(SIGCOMM 2019) viewing of social live streams Optimizing...
Transcript of (SIGCOMM 2019) viewing of social live streams Optimizing...
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VantageOptimizing video upload for time-shifted
viewing of social live streams(SIGCOMM 2019)
Devdeep Ray, Jack Kosaian, Rashmi Vinayak, Srinivasan Seshan
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Social live video streaming (SLVS)
Server
Record
Upload
Real-time
delivery
Real-time deliveryDelayed
delivery
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Challenges in mobile social live streaming
Limitations of current techniques
Vantage:
Key ideas
Design and implementation
Evaluation3
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Bob
Alice
Network impairments tolerated by real-time viewers
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Charlie(Attending SIGCOMM during concert)
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Charlie
Delayed viewers also affected by network impairments
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Typical SLVS platforms today
Server
Record
Upload
Real-time
delivery
Real-time deliveryDelayed
delivery
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Video upload path is critical
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Available network bandwidth
Mobile streaming common
Significant bandwidth variation on upload path
The uploaded video is a baseline for all viewers
Downstream optimizations are limited by upload quality
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Qua
lity
Broadcast(Sports, News)
Conferencing(Hangouts, Skype)
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Viewing delay
Live video streaming today
"Real-time" latency constraintsVideo quality is secondary
Delay tolerantVideo quality is important
Social live streaming has both real time and delay-tolerant viewers for the same session
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Qua
lity
Broadcast(Sports, News)
Conferencing(Hangouts, Skype)
SLVS applications: WebRTC, RTMP
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Viewing delay
SLVS applications use conferencing techniques
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Qua
lity
Broadcast(Sports, News)
Conferencing(Hangouts, Skype)
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Viewing delay
SLVS applications
Today's solutions
SLVS today: Same video quality for all viewing delays
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Qua
lity
Broadcast(Sports, News)
Conferencing(Hangouts, Skype)
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Viewing delay
Goal: Better quality for delayed viewers
Goal: SLVS applications
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Challenges in mobile social live streaming
Limitations of current techniques
Vantage:
Key ideas
Design and implementation
Evaluation14
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Existing upload techniques: Real-time streaming
"Real-time" latency constraints
Bitrate closely matches available bandwidth
Sensitive to bandwidth variation
Conferencing(Skype, Hangouts, ..)
15Charlie
(Delayed)Bob
(Real-time)
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Existing upload techniques: Buffered streaming
Delay tolerant
Encode at ~ average bandwidth
Large sender-side buffers to absorb bandwidth variation
Higher video quality, no interactivity
Broadcasting(Entertainment, News, ..)
16Charlie
(Delayed)Bob
(Real-time)
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Existing upload techniques
Inadequate for SLVS:
Delayed + high quality video
OR
Interactive video17
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Challenges in mobile social live streaming
Limitations of current techniques
Vantage:
Key ideas
Design and implementation
Evaluation18
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Observation #1: Bandwidth is highly variable
Analyzed traces from the Mahimahi ** project
Significant variations observed, with extreme lows and highs
** Netravali, Ravi, et al. "Mahimahi: a lightweight toolkit for reproducible web measurement." ACM SIGCOMM Computer Communication Review 44.4 (2015): 129-130.
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Catering to multiple viewing delays
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Network is impaired: Use real-time strategy
When network recovers: Use less than capacity for real-time
Excess bandwidth used to repair past segments
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Viewing quality for different delays
21Bob Charlie
Real-time video bitrate
Delayed video bitrate
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Viewing quality for different delays
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Bob(Real-time)
Charlie(Delayed)
Why is Bob (real-time viewer) okay with this?
