PSTR: Per-title encoding using Spatio-Temporal Resolutions

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Current per-title encoding schemes encode the same video content (or snippets/subsets thereof) at various bitrates and spatial resolutions to find an optimal bitrate ladder for each video content. Compared to traditional approaches, in which a predefined, content-agnostic (“fit-to-all”) encoding ladder is applied to all video contents, per-title encoding can result in (i) a significant decrease of storage and delivery costs and (ii) an increase in the Quality of Experience. In the current per-title encoding schemes, the bitrate ladder is optimized using only spatial resolutions, while we argue that with the emergence of high framerate videos, this principle can be extended to temporal resolutions as well. In this paper, we improve the per-title encoding for each content using spatio-temporal resolutions. Experimental results show that our proposed approach doubles the performance of bitrate saving by considering both temporal and spatial resolutions compared to considering only spatial resolutions.

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All rights reserved. ©2020
All rights reserved. ©2020
PSTR: Per-title encoding using Spatio-Temporal Resolutions
Hadi Amirpour, Christian Timmerer, and Mohammad Ghanbari
July 2021
1
IEEE International Conference on Multimedia & Expo (ICME)

All rights reserved. ©2020
● Introduction
● Per-title encoding
● High framerate videos
● PSTR
● Experimental results
● Conclusion
All rights reserved. ©2020
2

Introduction
In HAS:
● a video source is split into segments
● each segment is encoded at multiple bitrates
● compatibility with network condition is increased
3

4
Introduction
at higher bitrates:
● there are enough bits to allocate to all frames and their pixels
at lower bitrates:
● the lack of an adequate bitrate
● video frames are downscaled to get enough bitrate
● an upscaling artifact is added
● a trade-off is established between the perceived video quality of:
o the compressed video in its original resolution
o the video compressed at a lower resolution and its upscaled version

7
Per-title encoding
● it is based on the fact that in a given bitrate range, each resolution performs better than others in a
specific region and these regions are dependent on the video content.
● the bitrate ladder is optimized over:
o bitrate
o resolution

8
Per-title encoding
In per-title encoding:
● each video segment is encoded at multiple resolutions and bitrates
● all resolutions are upscaled to that of the original video
● scaled objective metrics are calculated
● a convex-hull is formed

9
Framerate
by increasing framerate:
● visual clarity is enhanced
● temporal artifacts such as flickering, stuttering, and motion blur are reduced
higher framerate videos require higher bitrates:
● a trade-off between framerate and compression efficiency is established

11
PSTR: Per-title encoding using Spatio-Temporal Resolutions
in PSTR, the video quality is considered as a function of three parameters:
● bitrate
● spatial resolution
● temporal resolution ( framerate)
QoE

12
PSTR: Per-title encoding using Spatio-Temporal Resolution

13
PSTR: Per-title encoding using Spatio-Temporal Resolution

17
Conclusion
• this paper derives an improved bitrate ladder for each content using both spatial and temporal
resolutions.
• experimental results show that the proposed method significantly improves the performance of the
bitrate saving by considering the temporal resolution in addition to the spatial resolution.
• the temporal resolution shows a similar impact on the bitrate saving as the spatial resolution
• our findings reveal in general (i) at lower bitrates using lower spatial resolution and framerates and
(ii) at higher bitrates using higher spatial resolution and framerates yield the best
• we note that we expect a significant increase of time-complexity by using both temporal and spatial
resolution for per-title encoding, which we aim to reduce as part of future work.

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