Video over USB By Ashwini Govindaraman, Cypress Semiconductor Corp. Not too long ago, high-definition TV changed the world forever by recalibrating the expectations that consumers have from their digital media experience. Content creation and consumption is now at a pivotal point where it is no longer enough to view only television shows and movies in stellar, high-definition quality. With over 600 million users now connected to some form of social media, user-generated content is a significant source of video traffic, with applications such as YouTube and Facebook becoming universal. As users continue to become increasingly mobile, they expect the same quality, performance and accessibility of content while on the go. They want to be able to watch vacation videos, the family webcam chat, or view a previously downloaded HDTV show with a faster and richer user experience. These multiple trends call for a convergence towards a common interface that is easy to use, portable, and flexible enough to provide a connectivity link for all types of media across a variety of applications. USB immediately comes to mind as one of the most user-friendly and universal connectivity options. With the evolution to USB3.0, this interface now provides a 5 Gbps data rate, which further strengthens its case as the video connectivity interface of choice. This article discusses the role USB3.0 can play in the video transport domain and compares it with two main interfaces that are also well-positioned to succeed: HDMI and DisplayPort. All three technologies have merits that compel their use in the digital living room as well in the PC and mobile realms. Why Video over USB? USB3.0 provides for a signaling rate of 5Gbps over a dual-simplex differential signaling interface. This high bandwidth capability makes it an ideal choice for video transport. Accounting for the overhead due to the 8b/10b encoding, the raw throughput over USB3.0 is about 500MBps enabling reliable transport of 1080p video at 120Hz refresh rate. (The bandwidth requirement for a 1920x1080p HDTV at a refresh rate of 120Hz and 10bit data is about 2.5Gbps. The bandwidth requirement for other video applications such as webcam to PC connectivity is typically lower as they typically require only 30fps.) Like USB2.0, the USB3.0 protocol supports bulk and isochronous data transfers. The type of transfer may be selected based on the application requirements. Isochronous transfers offer deterministic bandwidth with a potential accuracy tradeoff and are typically used for video streaming applications such as webcams. The high bandwidth of USB3.0 is further enhanced by the use of the Streams model introduced in the new protocol. This model enables multiple streams of data to be transported to and from bulk endpoints over a single physical USB3.0 interface. Different content can be displayed on different devices by sending multiple streams of data from a source, which are then routed to the corresponding device by a USB hub. Since the USB interface is agnostic to the actual data being transferred, USB3.0 can transport both uncompressed and compressed video. This flexibility allows USB3.0 to be the interface of choice for productivity applications, HD video playback, and many other applications such as sideloading videos from a PC to a mobile device or video streaming over a webcam (see Figure 1). Audio can also be supported, which puts USB on par with other interfaces such as HDMI and DisplayPort. Furthermore, enhanced power management techniques have been introduced to USB3.0, which along with the ability to transport compressed video (see Figure 2), allow for the careful optimization of power consumption in mobile devices. Due to the clear cost advantages of compression, most 2D and 3D content is now distributed in compressed formats over optical media or high speed internet. For example, the very popular Blu-ray is a compressed format. Interesting usage models are arising, such as connecting a cellphone or netbook/tablet to a monitor or several larger displays (see Figure 3). Gaming consoles connecting to the living room TV can all be enabled by the existing USB ecosystem without making any changes. Adoption of USB 3.0 in these segments would greatly enhance these use cases while maintaining the ease of use. Video over USB Page 1 of 7
Adoption and Ease of Use USB already ranks high in terms of consumer adoption and familiarity. It is easy to imagine the same plug-and-play connectivity interface being extended to media-rich applications such as downloading HD video from a PC to a mobile device, connecting a PC to multiple display monitors, and other scenarios. In addition, the same USB cable can be used to charge the USB device as well. Despite the advantages that USB has in terms of ease of use, bandwidth for supporting HD formats and a large installed base, it does suffer from the fact that there are incumbent interfaces that are well established in the media room. We will look into two main interfaces that have a stronghold in the living room and what benefits they offer. Uncompressed Video Transport over USB Video Chat Application Figure 1: Webcam connected to HDTV HD TV HD Player HD Compressed Content (eg. Blu-ray) Decoder Transmitter Uncompressed Video Receiver Display Video over USB Page 2 of 7
Figure 2: Uncompressed/Compressed HD Video Playback Multiple Streams Transported over USB Figure 3: PC Connected to Multiple Display Devices High Definition Multimedia Interface (HDMI) As the name suggests, HDMI is a standard for connecting high-definition products and is an all-digital interface. On a single connection, HDMI supports uncompressed video transfers in any format including HD, up to 8 channels of uncompressed audio, and a CEC (Consumer Electronics Control) connection. HDMI is also backwards compatible with DVI (Digital Visual Interface). It does provide ease of use and quality benefits in the living room. Key features and benefits that HDMI provides include: Support for the majority of video/audio formats HDMI transmits all formats of digital audio and video through a single cable, replacing as many as thirteen older cables and eliminating cable clutter. HDMI simplifies hooking up other devices to a home theater system: PCs, gaming consoles, and video cameras can all be connected with the same one-plug convenience. Video over USB Page 3 of 7
