Traffic S Haping for Variable-Bit-Rate MPEG-2 Video

Traffic S Haping for Variable-Bit-Rate MPEG-2 Video

Traffic S haping for Variable-Bit-Rate MPEG-2 Video Il-Sung Lee Depart ment of Electrical Engineering McGill University Montréal, Canada August 1997 A thesis submitted to the Faculty of Graduate Studies and Research in partial Nfillment of the requirements for the degee of Master of Engineering. @ 1997 Il-Sung Lee National Library Bibliothèque nationale I+I du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395. rue Wellington Ottawa ON K1A ON4 Ottawa ON KIA ON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/i3xn, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fhm it Ni la thèse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Abstract As digital video services become more prominent, the strain that they place upon networks dlbecome more pronounced. The network of choice for carrying these transmissions will be the Broadband Integrated Senices Digital Network using the Asynchronous Transfer Mode (ATM) transmission protocol. In particular, ATM is well suited for handling variable-bit-rate (VBR) transmissions because it is capable of statistical mulitplexing. VBR coding is also advant ageous because it is conducive for producing consistent image quality. This thesis outlines the conversion of a software MPEG-2 video coder to operate as a VBR coder and then as a traffic shaping one. The rate controller for the traffic shaping coder is based on the Leaky Bucket policing algorithm to ensure conformity to the network traffic descriptors. First, comparisons are made between constant-bit-rate encoded sequences and their \BR counterparts. As expected, the VBR sequences possess superior aver- age peak signal to noise ratios (PSNFts) while maintaining a more consistent PSNR between frames. SecondLy, traffic shaped sequences are introduced for cornparison. Compared to the VBR case, these sequences exhibit a less erratic bit rate profile but also a lower average PSNR. However unlike the open-loop encoded data, the traffic shaped bit streams are not likely to encounter any network intervention when trans- mitted in any realistic network scenario. The effects of varying each network traffic descriptor (peak bit rate, sustained bit rate, and maximum burst size) are exarnined and the projected network-induced bit losses in the absence of traffic shaping are provided. Sommaire A mesure que les applications vidéo numériques prennent une place de plus en plus importante, le fardeau qu'elles mettent sur les réseaux de communication se fait de plus en plus lourd. Le réseau de choix pour acheminer ces données sera le Réseau Numérique à Intégration de SeMces (ISDN) à large bande utilisant le protocole de transmission à mode de transfert asynchrone (ATM). En particulier, le -4TM est bien adapté pour les transmissions à débit de données variable (VBR) puisqu'il permet le multiplexage statistique. Le codage VBR est aussi avantageux puisqu'il permet une qualité d7 images qui est plus constante. Cette thèse traite de la modification d'un codeur vidéo MPEG-2 pour agir comme codeur VBR et ensuite comme un codeur permettant de façonner le trafic. Le contrôle du trafic de ce dernier est basé sur la politique du seau percé ("leaky bucket") afin de se conformer aux descripteurs du trafic du réseau. Tout d'abord, des comparaisons sont faites entre des séquences vidéo codées à débit constant et à débit variable (VBR). Tel que prévu, les séquences codées VBR présentent un rapport signal à bruit (PSNR) moyen supérieur tout en conservant un PSNR plus consistant d'une trame à l'autre. Ensuite, des séquences façonnées pour le trafic sont présentées pour fins de comparaison. Comparées au cas VBR, ces séquences présentent un débit moins irrégulier mais aussi un PSNR moyen plus faible. Cependant, contrairement aux données codées en boucle ouverte, les flux de bits ("bit streams") façonnés pour le trafic n'auront probablement pas à subir une intervention du réseau lorsque transmis dans un scénario de réseau réaliste. Les effets de varier chaque descripteur du trafic de réseau ("peak bit rate", "sustained bit rate", "maxiumum burst size7') sont examinés et les pertes en terme de bits, prévisibles sur le réseau sont aussi fournies. Acknowledgments First and foremost, 1 would like to thank Dr. Éric Dubois for extending an invitation to supervise this project and introducing me to field of digital video coding. The volume of knowledge and skills gained throughout this project is immense and for this 1ni11 always be indebted. 