OccuRec


 
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Why a new file format?


There are a number of reasons for the creation of the new file format.
  • Analogue video runs at constant frame rate - PAL (25 fps) or NTSC (29.97 fps). One of the big improvements that OccuRec brings when using integrating video cameras is saving just a single frame for a full integration interval. When the user changes the integration rate of the camera during the recording with this the frame rate will also change. AVI files only allow a constant frame rate while AAV is not dependent on a frame rate.
  • In AAV format it is possible to implement bigger compression ratio while keeping the format lossless. This is because in AAV each pixel is represented by a single byte rather than 4 bytes. This however also means that AAV is a monochrome format and the user has to choose a way of conversion to monochrome pixels. For black and white video cameras it is recommended to use the R channel and scrap the G and B channels, while for colour video cameras it is recommended to use a GrayScale conversion from (R, G, B) to Y. The user can choose the option when connecting to a capture device.
  • With the continuing advances of the analogue video camera development, more cameras begin to offer computer control. With this the settings like Gamma and Gain will be known by the driver at the time of the recording and it will be nice if we can save them as well. AVI doesn't have any place where to store non-image data such as the Gamma and Gain of the camera. AAV offers any number of additional values related to a given video frame to be also recorded in the file. Furthermore when OccuRec reads the timestamp from IOTA-VTI it also saves the retrieved timing and GPS status separately in the AAV file allowing reduction software to be able to use this directly without having to 'read' the IOTA-VTI timestamp off the video frames during the reduction.
  • In the case of an unexpected problem during the recording, such as power outage for example, the standard AVI file will likely get corrupted and may become unreadable. The new AAV format is built in a way so it can be repaired if the recording has stopped in the middle of the frame. To repair a broken AAV file use the Tools -> ADV/AAV Tools -> Repair ADV/AAV File menu item in Tangra3.


Why using ADV like file format?


Making the AAV file format very similar to the ADV format used by the Astronomical Digital Video System (ADVS) was the most natural choice for me. Already having the source code to record in ADV format and the tools (Tangra3) to read and process an ADV file it was natural to make AAV simply an ADV file for 8 bit video data. With this however the state channel and system metadata had to be modified to fit better the usage of an analogue video camera and recorder that doesn't offer for example GPS coordinates of the observation.

What are the values recorded by OccuRec in the Status Channel of the AAV file?


Field Name Description Notes
StartFrame The frame id of the first frame included in the current integration period.  
EndFrame The frame id of the last frame included in the current integration period.  
IntegratedFrames The number of frames counted in the current integration period.  
SystemTime The computer system time at the time when the frame was saved in the AAV file.  
StartFrameTimestamp String representation of the VTI OSD of the start video field as recognized by the OCR engine. Only present if the OCR has been configured and is working.
EndFrameTimestamp String representation of the VTI OSD of the end video field as recognized by the OCR engine. Only present if the OCR has been configured and is working.
GPSTrackedSatellites The number of tracked satellites at the time of the VTI timing. Only present if the OCR has been configured and is working.
GPSAlmanacStatus The alamanc status at the time of the VTI timing. 0 = Waiting, 1 = Good. Only present if the OCR has been configured and is working.
GPSFixStatus The GPS Fix at the time of the VTI timing. 0 = Unknown, 1 = Internal Timekeeping, 2 = G Fix, 3 = P Fix. Only present if the OCR has been configured and is working.