CONFIDENTIAL
DOC-USR-0030-12
___________________________________________________________________________________________
Z3 Technology, LLC
♦
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31
7.11
Tuning for Latency
For latency, the key parameters to work with are Maximum Delay and Number of B-frames.
Maximum Delay defines the number of milliseconds of buffering the encoder has to work with. The
higher this value, the more buffer it has to work with and the more time it has to “smooth things out”
for challenging content. However, a higher value also causes latency to increase accordingly. To
minimize latency, this value should be set to the lowest possible value. The lowest value Z3
recommends is 100. Note that lowering this value will also cause quality to degrade for challenging
content (because the encoder has fewer bits “over time” to work with). The tradeoff between
latency and quality through this parameter is left up to the user.
B-frames improve the quality of the picture, but they also increase the latency by 1 frame time. To
minimize latency, B-frames should be disabled (done by setting “Number of B-frames” to 0).
Figure 20 shows the suggested values for Maximum Delay and Number of B-frames for three common
use cases:
Maximum Delay
# of B-frames
Case 1: Highest Quality, Highest Latency
3000
2
Case 2: Good Quality, Standard Latency
2000
1
Case 3: Normal Quality, Lowest Latency
100
0
Figure 20 Tuning for Various Use Cases
RTP offers lower latency than UDP, so for the lowest latency you should use RTP.
If you are streaming to VLC, you can reduce latency on the decode side by adjusting the network caching
value. By default, this is set to 1000ms. You can lower this to as low as 200ms. To do this, go to the
following:
VLC
→
Tools
→
Preferences
→
Show Settings (ALL)
→
Input / Codecs
→
Network caching (ms)
