Make Video (avi)
DataView can make a video file (avi format) of a scrolling display of the main Chart view.
- Load the file swim.
The record shows extracellular recordings from the 1st roots of 3 adjacent ganglia in the abdominal ventral nerve cord of the crayfish. The rhythmic output reflects the swimmeret central pattern generator. We will first adjust the display characteristics to show some of the possibilities in making a video file.
- Select the View: Show axes, Show slider and Show grid menu commands. These are toggle commands that are active by default, so we have just switched them off.
- Select the View: Set size menu command, and enter 250 into the horizontal pixels box, and 200 into the vertical pixels box of the Display size dialog. This explicitly sets the size of the display.
- Select the Traces: Format command to open the Trace Format dialog.
- Click the light cyan colour from the Colour choice frame at the bottom of the dialog, and then click the Background colour button, which should turn light cyan.
- Click the OK button, and observe the main display (this rather garish colour scheme is not compulsory, it’s just to illustrate the selection process).
- Now select the File: Write video file (avi) menu command to open the Make Video dialog.
We want the video to scroll as smoothly as possible, so we will keep the frame rate at 30 fps, which is the normal maximum. If we wanted, we could slow down or speed up the display by entering a tape speed factor of less than or more than 1 respectively. This interacts with the scroll step parameter, and either could be adjusted. Note that changing this parameter has consequences for the audio output.
- Enter 5 into the duration box. This means that 5 seconds of the total recording will be incorporated into the video.
- In the audio section, click the stereo option.
- Leave Ch 1 as 1, but enter 3 into the Ch 2 box. This means that the left-hand audio channel will play from data channel 1 (the default), while the right-hand audio channel will play from data channel 3.
- Click the OK button, and then choose a filename.
- The Video compression dialog box appears next, with a drop-down list containing the available video codecs. This is generated internally by the operating system, based on codecs installed in the computer.
The Full Frames (Uncompressed) choice produces maximum quality, but can generate very large files. This is OK if the file is then going to be converted to another format (e.g. mp4 - see below) so that the original can be deleted, but otherwise one of the compressed formats is probably better. A good choice is usually the Cinepak codec, because although quite old, it is widely supported. You can set the compession level within the dialog, but I would leave it at 100%. Setting it to 10% produced a file that was only slightly smaller than 100%, and significantly de-sychronized the sound track.
- Click the OK button.
The display will now scroll through the recording, flashing horribly while it does so, while the video is constructed. IMPORTANT: do not switch to another task, or let another window obscure the display until the recording is finished. The video is constructed by capturing successive screen images, and if some other window comes in front of the display window, that will be captured too.
You should be able to play the video by opening it in the Windows Media Player, or something like the widely-available VLC media player.
When you play the video, you should here a stereo soundtrack that reflects the metachronal delay between the traces 1 and 3 in the recording.
Convert to MP4
If you want to place the video on a web page, or simply reduce the file size, the best option is to convert the avi file to mp4 format. This cannot be done directly in DataView, but there are plenty of free converters available on the web.