Exploiting the Power of H.264 Delivering Optimum Video Compression in Demanding System Environments

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1 A MARCH NETWORKS WHITEPAPER Delivering Optimum Video Compression in Demanding System Environments

2 Table of Contents Executive Summary...3 Introduction...3 Background...3 Improved Compression Performance...4 Dedicated H.264 Encoder...4 Implementation of H.264 in Edge Devices...5 Megapixel Cameras...5 Onboard Memory and Shadow Archiving...7 Multi-Streaming...7 Applications Exploiting H.264 Compression Technology...8 Conclusions...8 Glossary...9 About the Author...9 About March Networks...9 References...9 Appendix A H.264 Profiles Figures and Tables Figure 1 Relative Savings in Transmission Bandwidth and Storage... 4 Figure 2 Advanced Video Camera Architecture...5 Figure 3 Resolution Comparison and Corresponding Data Rates...5 Figure 4A Dynamic Streaming...6 Figure 4B Bandwidth Savings and Reduced Latency...6 Figure 5 Shadow Archive Architecture...7 Figure 6 I, B and P Frames in a Compressed Video Stream Figure 7 Removing Temporal and Spatial Redundancy in DCT Compression Engines Table 1 Comparison of Primary Compression Engines...3 Table 2 Storage Capacity of a 32GB SDHC Card Using H Table 3 Key Characteristics and Benefits of Codecs...7 Table 4 H.264 Profile

3 While H.264 compression technology itself has been well documented throughout the industry, innovative methods of utilizing its exceptional qualities are less apparent. Executive Summary H.264 video compression has rapidly established itself as the preferred video compression method, displacing a myriad of standard and proprietary schemes used during the past decade or longer. Many of the reasons for the industry adoption of H.264 are well understood, with the primary advantage being the ability to transmit high quality video at optimum file sizes. However, H.264 has the potential to enable much more, and through the unique implementation of hardware and software technologies, such as dedicated encoder ASICs and powerful system tools, exceptional levels of performance are achievable. Introduction March Networks has a long history of innovation in video compression technology, commencing with high quality H.263 encoders, followed by the introduction of MPEG-4 for codecs employing dynamic compression algorithms, to the more recent integration of H.264 compression with such advanced techniques as Shadow Archiving. While H.264 compression technology itself has been well documented throughout the industry, innovative methods of utilizing its exceptional qualities are less apparent. This paper briefly outlines the advantages of H.264, reviews possible implementations of the standard in edge devices, and examines key applications in megapixel cameras, multistreaming and Shadow Archiving where it is especially advantageous. Background Advances in video compression technology have introduced dramatic efficiencies in terms of system bandwidth and storage consumption. Video systems are able to adopt newer advances in hardware and software to deliver features that were previously limited by the available system infrastructure. H.264 compression is unquestionably a key enabler in this evolution. The three primary compression engines employed in video surveillance systems are M-JPEG, MPEG-4 and H.264. The following table illustrates their key features. Table 1 - Comparison of Primary Compression Engines Standard Compression Method Relative Bandwidth* Advantages M-JPEG Spatial, frame-by-frame 100% High quality; lower CPU burden MPEG-4, Part 2 Temporal, 4-vector motion compensated ~25% Good quality; moderate CPU burden H.264 (MPEG-4, Part 10), Main Profile Temporal, 16-vector motion compensated ~15% High quality; low bandwidth *M-JPEG requires the most bandwidth, which is fairly constant for each frame, whereas MPEG-4 and H.264 use temporal compression such that bandwidth consumption is more dependent on the level of motion present in the scene. 3

