Current Products Legacy Products

Advanced LDMP in Detail

What each control means, what it changes, and how the controls relate

LDMP (Low-Delay Multi-Path) is Streambox’s two-way UDP transport for live video and audio. The decoder confirms received packets; LDMP can resend missing packets and distribute traffic across more than one network connection. The controls below balance bitrate, recovery tolerance, and latency.

Plain-language key: a packet is a small bundle of stream data. A packet is “in flight” after it has been sent and before the encoder receives confirmation that it arrived.

Capacity and packet-window controls

Control	Meaning and function	Effect or operating guidance
Target Bitrate	Maximum bitrate intended for newly produced video and audio. The variable-bitrate encoder may use less for simple material.	LDMP resends also consume network capacity. If the connection cannot carry both the production signal and recovery traffic, quality may fall and frames may be dropped.
IP Packet Size	Size of each UDP packet sent by the encoder. A packet is a small bundle of stream data.	Leave at 1392 bytes for normal Streambox Encoder operation unless Streambox Support directs otherwise.
CWND	Maximum number of sent packets that may be awaiting confirmation across all active network connections. Such packets are described as “in flight.”	Too small can prevent the intended bitrate from being sent before acknowledgements return. A larger value permits more unconfirmed packets; it does not force the encoder to send them.
CWND_Min	Lower boundary for the packet-window limit assigned to each active network connection.	It does not guarantee that this many packets will actually be in flight. The assigned per-connection limit may vary between CWND_Min and CWND_Max.
CWND_Max	Upper boundary for the packet-window limit assigned to each active network connection.	For a single connection, current field practice is to set CWND, CWND_Min, and CWND_Max equal. CWND_Max should not exceed the total CWND in that workflow.

Timing and recovery controls

Control	Meaning and function	Effect or operating guidance
ACK Timeout	Maximum time, in milliseconds, from sending a packet to receiving the decoder’s acknowledgement. If confirmation does not arrive in time, LDMP resends the packet.	Set above normal round-trip time (RTT) with margin for variation. More margin tolerates delay spikes; less margin reduces latency allowance but can cause unnecessary resends.
Send Timeout	How long an inadequately responding connection may remain in active media service before LDMP stops assigning it video/audio packets and changes it to ping/echo mode.	Shorter values identify a failed connection sooner. Longer values are less likely to remove a connection during a temporary interruption. A common wired starting range is 3000–4000 ms.
RTT Multiplier	Controls how much recovery LDMP attempts after a packet misses ACK Timeout.	Higher values give recovery more opportunity or time and may help a highly variable connection, but can increase latency. A value of 2 is a common stable-wired starting point; use the selected preset when possible.
Pre-buffer for delay	Tells the decoder how large to make its Jitter2 buffer—a waiting area for delayed or unevenly arriving packets.	More pre-buffer can improve tolerance of uneven delivery, but adds latency. Begin with the value supplied by the selected product-specific preset.
Shaping Percent	Advanced control associated with total transmitted bandwidth, including resent packets, in relation to Target Bitrate.	Current Streambox Encoder presets commonly use 0. Leave it at the product-specific preset value for normal operation.

Closely related controls

VBR Buffer: Encoder working buffer, measured in seconds. It provides time and data capacity for variable-rate compression. Larger values are more forgiving but add approximately the corresponding amount of encoder latency.

FEC: Forward Error Correction sends extra recovery data. LDMP already uses acknowledgement-based resends, so FEC is normally off with LDMP in current Streambox Encoder presets. Specialized workflows may differ.

Manual LDMP Settings: When selected, the entered LDMP values are used directly instead of product-specific preset values. For most users, a shipped Streambox Encoder preset is the safer starting point because it configures video, audio, buffering, and LDMP together.

How the main timing controls fit together

RTT → ACK Timeout → recovery → Send Timeout

RTT describes the actual round-trip delay. ACK Timeout decides when an individual packet is late enough to resend. RTT Multiplier affects the amount of recovery allowed after that event. Send Timeout decides when an inadequately responding connection stops carrying media and moves to LDMP ping/echo mode. Pre-buffer and the decoder’s jitter buffers provide additional tolerance at the cost of latency.