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General Settings
- What settings affect video quality?
- What settings affect latency?
- What is FEC and how is it used?
- What is the Shuffle setting for?
- What does the Jitter setting do?
- What is the difference between lost frames and recovered packets?
- Is there a way to remotely restart or shutdown a
Streambox Decoder or Encoder?
- What settings affect video quality?
These settings affect the final output quality:
- Resolution, from Full D1 down through ½ D1
- Bit rate, in megabits per second (Mbps) – higher bitrates generally deliver higher quality
- Increasing the buffer setting to compensate for high-motion video
- FEC settings, if applied
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- What settings affect latency?
Settings which are known to increase latency are:
- Increased variable bitrate (VBR) buffering
- Enabling FEC
- Enabling Shuffle
- Enabling Jitter
- Lower bitrate settings
- Audio codec type
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- What is FEC and how is it used?
It stands for Forward Error
Correction, and it’s a way of compensating for transient network conditions
to provide a more reliable stream by sending redundant packets along with
the data payload.
A setting of 1%
means that one FEC packet is sent for every one hundred data packets, and a 50%
setting means that one FEC packet is sent for every data packet. A clean
network path will not normally require FEC at all, while a typical setting
for an Encoder sharing a non-dedicated LAN could be 5-20% or more.
Please bear in mind that increasing FEC will take away from your video
bitrate to keep the overall bitrate below its maximum setting. For
example, a 5 Mbps stream with 20% FEC will deliver 4Mbps video and 1Mbps
FEC, while a 10% setting will deliver 4.5 Mbps video and .5 Mbps FEC.
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- What is the Shuffle setting for?
Shuffle is a way of overcoming sequential burst errors
by rearranging the order in which packet bursts are transmitted. This
increases the likelihood of the data arriving intact, in cases where
sequential burst errors are common.
Shuffle is only available when FEC is
enabled. Calculate the best shuffle setting using the following
formula:
Buffer/Jitter size in packets = FEC packets x Shuffle
size
EXAMPLE: 40 (FEC packets @ 2.5%) x 4 packets Shuffle = 160 or more
packets for Jitter buffer in Decoder. Be sure to create a relatively
large VBR buffer (3-10 seconds) with Shuffle enabled.
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- What does the Jitter setting do?
The Jitter setting is a way of increasing the buffer on the
decoder, which allows more time for packet reassembly at the decoder and
ensures smooth playback. This will affect latency, but is just another way
to overcome some of the more common network problems.
Note that this is different from the encoder buffer setting; jitter is a separate
buffer setting for the decoder. You could also increase buffering at the
encoder, which will have the same impact on both reliability and latency.
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- What is the difference between lost frames and recovered packets?
The Streambox devices are meant to work best over a fairly clean network
path, but this is not always available. As a result, packets can be lost or
delayed en route from the Encoder to the Decoder.
The ACT-L3 Video
Transport is a unidirectional system, and as such is intended for traffic to
flow from the Encoder to the Decoder. Unidirectional systems are a good
choice for reducing latency or for streaming through inherently
unidirectional systems, such as via satellite. However, they typically
provide no mechanisms for recovering lost or corrupt packets.
Corrupted frames can be
recovered and restored by enabling FEC. If the FEC setting is disabled
or is set too low for current network conditions, the
system cannot recover lost or corrupted frames and a noticeable error in playback
can occur. These are reported as lost frames, and the cumulative number of
lost frames (L=) and recovered packets (R=) can be monitored from the LCD
display on the front of the Decoder.
- How can I remotely restart or shutdown a Streambox Decoder or Encoder?
Login to the Streambox using Remote Desktop.
Use CTRL-ALT-END to bring up the Windows Security window.
Choose Shutdown.
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