4 Figure 1 Relative Savings in Transmission Bandwidth and Storage Bandwidth 65 Mbps 6 Mbps M-JPEG 4 Mbps 2 Mbps MPEG-4 H Mbps 1 fps 5 fps 15 fps 30 fps Frame Rate Note: Actual bandwidth consumed depends largely on the resolution, scene complexity and level of motion present. Improved Compression Performance The improved performance of H.264 compression over its predecessors is largely attributable to two key factors: 1. Enhanced motion compensation techniques using ¼ pixel motion estimation and 16 motion vectors per macro block. For example, this compares with the use of only 4 vectors in MPEG-4, resulting in less effective compression. 2. An in-loop deblocking filter that significantly reduces blocking artifacts due to poor inter-correlation between the macro blocks, as well as motion compensated prediction. Interestingly, although H.264 is also known as MPEG-4 AVC Part 10, it is not interoperable with the earlier MPEG-4 Part 2 and uses quite distinct algorithms. H.264 is also unique in that it is organized in a profile hierarchy (see Appendix A) that enables product designers to select the parameters best suited to their application. For video surveillance applications, Baseline Profile is commonly implemented in system devices. However, Main Profile, adopted by March Networks, delivers superior video quality for the same bandwidth through the use of advanced prediction techniques. With a user trend toward real-time viewing at maximum frame rates, H.264 also has the added advantage of operating most efficiently at 30 fps, when there are smaller changes between frames. As a temporal compression engine, H.264 inserts key frames (I frames) at defined intervals and then simply transmits the difference between each frame in the intervening stream (B & P frames see Appendix A for more detail). Therefore, the smaller the change between frames, the less data there is to be processed and transmitted. Dedicated H.264 Encoder To offset the additional CPU burden of motion estimation in H.264 Main Profile, March Networks uses a low power, dedicated encoder ASIC, which enables the main processor The superior H.264 compression stream achieved using a dedicated encoder means that high image quality is maintained while recording at maximum frame rates. to work on other time-critical tasks in parallel, such as network transmission and video analytics see Figure 2. More importantly, this innovative architecture permits March Networks IP cameras and encoders to assume additional processing functions including Shadow Archiving, multi-streaming applications and megapixel camera technology. The superior H.264 compression stream achieved using a dedicated encoder means that high image quality is maintained while recording at maximum frame rates. 4

5 Figure 2 Advanced Video Camera Architecture using an Independent H.264 Encoder ASIC LENS IR Cut Filter MAIN CPU H.264 Encoder Video Processor SDHC Card YCbCr Resolution M-JPEG Encoder Multi- Streaming Progressive Scan Sensor CMOS or CCD Audio Codec Audio I/O This is in contrast to other types of edge devices that use the simpler, software-driven H.264 Baseline Profile, which delivers lower quality video, consumes more power and places a significant processing load on the main CPU. Implementation of H.264 in Edge Devices The introduction of H.264 compression, with its improved performance and lower cost of implementation, has enabled the broader adoption of a number of additional video technologies. The very combination of H.264 with such innovative design concepts makes these technologies far more compelling. Megapixel Cameras Only a few years ago, most video surveillance systems were set to record at CIF or 2CIF resolution, and indeed many still are. These limits were imposed on users largely through constraints Although progressive scan formats double the image data, the efficiency of H.264 compression actually minimizes the impact. in video storage and transmission bandwidth, as well as the camera technology available to leverage those resources. Progressive scan imaging technology, now common in IP cameras, doubled the pixel resolution, and consequently the size of each frame, and megapixel imagers doubled it again and beyond. Without H.264 compression, the high data transmission and storage rates would have been technically prohibitive. Although progressive scan formats double the image data, they exhibit much stronger vertical correlation, and therefore can be compressed to just 1.2 times that of interlaced formats using the efficiency of H.264 compression. Consequently, twice the vertical resolution is obtained for a relatively small 20% increase in bandwidth and storage. CIF 352x240 4CIF 704x480 Figure 3 Resolution Comparison and Corresponding Data Rates 1.3 Megapixel 1280x Megapixel 1600x Megapixel 2048x1536 Resolution Bandwidth* CIF 0.5 Mbps 4CIF 1.0 Mbps 1.3 MP 2.0 Mbps 2 MP 4.0 Mbps 3 MP 6.0 Mbps * Typical figures dependent on scene complexity and motion 5

6 Live streaming capabilities are important in a number of applications where real-time viewing is essential, such as in central monitoring stations. In the past, live viewing meant reduced frame rates, typically 1 4 fps, and low resolution with correspondingly poor quality. Even with H.264, high frame rates combined with high resolution on multiple cameras could impose limits were it not for an innovative March Networks feature that links display and transmission resolution see Figure 4A. Advanced encoders and cameras can change the video encoding in real-time depending on the image display size, removing redundant data and reducing the processing power required for decoding. The dynamic streaming example in Figure 4B reveals that quadrupling the information content from CIF to D1 results in only a doubling of the bandwidth. Figure 4A Dynamic Streaming, the set display resolution automatically adjusts the camera or encoder transmission data rate Edge Device IP Network Control Room VMS Server & Local Storage Staff set the display resolution for the monitor wall in the control room Simultaneously, the client adjusts the IP camera resolution to match that of the display resolution Only the required number of bits are transmitted and decoded to deliver the set display resolution SiteManager Client Figure 4B Bandwidth Savings and Reduced Latency Two of the Key Advantages of Dynamic Streaming An identical image at two different resolutions: D1 streaming at 1.4 Mbps, and CIF streaming at.51 Mbps. 6