1 have sincerely appreciated his guidance and patience. 1 must also acknowledge my appreciation for the financial assistance he, dong with the Canadian Institute for Telecommunications Research, has generously provided. Next, 1 wish to thank Dr. Nadia Baaziz for having developed the original INRS MPEG-2 coder, as well as other various utility software, used throughout the course of this research. 1 am grateful for her assistance in the early stages of my work and the patience she afforded me in discussing and explaining the uriclear and, at times, puzzling concepts surrounding the sohare and the MPEG standard. To INRS-Télécommunications, 1 offer my gratitude for providing truly excellent facilities and for lending me desk-space; a phone would have warranted my utmost gratitilde. To Dr. Maier Blostein, 1 thank him for his early guidance and willingness to be my supervisor at the University of McGill. Now he will no longer have to ask me "are you still here?" 1 would like to express my appreciation to Dr. Stephane Coulombe and Sonia Aissa for their assistance in translating the abstract into French, a feat, which if 1 had undertaken, might have brought me considerable ridicule. Also at INRS, 1 would like to sincerely thank Anthony Mancini for his frequent programming support and his assistance in handling the affairs of my thesis submission during my absence from Montréal. It is up to you to continue the tradition. 1would like to thank my family for their unbelievable support and understanding during rny academic life, especially during this latest chapter at McGill; it means more to me than 1can express. Finally, but certainly not least, my thanks go to the al1 good fiiends I have made at McGill and INRS. 1 would particularly like to mention a special group students with whom 1 have had the fortune to become roommates, and then good friends, when 1 first commenced my postgraduate studies. They have made my sojourn in Montréal enjoyable and mernorable and 1 owe them a lot. To Raymond Lee, thank you for graciously allowing me to stay with you during the last stretch of writing this thesis and, more importantly, for being a crue friend. To Emmy Choi, I will never forget your support, encouragement, and above all, friendship during this last year. -4ll will truiy be missed. Contents Abstract Sommaire Acknowledgments Contents List of Figures List of Tables 1 Introduction 2 Background 7 2.1 The MPEG-2 Video Encoding Standard - . - - . - 8 2.1.1 Ovenriew . - - . - . - . 9 2.1.2 Intra-frame coding . - - . - . 9 2.1.3 Inter-frame coding . 11 2.1.4 Profiles and levels . - . - . - 14 2.1.5 Video File Servers . - . 15 2.2 Constant and Variable-Bit-Rate Encoding . - . 17 2.2.1 Constant-Bit-Rate Encoding . - . - - . - 18 2.2.2 Variable-Bit-Rate Encoding . - . - 19 2.3 ATM and Packet Video . - - . - . 23 2.3.1 Overview . 24 a vi Contents 2.3.2 Network Policing ............ .. ........... 25 2.3.3 VBR Traffic and Statistical Multiplexing ............ 29 2.3.4 Issues Rrith Digital Video ..................... 30 Vaiable Bit Rate Video Encoding 33 3.1 The INRS MPEG-2 Encoder ....................... 33 3.1.1 Modifications to the Coder .................... 34 3.1.2 Fixed Quantization Scale Factor ................. 35 3.2 Experiments and Results ......................... 35 3.2.1 Achieving Constant Bit Rate .................. 37 3.2.2 Practical Considerations ..................... 38 3.2.3 Software and Hardware ...................... 40 3.2.4 Cornparison of Bit Rates ..................... 40 3.2.5 Comparison of PSNR ....................... 43 4 Bit Stream Trac Shaping 55 4.1 Ablotivation................................. 55 4.2 The Rate-Constrained Coder ....................... 57 4.2.1 The Traffic Shaper ........................ 57 4-22 The Modified Leaky Bucket ................... 60 4.2.3 The Quantizer Control ...................... 63 4.2.4 The Prebuffer and the Frame Recoder ............. 64 4.3 Limitations ................................ 65 4.4 Experiments and Results ......................... 65 4.4.1 Limiting the Peak Bit Rate ........... ........ 67 4.4.2 LimitingtheSustainedBitRate ................. 69 4.4.3 Adjusting the bfaximum Burst Size ............... il 4.4.4 Network Induced Losses ..................... 72 5 Conclusion 87 5.1 Thesis Summary ............................. 87 5.2 Future Work ................................ 91 A Definition

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