HTTP-based Adaptive Streaming (HAS) plays a key role in over-the-top video streaming. It contributes towards reducing the rebuffering duration of video playout by adapting the video quality to the current network conditions. However, it incurs variations of video quality in a streaming session because of the throughput fluctuation, which impacts the user's Quality of Experience (QoE). Besides, many adaptive bitrate (ABR) algorithms choose the lowest-quality segments at the beginning of the streaming session to ramp up the playout buffer as soon as possible. Although this strategy decreases the startup time, the users can be annoyed as they have to watch a low-quality video initially. In this paper, we propose an efficient retransmission technique, namely H2BR, to replace low-quality segments being stored in the playout buffer with higher-quality versions by using features of HTTP/2 including (i) stream priority, (ii) server push, and (iii) stream termination. The experimental results show that H2BR helps users avoid watching low video quality during video playback and improves the user's QoE. H2BR can decrease by up to more than 70% the time when the users suffer the lowest-quality video as well as benefits the QoE by up to 13%.

1. H2BR: An HTTP/2-based Retransmission
Technique to Improve the QoE of Adaptive
Video Streaming
https://athena.itec.aau.at/ ◆ mailto: minh@itec.aau.at
Minh Nguyen, Christian Timmerer, Hermann Hellwagner

2. Contents
● Motivation
● Contributions
● Proposed Method H2BR
o HTTP/2’s Features
o Proposed Retransmission Technique H2BR
o Throughput Measurement
● Evaluation and Discussion
o Experimental Setup
o Performance Metrics
o Experimental Results
● Conclusions and Future Work
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3. Motivation
● Adaptive bitrate (ABR) algorithms choose the lowest-quality segments in the
startup phase.
● There are quality switches because of throughput fluctuations.
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4. Contributions
● An extension component at the client
○ Improve the quality of the first segments in the startup phase.
○ Eliminate the downward switches in the video quality.
● A throughput measurement when handling concurrent segments.
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5. Proposed Method H2BR
1. HTTP/2’s features
1.1 Server push
- Allowing multiple segments downloaded by one
request.
1.2 Stream priority
- Expressing how the client would prefer the
server to allocate resources when managing
concurrent streams.
1.3 Stream termination
- Terminating segment requests immediately.
Adaptive streaming over HTTP/1.1.
Adaptive streaming over HTTP/2 with server push.
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6. Proposed Method H2BR (cont’d)
2. Proposed Retransmission Technique H2BR
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Determine:
• The bitrate of retransmitted segments:
• The number of retransmitted segments (e.g., 2):
• The index of their first segment (e.g., i-2):
• The PRIORITY parameters of
RETRANSMISSION request ( ), and NEXT request ( )

7. Proposed Method H2BR (cont’d)
2. Proposed Retransmission Technique H2BR
Stream Priority
Server Push
High throughput, and
High buffer
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8. Proposed Method H2BR (cont’d)
2. Proposed Retransmission Technique H2BR
● To avoid stalls, retransmitted segments will be terminated if
○ Current buffer is less than a certain threshold, or
○ The remaining time for downloading retransmitted segments is less than a pre-
defined threshold.
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9. Proposed Method H2BR (cont’d)
3. Throughput Measurement
Segment size
Segment download time
Amount of data
Download period
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10. Evaluation and Discussion
1. Experimental Setup
● Two machines, one HTTP/2 server storing video content, one HTTP/2 client
○ Both are built on nghttp2 library.
○ Dummynet emulates a network trace.
● Video content
○ Big Buck Bunny: http://www.bigbuckbunny.org/index.php/download/
○ Length: 596 seconds
○ Segment duration: 1s, 2s, 4s, 6s
○ Quality: 20 versions
○ Resolution: 320x240, 480x360, 854x480, 1280x720, 1920x1080
● Compared method
○ SQUAD's retransmission
Dummynet
Throughput-based AGG
Buffer-based BBA
Hybrid SARA
Last throughput
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11. Evaluation and Discussion
2. Performance Metrics
● CDF of video quality: the cumulative distribution function of quality versions of
segments.
● Average video quality: the average quality level (levels 0-19) played out on
screen.
● Average switch step: the average of quality decrease.
● QoE: the overall quality score computed by ITU-T P.1203 QoE model mode 0.
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12. Evaluation and Discussion
3. Experimental Results
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CDF of video quality in an experimental run (segment duration = 4s)

13. Evaluation and Discussion
3. Experimental Results
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Average video quality

14. Evaluation and Discussion
3. Experimental Results
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Average switch step

15. Evaluation and Discussion
3. Experimental Results
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Overall QoE score based on the ITU-T P.1203 QoE model mode 0

16. Conclusions and Future Work
● Conclusions
○ An HTTP/2-based retransmission technique, namely H2BR
■ Working as an extension of ABR algorithms.
■ Improving the QoE up to 13%.
○ A throughput measurement when downloading concurrent segments.
● Future Work
○ Implementing H2BR for streaming scalable encoded videos over HTTP/3.
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17. Thank you for your attention
… questions, comments, etc. are welcome …
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