7 Onboard Memory and Shadow Archiving The integration of solid state memory SDHC cards into edge devices has become a practical storage method through the adoption of H.264 compression. For example, 32GB capacity cards offer an economical method of storing video onboard cameras and encoders for an acceptable retention time of several hours or even several days, as calculated in Table 2. Table 2 Storage Capacity of a 32GB SDHC Card Using H.264 Compression Bit Rate (Mbps) Storage Time (Hours) Frame Rate / Resolution Equivalent p or 2 30 fps p or 1 30 fps p or 15 fps fps fps A tremendous advantage of onboard storage is to provide local backup, and thereby enhance distributed video redundancy. IP video systems can be vulnerable to interruptions caused by network faults, server failures or power outages, and the cost of mitigating these risks has traditionally been high. Through the intelligent application of onboard memory in IP cameras and encoders, video saved to an SD card can be mapped to a directory, known as the Shadow Archive, on a March Networks VMS server. Upon restoration of a network link, Shadow Archiving can automatically synchronize the video stored on the edge device with that of the VMS central storage according to pre-defined user policies. Access to the SD card video is also possible via the VMS central directory. Read more in our Shadow Archiving whitepaper. Multi-Streaming Multi-streaming is another system process that takes advantage of the high efficiency of H.264 compression. Cameras can leverage the different characteristics of video codecs to record and stream video in multiple formats to meet video quality, bandwidth and storage requirements. More sophisticated edge devices offer dual streaming, where each video data stream is transmitted simultaneously in real time depending on the application. Better still, an automated feedback loop can adjust each stream depending on available system resources such as bandwidth. Should the network infrastructure not support continuous broadband transmission, then either bandwidth limiting can be set by the administrator or streaming can be initiated only when built-in motion detection or a video analytic is triggered. Table 3 Key Characteristics and Benefits of Codecs Codec Characteristics Benefits H.264 MPEG-4 M-JPEG Low bandwidth; temporal compression Good quality video; temporal compression High quality video; spatial compression Recording at 15 fps or higher while keeping storage low Streaming or recording at moderate frame rates Streaming at frame rates of less than 15 fps in live monitoring applications. Predictable bandwidth and storage independent of motion. Figure 5 Shadow Archive Architecture SD Card Storage Edge Devices Control Room IP Network VMS Server & Central Storage plus Shadow Archive VMS Client 7

8 Applications Exploiting H.264 Compression Technology Consider two examples where multi-encoder cameras are deployed in an IP video surveillance system. Case Study 1 A retail store records video locally to a LANbased VMS and a central monitoring station monitors live video remotely. The LAN is 100BaseT, however the remote link is limited to 512 Kbps bandwidth. The decision is made to stream live video with M-JPEG at CIF resolution during normal business hours, increasing to full D1 on alarm, all while recording to the VMS server using H.264 compression on a second stream. This combination keeps the storage relatively low for recording at moderately high frame rates of 15 fps or more, and enables the streamed video to be restricted to the available bandwidth independent of the level of motion present. Conclusions H.264 is the most efficient compression algorithm for video quality and bandwidth efficiency and enables technology providers to develop exceptional applications that were previously impractical or prohibitive. H.264 video compression: Significantly enhances megapixel and HD camera technologies Enables higher frame rates or longer video retention for the same storage Makes dynamic multi-streaming more efficient Facilitates Shadow Archiving as a robust method of video backup Case Study 2 A bank s central monitoring station is connected via the WAN to hundreds of branches. Typically the bank views a single camera from each branch for routine security checks, but will switch to multiple cameras on alarm. Because the management software can automatically monitor the bandwidth used versus the bandwidth available, the administrator selects H.264 for a single camera with HD resolution, as well as H.264 for multiple cameras at a lower resolution. This combination enables the central monitoring station to maintain minimum frame rates for real-time viewing, even with multiple cameras selected. 8

