CAMNET
System
Trick play
The smooth rate limit determines when playback must drop frames to maintain the faster playback rate. Given the typical 30 FPS of a recording, when the smooth rate limit is at its maximum of 3.0x, setting a playback rate of 3x results in 90 frames of video being shown every second. Since most LCD displays refresh at 60 Hz (60 times a second), one-third of the frames processed cannot be seen. This is wasted effort. If the original recording is at 20 FPS, 3.0x that is 60 frames a second.

When playing at a higher rate than this smooth rate limit CAMNET server drops all frames but I-frames. Generally, and well-advised for MPEG video, an I-frame is generated once per second, and all intervening frames are delta frames. At 30 FPS, that is one I-frame (larger size) followed by 29 delta frames (each a much smaller size than the I-frame). When playback rate exceeds the smooth rate limit, only the I-frames are processed and shown. For example, if the recording is at 30 FPS, and the playback rate were set to 8x, and this smooth rate limit were set to 3.0x, the true processing required is 8 I-frames per second. This is still showing the recording at 8x normal speed (8 seconds of recording are shown every second), but with only 8 frames processed over that second instead of 240 frames (30 x 8).

When viewing playback at high-speed, and then switching to a much lower playback rate, it can take several seconds for the new rate to take effect. The reason is there are still many seconds, perhaps minutes at very high speed, of video already in the system, ready to be processed and displayed. If this is taking too long, press Stop, then resume from the current time position (press Play).
Like Discard audio, Trick play (the smooth rate limit) is a client-side System panel state setting, stored in scp_L.txt.
[ camnet system, trick play ]