu commands, the Playback command operates simultaneously on all open document windows that contain XY plots, with the limitations mentioned below. DPlot updates each plot drawing 30 times per second.


Time scaling used for the playback. If the X axis label contains "msec" or "millisec" DPlot assumes that the X axis units are milliseconds. Otherwise seconds are assumed: 1 unit on the X scale = 1 second. The actual playback duration will be the X extents of the data in the assumed units divided by the rate entry. For example, if the X axis label is "Time, milliseconds" and the extents of the plot are 1500 units (1.5 seconds), a rate of 0.1 gives a playback duration of 15 seconds.


This feature will only work on documents that use linear scaling on both the X and Y axes. There is no harm in having an open document that does not use linear scaling, but that document will not be animated.

Curves are drawn using the color palette for the currently active document, regardless of palette settings for other open documents. Symbols are not drawn. Curves are drawn using solid lines with the widths specified in the active document. Performance will benefit if you set the line widths to 1 pixel for all curves before using this command. You can force single pixel lines by setting the line widths to 0" on the Symbol/Line Styles dialog. The plot will be redrawn using the specified line style, color, and width when the playback dialog is closed.

The performance of this feature is of course dependent on the speed of your processor and the total number of points to draw in any one 1/30th second frame. If the playback jumps it may be necessary to decrease the rate entry. By way of example, a 1.44Ghz processor should easily handle up to 8 200Khz records played back at up to 20% of the data rate (40000 points per second x 8 curves). A P300, on the other hand, will choke on this load and the drawing will not be able to keep up with the desired framerate.

Start time

For multiple documents, DPlot will start redrawing each document so that the time scales are synchronized. For example, if rate=0.5 and document A starts at 0 seconds and document B starts at 3 seconds, the first line segment in document B will be drawn 6 seconds after the first line segment for document A.

Video playback

If you have an audio-video interleaved (AVI) file associated with your data, you can display the video frame-by-frame synchronized with the display of your data. Click the video button to select an AVI file. You will then be presented with an AVI Playback dialog with these entries:

File playback rate

This is the default framerate for the AVI file. This framerate is used by typical multimedia applications when playing back your file.

Actual recording rate

Enter the framerate used when your video was recorded. On entry this value is set to the same value used the last time you used this feature, or to the file playback rate the first time you use this function. Typically, explosive events are recorded at a very high framerate (2000-5000 fps), but then stored as an AVI file at a much slower rate, typically 30-60 fps. Unfortunately this information is not stored in the AVI file. You must be able to supply this value to have any hope of synchronizing the video playback with the rendering of your data.

First frame at t=

Enter the time value for the first video frame. When playing back your data, the video playback starts at this time. The preview window showing individual frames of the video should assist you in determining this value. Note: Some video formats, DivX and MPEG4 in particular, will be very sluggish on most systems when scrolling backward through the video. This is an inherent problem associated with the compression method rather than a problem with DPlot or AVIFIL32.DLL.

After accepting your input by clicking OK, a window showing the first video frame will be opened in the lower right corner of your screen. Although this window has no caption, you may move it by clicking anywhere within the window and dragging to the desired location.


Step forward, step back

If a video is used, the step forward and back buttons will advance/back up by one video frame. If no video is in use, the time step for each forward/back click is roughly equal to the extents of all plots divided by 100.

Video Example

You have several document windows open which depict pressure measurements from an explosive event. X=0 corresponds to the detonation. Your video was recorded at 2000 fps, and the detonation occurs in the 19th frame of the video. Eighteen frames before the detonation is 18/2000 = 0.009 seconds. Enter "2000" for file playback rate and "-0.009" for the first frame at t= entry.


This feature uses your Windows' AVIFIL32.DLL to interpret AVI files. Although your system may have the appropriate codec to display a particular file format, that format may not be supported by AVIFIL32. This is a Windows version-dependent limitation. For example, most Windows 95 systems will not be able to display AVI's with MPEG4 compression, while Windows 2000 and XP systems will.

The limitations mentioned above concerning data rate are of course also applicable here. If playing back the video results in poor performance with rendering your data, it may be necessary to use a smaller rate factor.

DPlot updates both the document windows and the video display 30 times per second, regardless of the video framerate. Depending on the values you've entered for actual recording rate and rate, this may result in video frames being skipped. If this is the case and it is important to view every video frame, use a smaller rate entry.



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