Flexible Transport of 3D Videos over Networks

Flexible Transport of 3-D Videos
Over Networks
Ahmed Hamza
Network Systems Lab
Simon Fraser University
July 15, 2013

Introduction
State of the Art
3D Video Representation
3D Video Coding
Transport Protocols
P2P Streaming
Adaptive 3D Video Streaming
Stereo Video
Multi-view Video
Case Study: DIOMEDES
Outline

In the near term, popular 3-D media will most likely be in the
form of stereoscopic and multi-view video.
Transmission of 3-D media, via broadcast or on-demand, to
end users with varying 3-D display terminals (e.g., TV, laptop,
and mobile devices) and bandwidths is one of the biggest
challenges to bring 3-D media to the home and mobile
devices.
Two main platforms for 3-D video delivery:
digital television (DTV) platforms
Internet Protocol (IP) platforms
Introduction

Platform for 3D Media Transport

IPTV
multimedia services delivered over IP-based managed
networks that provide the required level of quality of
service (QoS) and experience, security, interactivity, and
reliability
WebTV
services offered over Internet connections that support
best effort delivery with no QoS guarantees, making them
accessible anytime, anywhere as opposed to IPTV
IP-based Delivery Platforms

The DVB channel is constrained by the physical channel
bandwidth to allow transmitting multi-view video (MVV).
The IP platform is more flexible in terms of bandwidth but is
not reliable.
A more recent research direction is to consider a
combination of DVB and IP platforms to deliver MVV to
provide free-view TV/video experience.
Hybrid DTV-IP Approach

The most simple 3D video data representation
Each of the two captured views is presented to one of
the eyes
Can be multiplexed either spatially (passive) or
temporally (active)
Temporal multiplexing has the advantage of maintaining the full
resolution of each view
Disadvantage:
hardware representation dependency (acquisition process is
tailored to a specific type of displays, baseline distance between
the two cameras is fixed)
Stereoscopic Video

Multiplexing Stereo Video
Time Multiplexing
(double the frame rate)
Spatial Multiplexing
(half the resolution)

2D video signal along with geometry information of the scene
Video Plus Depth
texture
depth map

Multi-view Plus Depth (MVD)
Cam-0Cam-3Cam-6

Example
3D Image Warping
Ismaël Daribo and Hideo Saito, “A Novel Inpainting-Based Layered Depth Video for 3DTV,” IEEE
Transactions on Broadcasting, vol. 57, no. 2, June 2011

Layered Depth Video (LDV)
Main Layer
(central color view and depth map)
Enhancement Layer
(color and depth occlusions)
projected on central viewpoint

3-D video encoding depends on the transport option and raw
video format.
Simulcast encoding:
encode each view and/or depth map independently using a
scalable or non-scalable monocular video codec
enables streaming each view over separate channels
clients can request as many views as their 3-D displays require
Dependent encoding:
encode views using MVC to decrease the overall bit rate by
exploiting the inter-view redundancies
a special inter-view prediction structure must be employed to
enable view-scalable and view-selective adaptive streaming
Three-Dimensional Video Coding

Multi-view extension of H.264/AVC
Enables inter-view prediction
Prediction structure is simplified by restricting inter-
view prediction to anchor pictures only
Large disparity or different camera calibration affects
coding efficiency
Reference MVC software (JMVC)
temporal and view scalability
Multi-view Video Coding (MVC)

Independently code views and depth maps
Dependent encoding is also possible
Exploit correlation between texture and depth map
Examples:
sharing the texture video MVs with the depth map
utilizing inter-layer motion prediction tool in SVC
Multi-view Plus Depth Coding

Transmission Control Protocol (TCP)
may not be suitable for streaming live video with a strict
end-to-end delay constraint
lack of control on delay (retransmissions)
rapidly changing transmission rate (congestion control)
provides good performance when available network
bandwidth is about twice the maximum video rate (few
seconds pre-roll delay)
Transport Protocols

Datagram congestion control protocol (DCCP)
implements bidirectional unicast connections
both data and acknowledgements can flow in both directions
congestion-controlled, unreliable datagrams
congestion control mechanism selected at connection
startup
outperforms TCP under congestion when a video
streaming scenario is considered
Transport Protocols

Traditional client-server unicast streaming model is not
scalable by nature.
Advantage of P2P solutions
scalable media distribution (reduce the bandwidth requirement
of the server by utilizing the network capacity of the
clients/peers)
P2P solutions use overlay networks (data are redirected to
another peer by the application)
P2P Streaming

Efficient for delivering content from the server that is at
the top of the tree to peers that are connected to each
other in parent–child fashion.
Shortcomings:
ungraceful peer exit leads its descendants to starvation
replicating the content for feeding multiple trees leads to
redundancy within the network
Tree-Based Approach

