Preparing video records for analysis (Part 1)
All video analysis such as extracting event times will be done using LiMovie. LiMovie can open and process directly only standard AVI video files. However because different observers are generally using different equipment and have different ways of recording/grabbing the video files, it is possible that your video file cannot be directly loaded by LiMovie. This may happen if you have your video file saved in a different format. I've seen for example some equipment that records in MPG, MPEG or WMV formats.
In those cases we may have to use the help of the AviSynth software to load our video. Additionally it is possible that your video recording/grabbing software is using a special video encoding to save the video file and this encoding may not be available on a default Windows installation. In such a case you will have to be able to determine which codec you need and to know how to find it and install it. If you are not sure what a codec is, think about is as the algorithm used to save the video. Your grabber/recorder will know the algorithm and will be able to save the video, but if the algorithm is not installed in Windows your software (including LiMovie) will not be able to open the file.
But first lets start with something simpler.
Using AviSynth to load files into LiMovie
Let's try to use LiMovie and to open some of the occultation data files. To do this we first need to run LiMovie. If you have followed the installation instructions you should have a shortcut to LiMovie on your desktop. Double-click this shortcut to run LiMovie.
Once LiMovie has started up, if you haven't used it before, the first thing you will notice are the numerous buttons and options. Don't let them scare you as using LiMovie to extract the times is actually simple.
For now the buttons we are going to need are the ones highlighted in red on the above image. "AVI File Open" is used to open a file and the buttons in the second red section are used to play, stop, pause and step through the video. Press the "AVI File Open" button and navigate to the "Data/Lunar Grazes" folder from the WorkshopDVD and open record no 8: [8] 070213_ZC2644A.AVI
After you do this the gray screen of LiMovie will turn to white. This may look strange to you and before I used to think that this is an indication that there is something completely wrong with the video. However if you press the "Play" button you will see that the video plays correctly. Then the question is why this white screen?
Actually one or more "white frames" may appears sometimes at the beginning of the video with some USB video capturing devices and software when you are downloading the video from your camcorder or when you are recording directly to a computer. This is caused by different times of the audio and the video. What is happening is that the capturing device is recording audio but because there is no video yet that's why there are white frames at the beginning. A workaround would be capturing the video via FireWire interface rather than USB. A good software tool for capturing via FireWire is "Win DV" by Petr Mourek. Win DV is also included in this WorkshopDVD but you need to make sure your recorder/grabber has a Firewire interface.
Sometimes it is possible that even after you press "Play" in LiMovie all you see is this white screen and no video comes up at all. In such a case or when you want to analyze video files not in AVI format you will need the help of AviSynth to proceed.
AviSynth is a utility that cannot be "started" in the way LiMovie can be started. After it is installed on your machine it stays invisible and when any other program attempts to open a video file, AviSynth may start (again invisible to the user) and actually make this video file appear as a standard AVI.
To demonstrate AviSynth we are going to open the file [9] 070213_ZC2644BC.mpg, which is in MPG format, in LiMovie. The version of LiMovie on this DVD cannot open MPG files directly. The last beta of LiMovie can open some MPG files but not all of them so you may still need to use AviSynth with your MPG video files even when this beta is released.
To open this MPG file we need to write a very short and simple "script". For the purpose of this workshop we will store all script files under C:\LiMovie where you should have LiMovie installed.
Open this folder and create a new text file by going right click and choosing "New" -> "Text Document"
Then rename the file to 9.avs and press "Yes" when asked are you sure you want to rename it.
Then double-click on the file and it should be automatically opened in Notepad. Then copy the line below and paste it in the opened blank file:
DirectShowSource("E:\Data\Lunar Grazes\[9] 070213_ZC2644BC.mpg")
Then update the drive letter or the full path if necessary. If you are using the video samples from a DVD drive then check the letter of the DVD drive, if you are using an external hard-drive then check the letter of the hard-drive and update the "E:" in the above example if needed (for example with "D:" or "F:", etc.)
Once you are done save the file and go back to LiMovie and press the "Avi Open" button again. This time from the drop-down choose the second option - AviSynth File (*.avs)
Then navigate to your 9.avs file (probably in your C:\LiMovie) and press "Open" to open it. The video file is loaded and displayed correctly in LiMovie:
We learned how to ...
- Run LiMovie and how to open an AVI file
- Identify whether the file is opened correctly or not
- Create a simple AviSynth script that points to a video file
- Open an AviSynth script .avs file in LiMovie
 | Continue to the next part ... |
