IRIS Eyz-On CVR, User Manual

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Eyz-On
CVR
User Guide
21214 45 Eyz-On
CVR
User Guide
Frame Rates and I Frames
Video is received from the imager at a rate of 30 frames per second (fps). In
normal circumstances MPEG4 and H.264 would compress this 30 fps into one
“I” frame followed by 29 “B” or “P” frames. Therefore, the minimum video clip
consists of an “I” frame followed by 29 smaller frames and this video clip would
represent 1 second of actual time. When the
Eyz-On is set up for a frame rate
less than 30 fps then the Eyz-On effectively discards the excess frames. Thus if
a frame rate of 15 fps is selected, then the Eyz-On discards every other frame
from the imager; if the frame rate is set for 3 fps, then the Eyz-On discards 9 out
of 10 frames. The reduction of the frame rate has a big impact on the encoded
video.
Since each encoded video clip has an “I” frame followed by 29 “B”
frames, the time resolution for the video clip is changed. Thus, if the Eyz-On is
set for 3 fps a video clip consisting of an “I” frame and 29 “B” frames represents
10 seconds of actual time.
Note: When the Motion Detection event is enabled the Eyz-On will
look for motion on frames from the imager that are not discarded due
to a frame rate setting less than 30 fps.
How MPEG4 and H.264 Events are Recorded
When Eyz-On is in the MPEG4 or H.264 mode the Eyz-On is continually
capturing and encoding the video image to internal memory. When the Eyz-On
detects that an event has happened and the Eyz-On is configured to record
images, the operation of the Eyz-On depends on if the system is currently
recording video or not. If the Eyz-On system is recording video for a prior event
or is currently recording due to a schedule time then it is assumed to be
currently in the record mode.
If the
Eyz-On system is currently recording video (in record mode), then the
event video will be saved starting with the next
“I” frame. If the
Eyz-On system
is not currently recording video (not in record mode), then the event video will be
saved starting with the previous
“I” frame.
Note the slight difference between the two modes. This is because the MPEG4
and
H.264 video must start with an “I” frame. If the frame rate is sufficiently
high, say 30 fps or 15 fps, this slight difference is not noticeable but with lower
frame rates of 3 fps the difference can be several seconds. Caution must be
exercised when using low frame rates with MPEG4 or H.264.
Length of Recorded Events
All MPEG4 or H.264 video clips must begin with an “I” frame, therefore the total
time length of the video recording segment will be determined by the frame rate
and the recording time specified for the event. Since a video clip must contain
an
“I” frame and a minimum number of “B” frames and the time required to