Data are distributed over an unstructured network in
which each peer can connect to multiple peers.
Increased connectivity alleviates the problem of
ungraceful peer exit.
building multiple connections dynamically requires a
certain amount of time (initiation interval)
More suitable for applications that may tolerate some
initiation interval.
Example: BitTorrent
Mesh-Based Approach

A mechanism should exist to estimate the network
conditions so as to adapt the video rate accordingly, in
order to optimize the received video quality.
Estimation can be performed by
requesting receiver buffer occupancy status (to prevent
buffer underflow/overflow)
combining receiver buffer status with bandwidth
estimation
Adaptive Streaming

DCCP + TCP-friendly rate control (TFRC)
TFRC rate calculated by DCCP can be utilized by the sender
to estimate the available network rate
When the video is streamed over TCP, an average of the
transmission rate can be used to determine the
available network bandwidth
Basic method in DASH
Adaptive Streaming

Adapting video rate to available bandwidth depends on
the encoding characteristics of the views.
One or more views can be encoded multiple times with
varying bit rates, sender can switch between these
streams according to the network conditions
Similar to HTTP live streaming
Encoding views once with multiple layers using SVC and
switching between these layers
Real-time encoding with source rate control
Difficult with MVV
Video Rate Adaptation Methods

The behavior of the human visual system is another
paradigm for QoE-aware rate adaptation.
Exploit the suppression theory
human visual system (HVS) tolerates lack of high-
frequency components in one of the views
One of the views may be presented at a lower quality
without degrading the 3-D video perception.
Asymmetric quality allocation
Adaptive Stereoscopic
Video Streaming

Asymmetry can be achieved by scaling the quality in
one of the views (secondary view)
in spatial, signal-to-noise ratio (SNR) or temporal
dimensions
Questions
Which method should be used?
What is the level of asymmetry before observers start
noticing visible degradations?
Just Noticeable Distortion for
Asymmetric Stereo Coding

Just Noticeable Distortion for
Asymmetric Stereo Coding
Video Sequence Threshold PSNR (dB)
Parallax Barrier Polarized Projector
Adile 31.9 33.07
Iceberg 31.64 33.05
Flower Pot 31.19 33.2
Train Tunnel 31.74 32.88
Results show that the “just noticeable” threshold PSNR is
33 dB for the polarized projection display
31.5 dB for the parallax barrier display

Asymmetric Coding at a Fixed Rate Using MVC
Spatial asymmetry
using additional down-sampling steps in the encoding
process
Temporal asymmetry
skipping frames skipping from secondary view
SNR (quality) asymmetry
straightforward compared to other types of asymmetry
(encoding quality of a view depends on the quantization
parameter used)
Asymmetric Encoding
for Adaptive Streaming

Alternating views are coded at high and low quality.
Inter-view dependencies should be carefully
constructed (predict only from high-quality views).
Asymmetric MVC Coding

Scalable Asymmetric Coding Using SVC
It is possible to obtain spatial and/or quality scalable right
and left views if they are simulcast coded using the SVC
standard.
Two encoding options for achieving scalable asymmetric
stereoscopic video bitstreams when simulcast coding is
used:
encoding both views using SVC
encoding one view with SVC and the other with H.264/AVC
Asymmetric Encoding
for Adaptive Streaming

Can be done in two ways:
encode both views using SVC
base layer of each view is encoded with a quality ~32 dB
enhancement layers are encoded at the maximum quality
according to channel capacity
only one view (the first) is scalably encoded
second view is encoded using non-scalable H.264/AVC
When the available link capacity is high, the scalable coded
view (with the enhancement layer) becomes the high-quality
view.
Asymmetric Encoding
for Stereoscopic 3D Video

Asymmetric Encoding
for Stereoscopic 3D Video

Straightforward approach:
extend the concept of asymmetric coding to MVV streaming (for
relatively small number of views)
A more efficient (in terms of bandwidth consumption) and
flexible (in terms of number of views) approach:
streaming the MVD representation (includes view scalability)
View-selective encoding and interactive streaming of multi-
view video
requires computer vision methods for real-time head/gaze
tracking, can be used to limit the number of views transmitted
Adaptive Multi-view
Video Streaming

Discarding one view entirely and falling back to 2D video is
not a good choice.
switching from 3D to 2D results in significant viewing discomfort
With multi-view video (MVV) format, view scaling is a
possible option
missing view(s) may be outside of the user’s field of view or can
be replaced by an artificial view generated at the client side
Challenge
How to determine which view should be discarded for minimum
degradation in perceived quality?
View Scaling