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Aside: Video quality metrics
Video bitrate != video quality
Vantage uses SSIM for measuring perceived video quality
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SSIM = 1.0 SSIM = 0.66
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Observation #2: Quality vs. Frame size is concave
Video encoded multiple times at different bitrates
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Size vs. SSIM plot for each frame
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Observation #2: Quality vs. Frame size is concave
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Observation #2: Quality vs. Frame size is concave
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Observation #2: Quality vs. Frame size is concave
Using high bandwidth to improve low quality frames very powerful!
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Challenges in mobile social live streaming
Limitations of current techniques
Vantage:
Key ideas
Design and implementation
Evaluation28
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Vantage: System architecture
Server
Record
Upload
Real-time
delivery
Real-time deliveryDelayed
delivery
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Vantage: Streamer Architecture
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Vantage: Key challenges
Real-time video stream bitrate
Enhancement frame selection
Video enhancement stream bitrate
Real-time decisions that optimize video quality for all viewing delays
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Input: 1. Bandwidth estimates2. Frame encoding stats
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Output: 1. Real-time bitrate2. Enhancement frames3. Enhancement bitrate
Input: 1. Bandwidth estimates2. Frame encoding stats
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Scheduling goals
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1. Constrain encoded bits to the available bandwidth2. Optimize video quality across multiple viewing delays
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Vantage scheduler
Mixed integer program (MIP) maximizes quality for multiple viewing delays
Periodically generates video encoding schedule
Key challenges:
Handling stale bandwidth estimates
Mapping frame sizes to quality
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Scheduler period trade-offs
Short time period
Accurate bandwidth estimates
Short sighted scheduling
Long time period
Stale bandwidth estimates
Long term optimal scheduling
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Handling stale network estimates
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Dual approach: Long term (MIP) + short term (Execution engine)
Vantage: MIP generates schedule every 2 seconds
Fallback strategy: Execution engine prioritizes real-time
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Vantage scheduler
Mixed integer program (MIP) maximizes quality for multiple viewing delays
Periodically generates video encoding schedule
Key challenges:
Handling stale bandwidth estimates
Mapping frame sizes to quality
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Frame size vs SSIM estimation
Frame size vs SSIM curve needed for optimization
Statistics from encoders drive estimation
Simple non-linear model: works well
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Size vs. SSIM plot for each frame
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Challenges in mobile social live streaming
Limitations of current techniques
Vantage:
Key ideas
Design and implementation
Evaluation41
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Vantage: Evaluation
Designed to work with existing congestion control protocols for real-time video
Emulated transport layer that provides network estimates from traces
Evaluation performed on different combinations of videos and network traces
Videos: Animated, talking head, drone footage
Network traces: LTE (Verizon, ATT), UMTS (T-Mobile) **
** Netravali, Ravi, et al. "Mahimahi: a lightweight toolkit for reproducible web measurement." ACM SIGCOMM Computer Communication Review 44.4 (2015): 129-130. 42
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Baseline: Real-time (conference style) streaming
All viewers affected by network variations
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Baseline: Buffered streaming
High quality for delayed viewing
Real-time viewing infeasible
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Vantage: Quality enhancing retransmissions
Real-time quality almost as good as real-time baselineReal-time baseline Vantage
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Vantage: Quality enhancing retransmissions
Real-time quality almost as good as real-time baselineReal-time baseline Vantage
46Delayed viewing quality significantly better!
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Other results in the paper
Multiple traces + videos, detailed results in paper
Varying delay distributions
Sensitivity analyses of optimizer period and bandwidth estimation error
Ablation studies comparing Vantage with naive solutions
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Results summary
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Up to 42.9% (average 19.9%) higher delayed video quality (Charlie = Happy)
At most 7% (average 3.3%) drop in real-time quality (Bob = Still Happy)
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Summary
SLVS applications present new and unique challenges
New paradigm of watching videos: Time-shifted viewing
Upload path variability is important to address
Vantage: Mitigates upload path variability to improve quality for time-shifted viewing
Thank you for listening!
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JackKosaian
RashmiVinayak
SrinivasanSeshan
DevdeepRay
Our research group