ADS Technologies USBAV-708 INSTANT VIDEOMPX, User Manual

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The maximum key-frame interval defines the
maximum number of consecutive frames that
may be a predicted type.
If
maximum key-frame interval frames have been
encoded since the last intra-frame, including of the
current frame, the current frame will be forced intra.
A fixed limit on the maximum interval between key-
frames is essential in ensuring that seek and error
recovery is prompt throughout the encoded video –
particularly for low-motion content that might otherwise
have a very low proportion of key-frames.
QUICK GUIDE
Maximum key-frame interval
More frequent key-frames can reduce the seek recovery time in media
players when the viewer attempts to skip to a specific point in the video. Due
to the nature of predicted frames a media player must decode every frame
from the nearest past key-frame until the seek target in order to resume
playback at the desired frame.
Reducing the maximum key-frame interval will cause an increase in the
proportion of key-frames to predicted frames throughout the video. Key-
frames are the most expensive in terms of bit-spend of all frame types and
using too many key-frames will starve the encoder of free bits causing the
rate control to return higher quantizers, in turn reducing the overall quality of
the video. Conversely, raising the maximum key-frame interval will cause a
decrease in the proportion of key-frames to predicted frames throughout the
video. Fewer key-frames translate to more free bits causing the rate control
to return lower quantizers, in turn increasing the overall quality of the video.
The maximum key-frame interval is limited to 60 frames when
Fastest
performance/quality mode is selected.
Maximum key-frame interval:
-key <frames>
Frames is the maximum interval between key-frames (intra-frames),
evaluated inclusive of the current frame.