Technical Recommendation S. 10/07: Source Encoding of High Definition Mobile TV Services Version: 0.4 Date: November 29, 2007 Authors: M. Ries, M. Rupp Status: Final Page 1 / 7
Technical Recommendation S. 10/07 was revised by: Affiliation Contact person E-mail TU Wien/INTHFT Dipl. Ing. Michal Ries mries@nt.tuwien.ac.at Prof. Markus Rupp mrupp@nt.tuwien.ac.at Document History: Version Date Author Description 0.1 22.10.2007 Michal Ries First Draft Request for Comments 0.2 31.10.2007 Markus Rupp Review 0.3 14.11.2007 Michal Ries Review of Chap. 3 0.4 29.11.2007 Michal Ries Final Version Page 2 / 7
Table of Contents List of abbreviations 4 1. Summary 5 2. Introduction 5 3. Requirements for HD mobile TV 6 Bibliography 7 Page 3 / 7
List of abbreviations AVC CIF HD MOS PDA PQ PSNR SIF QCIF QoS SIF Advanced Video Coding Common Intermediate Format High Definition Mean Opinion Score Palmtop Perceived/Perceptual QoS Peak Signal-to-Noise Ratio Standard Interchange Format Quarter Common Intermediate Format Quality of Service Standard Interchange Format Page 4 / 7
1. Summary Provisioning of mobile TV services in suitable quality is gaining importance due to market and terminal development in recent years. The most challenging quality issue for provisioning of multimedia services is providing video streaming and broadcasting services in a required level of customer satisfaction. This required level of customer satisfaction is achieved with suitable combinations of codec and network settings for provided contents in order to allocate resources optimally from both the service provider as well as the user perspective. This recommendation is intended to define conditions for source encoding of video and audio streaming for High Definition mobile TV (HD mobile TV) services in order to ensure a high quality of this service at the user. 2. Introduction This recommendation describes condition for source encoding of audiovisual contents for HD mobile TV services. For the provisioning of video streaming services it is essential to provide a required level of customer satisfaction, given by the perceived audio and video streaming quality. It is therefore important for the service provider to choose the compression parameters so that they maximize the perceived quality of video content. Video compression improvement and higher processing and multimedia capabilities of end user terminals allow for providing video streaming while preserving perceptual quality. This is especially suitable for video applications in wireless networks. Mobile video services are characterized by limitations at the radio bearer and processing power of mobile terminals. These properties exclude provisioning of the video services with bitrates (BR) higher than 400kbps. The commonly used resolutions are Quarter Common Intermediate Format (QCIF, 176 144 pixels) for cell phones, Common Intermediate Format (CIF, 352 288 pixels) and Standard Interchange Format (SIF, 320 240 pixels) for data-cards and palmtops (PDA). The most suitable video coding standard for mobile broadcasting is H.264/AVC. Due to its significant improvement in video compression gain the newest video coding standard H.264/AVC allows to provide video streaming for low bit and frame rates while preserving perceptual quality. In the last years, several subjective test of subjective audio and video were performed [1, 2, 3]. The aim of these tests was to describe new usage scenarios [4] for mobile video services and to estimate a subjective quality for mobile video services [1, 2, 5, 6]. The recent achievements in this field show that the human visual perception of multimedia content is determined by the character of the observed sequence [5, 6]. The sequence character reflects audiovisual spatial and motion characteristics (content type, video motion features, spatial information) [5, 6]. Our proposed recommendations for source encoding of HD mobile TV services are according to these recent experiences. Page 5 / 7