Subjective tests to evaluate the performance of scaling
methods in terms of delivered QoE under different
network conditions.
5-view 3D display at 1920x1200 screen resolution
12 male and 4 female assessors (7 experts)
QoE-based Adaptation Policy
Description Symmetric Quality
Scaling
Asymmetric Quality
Scaling
View Scaling
Method # 1 2 3 4 5 6
Detail SNR Spatial SNR Spatial 3c+3d 2c+2d

Recommended adaptation policy:
QoE-based Adaptation Policy
State Method
1 All views transmitted at max quality
2 Asymmetric SNR scaling of intermediate views
3 Keep only edge views (+ depth) and use DIBR

Introduce quality difference between adjacent views.
View that are either transmitted or not are encoded with
H.264/AVC for high coding efficiency.
Views that may have different qualities to achieve
asymmetry are encoded using SVC.
Example:
For a five-view display, can perform this efficiently using SVC for
views 2 and 4.
Adaptation-ready Encoding

a) High link capacity (4.5 Mbps)
b) Low link capacity (3.3 Mbps)
c) Very Low capacity (2.1 Mbps)
MVV Adaptation Example

European project
Peer-assisted multi-view video broadcast
Scalable architecture that utilizes the upload capacity of
peers to assist distribution of up to 200 views and
associated 3-D audio
Main Idea:
DVB-T signal provides stereoscopic 3-D media as a
baseline
P2P distribution of remaining MVV views over IP to enable
immersive free-view TV experience
Case Study: Project DIOMEDES

Three modules:
3-D content server
master peers
3-D media streaming server
Peers that use both DVB
and IP channels synchronize
the received signals.
DIOMEDES Architecture

Adopts a mesh-based topology
Flat connections with no hierarchy
Adopts a divide-and-conquer approach and splits
content into equally sized chunks
Peers are of two types:
Seeders: have the whole content and upload chunks to
other peers
Leechers: have some missing chunks
BitTorrent Protocol

Chunk exchange is managed by two governing policies:
Rarest-first chunk scheduling
Determines the chunks to be requested
Favors chunks that least distributed
Tit-for-Tat
Determines which chunk requests are to be accepted
Sort neighbours based on their level of contribution
May deny requests from neighbours at lower ranks
Optimistic unchoking
BitTorrent Protocol

Chunk Mapping
Variable-size layered chunks
All chunks are self-decodable
Each chunk contains multiple GoPs
Adaptive video streaming
in 3D video streaming, rate adaptation is not
straightforward and may depend on external information
such as the user’s field of view, the encoding scheme, and
the display properties
Modifications to BitTorrent for
3D Video Streaming

P2P engine determines when to perform adaptation (discard/add a
stream).
Adaptation module determines which streams should be affected first.
3D Video Streaming

Chunk Downloading
ready-to-play buffer
buffer duration is a variable that provides feedback on the
overall content retrieval rate
3D Video Streaming

Chunk uploading
Request prioritization
Favor requests that belong to streams of high priority
Depth map streams should have the highest priority
because they are used to generate multiple views at the
client side.
Base and enhancement layers may be prioritized similar to
the case of 2D video streaming
3D Video Streaming

Full-resolution stereoscopic 3D video delivery
Full resolution source video is encoded as an
enhancement layer to the base stream in a frame-
compatible format that is transmitted over the DTV
channel.
The enhancement layer is transmitted to enable full
resolution 3D video for users with Internet access
Other Use Cases

Head tracking system for multi-view video delivery
head tracking system coupled with a stereoscopic display
View pairs change according to a user’s viewing position
if the available link capacity is low, only required video
streams are received, based on the feedback from the
head tracking device
increase efficiency of rapid view selection by using a
sparse camera arrangement and transmitting
corresponding depth maps
Other Use Cases

Digital TV platforms are not flexible to support multi-view
video (cannot provide sufficient bandwidth).
Three adaptive streaming solutions:
Asymmetric streaming
Streaming using MVD
Selective streaming
Combining adaptation methods with adaptive P2P video
streaming will provide a successful 3D video services solution
in the near future.
Streaming holographic 3D video over IP might be possible on
the long term.
Conclusions

Flexible Transport of 3-D Video Over Networks, Proceedings of the
IEEE, 2011
Peer-to-peer system design for adaptive 3D video streaming, IEEE
Communications Magazine, 2013
DIOMEDES: Content Aware and Adaptive Delivery of 3D Media
over P2P/IP and DVB-T2, Networked & Electronic Media (NEM)
Summit, 2011
Evaluation of Asymmetric Stereo Video Coding and Rate Scaling for
Adaptive 3D Video Streaming, IEEE Transactions on Broadcasting,
2011
References

Flexible Transport of 3D Videos over Networks

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