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Adaptive Playout Scheduling Using Time-scale Modification
Yi Liang, Nikolaus FärberBernd Girod, Balaji Prabhakar
Yi Liang Adaptive Audio Playout
Outline
QoS concerns and tradeoffs Jitter adaptation as a playout scheduling scheme Packet scaling using improved time-scale
modification technique Loss concealment in compatible with adaptive
playout Performance comparison and audio demos
Yi Liang Adaptive Audio Playout
QoS Concerns at the Receiver
Delay Jitter
Delay Packet Loss
Obstructs proper reconstruction of voice packets at the receiver
Impairs interactivityof conversations
Impairs speech quality
Over best-effort network …
Yi Liang Adaptive Audio Playout
Playout Algorithm (1) - Fixed Deadline
Use buffer to absorb delay variations and playout voice packets at fixed deadline – jitter absorption
Voice packets received after deadline are discarded
Sender
Receiver
Playout
time
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8late loss
buffering delay
time
time
packetization time
Yi Liang Adaptive Audio Playout
Buffer Delay vs. Late Loss
late loss
buffering delay
Playout Jitter
Delay Packet Loss
Fixed playout deadline and jitter absorption:
The playout rate is constant The tradeoff is between
buffering delay and late loss
Yi Liang Adaptive Audio Playout
Playout Algorithms (2) - Adaptive Playout
Monitor delay variation and adapt playout time accordingly- jitter adaptation
Slow down playout when delay increases to avoid loss; speed up playout when delay decreases to reduce delay
Sender
Receiver
Playout
time
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
buffering delay
time
time
packetization time
slow down, speed up
Yi Liang Adaptive Audio Playout
Adaptive Playout and Jitter Adaptation
Adaptive playout and jitter adaptation Scaling of voiced packets in highly dynamic way Playout schedule set according to past delays
recorded Improved tradeoff between buffering delay and
late loss Playout rate is not constant
Playout Jitter
Delay Packet Loss
buffering delay
Yi Liang Adaptive Audio Playout
Packet Scaling (1)
Based on WSOLA [Verhelst 93]
Improved to scale short individual voice packets
“In-and-out black box operation”, no algorithmic delay, smooth transitions
Preserves pitch
output packet
1/20/1 2/3 3 4
input packet
pitchperiod
0 21 3 4
template segment
Yi Liang Adaptive Audio Playout
Packet Scaling (2) STD network delay= 20.9
msMax. jitter=112.0 ms
STD total delay= 10.5 msPackets scaled: 18.4 %Scaling ratio: 50% - 200%
DMOS: 4.5 DMOS scaling : degradation is 5 - inaudible 4 - audible but not annoying3 - slightly annoying 2 - annoying 1 - very annoying
Yi Liang Adaptive Audio Playout
Loss Concealment
Based on [Stenger 96] Using information from both sides, delay minimized to one
packet time Integrates nicely into system when adaptive playout is used 20% random packet loss:
Original: Loss: Concealed:
i-2 i-1 i+1 i+2
time
i-2 i+2
time
i lost
i-1 i+1
L L
2 L1.3 L
alignment found by correlation
Yi Liang Adaptive Audio Playout
Comparison of Different Algorithms
1. Method which uses fixed playout time throughout the whole session;
2. Method which estimates delay dynamically but only adjusts playout time during silence periods [Ramjee 94, Moon 98];
3. Method which dynamically estimates and adjusts playout time, and scales packets within talkspurts using time-scale modification.
Yi Liang Adaptive Audio Playout
Performance Comparison
Traces measured
between a host at
Stanford and hosts
in:
1) Chicago2) Germany3) MIT4) China
Yi Liang Adaptive Audio Playout
Overall Performance
Quality Score Excellent 5 Good 4 Fair 3 Poor 2 Bad 1
Buff. delay
Loss rate
MOS
Alg. 2 55 ms
10% 2.6
Alg. 3 4% 3.7
Original 4.4
Yi Liang Adaptive Audio Playout
Conclusions
Improved time-scale technique to work on individual packets with minimum delay
WSOLA based loss concealment integrates nicely into system
Adaptive playout and jitter adaptation significantly reduce buffering delay and late loss, which results in improved overall performance
Small playout rate variation can be traded for lower delay and lower loss rate
Playout scaling depends on audio scaling; scaling of individual packets is almost inaudible