3. Requirements for HD mobile TV The requirements for HD mobile TV are proposed for State of the Art mobile video delivery technology. The HD mobile TV is defined by the following requirements: - subjective quality, - objective video quality, - audio and video encoding parameters. The subjective quality is estimated according to ITU-T recommendations [7, 8]. The test method was absolute category rating (ACR) as it better imitates the real world streaming scenario. Test subjects evaluated the video quality using a five grade MOS scale (1-bad, 2-poor, 3-fair, 4-good, 5-excellent). In order to emulate real conditions of the mobile video service, all the sequences were displayed on an end user device 1. Mobile scenarios are strictly different in comparison with classical TV broadcasting services [4] or broadband IP-TV services. The mobile streaming contents provided mostly are news, soccer, cartoons, panorama for weather forecast or traffic news and video clip. According to our recent studies [5, 6] we recommend for HD mobile TV to achieve the upper quarter of a five grade Mean Opinion Score (MOS) scale (MOS 3,7 ). For the evaluation of objective video quality the most common objective video quality indicator Peak Signal-to-Noise Ratio (PSNR) is considered. PSNR reflects the coding degradation in spatial domain. MSE is the Mean Square Error evaluated as and where Orig(i, j) denotes the original value of the (i, j) pixel and Deg(i, j) is the received value of the (i, j) pixel for a given video frame. Furthermore, Orig refers to the original video frame and Deg to its encoded video frame. In order to provide a sufficient subjective video quality for all content types it is necessary to keep coding degradation of encoded video frames above 30 db. Moreover, the source encoding is defined by the following audio and video encoding parameters: Resolution: CIF (352 288), SIF (320 240) Video bitrate: 150 kbps Framerate: 10 fps Audio bitrate: 16 kbps Selected audio and video parameters should be equal or higher than the listed values above and simultaneously the final setting should fulfil the defined requirements for subjective and objective quality. 1 The ITU-T recommendations recommend a PC Monitor. Our own research showed clearly that this proposed method introduces a systematic difference between MOS results [9]. We therefore recommend at this singular point not to follow ITU-T recommendations but our own method. Page 6 / 7
Bibliography 1 M. Ries, R. Puglia, T. Tebaldi, O. Nemethova, M. Rupp, "Audivisual Quality Estimation for Mobile Streaming Services," In proc. of ISWCS, Siena, Italy; Sep. 2005. 2 M. Ries, O. Nemethova, M. Rupp, "Reference-Free Video Quality Metric for Mobile Streaming Applications," In proc. of International Symposium on DSP and Communication Systems, number 14-16, Sunshine Coast, Australia, Dec. 2005. 3 S. Winkler and F. Dufaux, Video Quality Evaluation for Mobile Applications In proc. of SPIE Conference on Visual Communications and Image Processing, number 593-603, Lugano, Switzerland, jul 2003. 4 O. Nemethova, M. Ries, A. Dantcheva, S. Fikar, M. Rupp, "Test Equipment of Time-Variant Subjective Perceptual Video Quality in Mobile Terminals," In proc. of IASTED InternationalConference on Human Computer Interaction, number 14-16, Phoenix, USA, Nov. 2005. 5 M. Ries, O. Nemethova, and M. Rupp. Motion Based Reference-Free Quality Estimation for H.264/AVC Video Streaming, In proc. of International Symposium on Wireless Pervasive Computing 2006, number 14-16, San Juan, Poerto Rico, Feb 2007. 6 M. Ries, C. Crespi, O. Nemethova, and M. Rupp, Content Based Reference- Free Quality Estimation for H.264/AVC Video Streaming, In proc. of IEEE Wireless Communication & Networking Conference, number 14-16, Honk Kong, Mar. 2007. 7 ITU-T Recommendation P.910, Subjective video quality assessment methods for multimedia applications, Sep. 1999. 8 ITU-T Recommendation P.911, Subjective audiovisual quality assessment methods for multimedia application, International Telecommunication Union, 1998. 9 O. Nemethova, M. Ries, E. Siffel, M. Rupp, Quality Assessment for H.264 Coded Low-Rate and low-resolution Video Sequences, Proc. of Conf. on Internet and Inf. Technologies (CIIT), St. Thomas, US Virgin Islands, pp. 136-140, 2004. Page 7 / 7