Extracting Light Curves from RunCam NightEagle Astro video files

The RunCam NightEagle Astro video camera presents two differences from most of the other cameras used for occultation data.  First, the sensor is a rolling readout CMOS sensor.  The rolling readout (or rolling shutter) aspect is very different from the interlaced CCD sensors in most of our other cameras.  With a rolling readout sensor, there are no true "field" exposures.  Assuming that the star images are only a few scanlines (pixels) wide, then the star is exposed for a full 1/30 second frame (1/25 sec in PAL mode).  So the data should be evaluated as FRAMES (not fields).  In addition, the NightEagle Astro has a misalignment issue with the video fields in the analog video output signal.  This analog video ouptut is divided into frames and each frame is further divided into two fields.  Normally, the data for each frame of an analog video output corresponds to the data from one "exposure" of the camera's sensors.  However, this is not true for the NightEagle Astro video output.  With this camera, the fields are shifted by one place.  To reconstruct the actual frame exposure from the CMOS sensor, we must shift the fields in the video output by one position. 


Step 1: Install avisynth
I am currently using the newer Avisynth+ but the older versions should work as well.  Here is a link to the releases page for Avisynth+

Releases · AviSynth/AviSynthPlus (github.com)

I installed the MSVC 2019 redistributable version ( the one with the *_vcredist.exe postfix).

Step 2: setup the script
Below is an AviSynth script which will "correct" the video output by shifting the fields one position.  Place this script (between the dashed lines) in a text file with the extension *.avs and change the "c:\tmp\myvideo.avi" file name to point to your video file. 

Step 3: Analyze the video in FRAME mode
Now you will open a corrected video file and analyze the video FRAMES (not fields) with your light curve extraction program (e.g. LiMovie, Tangra, PyMovie).  And you have two choices for how to proceed.

Option A:
Open the *.avs script file with your video program (LiMovie, Tangra, PyMovie) and start your analysis in FRAME mode to generate a light curve.

Option B:
Open the *.avs script file with VirtualDub and create a copy of your video file.  The copy of your video file will be "corrected" for the field shift issue and you can open this corrected video file in your video analysis program (e.g. LiMovie, Tangra, PyMovie) to generate a light curve.

Step 4: Review the Light Curve to extract timings
When reviewing the light curve, the data points will represent FRAMEs with a timing of 1/30 second (NTSC) between the data points. 

------------------start of avisynth script ---------------------
# This filter attempts to fixup the framing issue in a video file from the NightEagle Astro video camera
#   Given the following sequence of frames/fields
#    Frame 0: Field 1
#    Frame 0: Field 2
#    Frame 1: Field 1
#    Frame 2: Field 2
#   This filter generates the following NEW ordering by replacing Field 1 of a frame with Field 1 from the NEXT frame
#    New Frame 0: Field 1 = [Frame 1: Field 1]
#    New Frame 0: Field 2 = [Frame 0: Field 2]
#    New Frame 1: Field 1 = [Frame 2: Field 1]
#    New Frame 1: Field 2 = [Frame 1: Field 2]
#
DirectShowSource("c:\tmp\myvideo.avi",pixel_type="RGB")

Function MoveField1( clip c) {
    numFrames = Framecount(c)
   
    # trim to avoid funky half frames from frame grabbers
    #
    cT = Trim( c, 2, numFrames - 1)
    AssumeFrameBased( cT )

        # SeparateFields puts field 2 first in new stream
        #
    fAll = SeparateFields(cT)
    AssumeFieldBased( fAll )

    # grab field 1 with offset forward one frame
        #   and field 2 from start
    f1 = SelectEvery(fAll, 2, 3)
    f2 = SelectEvery(fAll, 2, 0)

    # combine fields to frame (with offset for field 1)
    #   f2 first since avisynth wants field 2 first
    #
    fNew = Interleave(f2, f1)

    AssumeFieldBased( fNew )
    cNew = Weave

    return( cNew )
}
------------ end of script ------------------