9 Glossary ASIC...Application Specific Integrated Circuit AVC...Advanced Video Codec CODEC...Compressor/Decompressor CPU...Central Processing Unit DVR...Digital Video Recorder HD...High Definition NVR...Networked Video Recorder SD...Secure Digital SDHC...Secure Digital High Capacity SVC...Scalable Video Codec VMS...Video Management System About the Author Philip McDouall is Director of Solutions Marketing for March Networks, and holds a BSc(Eng) from the Royal Military Academy of Science, U.K. Phil spent the early part of his career in signals and communications in the British Army, and then in test and measurement engineering, before moving on to telecommunications. Phil has worked for March Networks since 2001, authoring a number of papers on video technology. He is a member of the American Public Transportation Association s CCTV standards committee, helping define video surveillance standards for the transportation industry. About March Networks March Networks (TSX:MN) is a global provider of intelligent IP video solutions. For close to a decade, the company has helped some of the world s largest commercial and government organizations transition from traditional CCTV to networked video surveillance used for advanced security, loss prevention and risk mitigation. VideoSphere, the company s enterprise-class video management portfolio, includes openplatform VMS software complemented by high-definition IP cameras, encoders, video analytics and recording platforms, as well as outstanding professional and managed services. March Networks systems are delivered through an extensive distribution and partner network and currently support over one million channels of video in more than 50 countries. References March Networks Whitepaper: Shadow Archiving in Video Surveillance Systems ; October 2009 March Networks News TechTip: Adaptive Compression Technology ; March 2006 March Networks News TechTip: From M-JPEG to H.264, what s right for the job? ; September 2009 March Networks TechBrief: MPEG-4 Video Compression: The Standardization Advantage ; February 2006 IQinVision: H.264 Considerations Part I; 2009 Anixter TechBrief: High-Quality Video with Low Bit Rate: The Promise of H.264 ; 2010 Wikipedia: H.264 Profiles; MPEG-4_AVC 9

10 Appendix A H.264 Profiles The H.264 profile hierarchy commenced with the three key profiles: Baseline, Main and Extended. Others have since been added to fill various, often niche, applications. The most commonly used profile in video surveillance is Baseline, with more advanced devices employing Main Profile. Key features of Main Profile over Baseline are: Use of B frames (see Table 4) Adaptive weighting for B and P frame prediction March Networks employs Main Profile, and while the processing overhead is slightly higher, the result is improved picture quality. The additional latency thereby introduced is compensated for by the use of a dedicated H.264 encoder ASIC, which reduces the computational burden on the main processor. DCT-based video compression techniques code the first image (key frame) of a video sequence (I), predict the macro blocks of subsequent frames (P), and create bi-directional prediction frames (B) by analyzing I and P frames see Figure 6 below. As a consequence, H.264 decoders are very efficient at image reconstruction. Profile Type Typical Applications H.264 Video Quality Bandwidth High Stereo Profile Two-view stereoscopic 3D video Highest High High 4:4:4 Predictive Profile (Hi444PP) Ultra High Quality broadcast applications that demand lossless video Highest High High 10 Profile (Hi10P) Professional applications that use interlaced video Medium Medium High Profile (HiP) Hi Definition and Megapixel Broadcast and disc storage applications. HD DVD and Blu-ray Disc, use HiP Medium Medium Extended Profile (XP) Mainstream consumer broadcast and storage applications that require high compression and higher reliability Medium Medium Main Profile (MP) Mainstream consumer broadcast and storage applications Medium Low Baseline Profile (BP) Low-cost applications that require additional error checking Lowest Low Constrained Baseline Profile (CBP) Table 4 - H.264 Profiles Low-cost applications like video conferencing and mobile applications Lowest Low Figure 6 I, B and P Frames in a Compressed Video Stream Frame Size Compressed Video Stream I Frames B Frames P Frame B Frames P Frame Time 10

11 Figure 7 shows the principle of temporal compression engines used in MPEG-4 and H.264 encoders. Where MPEG-4 uses 4 motion vectors, H.264 employs up to 16 motion vectors per macro block, each as small as 4x4 pixels, thereby improving video quality and compression efficiency. Figure 7 Removing Temporal and Spatial Redundancy in DCT Compression Engines RGB YCbCr Blocks Macro Blocks Remove Spatial Redundancy Remove Temporal Redundancy I B P Coding Quantization DCT 101, Motion Compensation North America Latin America Europe, Middle East and Africa Asia Pacific PN A March Networks EMEA Via Lavoratori Autobianchi, 1 Edificio Desio - Milano - ITALY Phone: Fax: March Networks Corporate Headquarters 303 Terry Fox Drive Ottawa, Ontario - CANADA K2K 3J1 Phone: Fax: A March Networks Company. All rights reserved. Information in this document is subject to change without notice. MARCH NETWORKS, VideoSphere, and the MARCH NETWORKS and VideoSphere logos are trademarks of March Networks Corporation. All other trademarks are the property of their respective owners.