The HDMI architecture makes it easy to install or upgrade an all-digital home entertainment system as all HDMI versions are backward-compatible with previous versions. Bandwidth HDMI provides a bandwidth capacity of up to 10.2 Gbps, more than twice the bandwidth needed to transmit an uncompressed 1080p signal. This means better looking movies, faster gaming, and a richer audio for consumers. HDMI s bandwidth also means it is future-ready for emerging technologies such as 3D movies, higher resolution gaming, and support for higher resolutions (higher than 1080p), like 1440p or Quad HD. It would also allow for faster refresh rates such as 120Hz and deeper color, taking the HDTV palette from millions to trillions of colors. Other Auxiliary Functions HDMI is a "smart" two-way connection which allows devices to communicate and interact with each other to improve the overall home theater experience. Devices connected using HDMI have the ability to scan each other s capabilities and automatically configure certain settings. For example, an HDTV and Blu Ray player can auto-negotiate settings like resolution and aspect ratio to correctly match the format of incoming content to the highest capabilities of the HDTV. Consumer Electronics Control (CEC) provides for integrated, "one-touch" commands across multiple linked components. When enabled by the manufacturer, CEC allows system-wide behaviors like one-touch play or one-touch record where pressing a single button on the remote launches a series of coordinated commands. HDMI 1.3 provides for Lip Sync capability, whereby synchronization of audio with the corresponding video is completed with very high accuracy. HDMI is well-suited for its application in the living room, but HDMI falls short for broad application to high-performance PC displays due to limitations in terms of scalability and the fact that its primary market focus is on consumer electronics box-tobox connectivity. DisplayPort DisplayPort is a display interface and is governed by VESA (Video Electronics Standards Association). It was primarily designed for use between a PC and its display, leaving HDMI to holds its position with consumer electronics devices and in the living room. DisplayPort was designed to replace VGA and DVI. Since DisplayPort technology is now integrated into all main-stream general-purpose processors (GPU) and integrated GPU chip sets, DisplayPort receptacles are beginning to appear on most new PC s and notebooks. DisplayPort overcomes some of the limitations faced by HDMI by providing an open standard that consolidates internal and external display signaling. It also has enough bandwidth for future performance scalability. With the latest standard DisplayPort 1.2, bandwidth has gone all the way up to 17.28 Gbps. Embedded DisplayPort (edp) is the new standard for internal display panels and replaces LVDS as the panel interface. The battle for the mobile display interface is still on, and DisplayPort is being enabled in hand-held applications with the introduction of the mini DisplayPort interface. Mini DisplayPort (mdp) was introduced by Apple in 2008 and will be competing with USB 3.0 in laptops and small form factor compute devices. Key advantages of DisplayPort include: Performance Higher display bandwidth of up to 17.28Gbps supports higher resolutions up to 4K x 2K at 60 FPS and 24 bpp. Refresh rates of up to 240 FPS for 1080p at 24 bpp are also supported, as well as rich a color depth up to 48 bpp even at 2560 x 1600 at 60 FPS. 5.4 Gbps link rate increases video data bandwidth to 2160Mbytes/sec of stream bandwidth. Supports high frame rates for 3D gaming PC display applications. 1080P 120Hz performance is already supported by existing DisplayPort 1.1a Source devices. This figure could double with DisplayPort 1.2 Source devices. Can be used to increase TV display capabilities for PC gaming applications, especially for 3D applications. Video over USB Page 4 of 7
Multiple Monitors DisplayPort enables daisy chaining of monitors or supports multiple displays (up to 63 separate A/V streams supported). The number of monitors supported depends upon the resolution of the monitors and varies from 10 WXGA (1280x768) monitors to 2 WQXGA (2560x1600) monitors. 63 AV streams are supported by a time division multiplexing mechanism and virtual source to sink connections are established. Auxiliary Functions A fast auxiliary channel of 720Mbps is available with DisplayPort 1.2. This enables bulk data transfers over a single DisplayPort cable. Example applications include USB mass storage transfers, audio, and camera video transfers. Comparison of Display/Video standards Parameter USB 3.0 HDMI 1.4 DisplayPort 1.2 Raw Bandwidth 5 Gbps 10.2 Gbps 21.6Gbps Effective Bandwidth 4 Gbps 8.16 Gbps 17.28Gbps No. of Pins 8 19 20 Core Architecture Packet based 8b/10 decoding with embedded clock Interface is fixed at one dual simplex differential pair Digitized component video sent at display pixel rate (3 data pairs) Separate pixel clock reference Interface is fixed at 4 high speed differential pairs Micro packet data structure 8b/10b decoding with embedded clock 1,2 or 4 differential pairs depending on bandwidth requirements Max Video Resolution Supported 4096 2160p24, 16bit pixel 4096 2160p24, 36bit pixel 4096 x 2160 @60 24 b pixel Connector Types Standard A/B, Micro A/B TypeA,B,C(mini), D(micro),E Standard and mini Charging Capability Yes No No Installed Base of Core Technology (All Speeds and Revs) 6.5B 1B 40M Auxiliary channel Support No Limited (mainly for remote control) Yes Audio Return Channel Yes Yes No Support for 3D Formats Yes Yes Yes Video over USB Page 5 of 7
Hot Plug Detection Yes Yes Yes Daisychaining/ Multiple Monitor Support Support for Ethernet on the same cable Yes Yes Yes No Yes No Permitted Cable Length 3m No length defined in spec instead there are standards for cables. 15m for video transmission Support for DRM Yes included in HDCP 2.0 Yes HDMI included in HDCP 1.1 onwards Yes DP 1.1 is included in HDCP 1.3 Compatibility with other standards Backwards compatible with USB Backward with HDMI compatible Dual mode DisplayPort supports single-link HDMI Royalty None Requires royalty to Silicon Image None except for HDCP While there are several advantages for connectivity standards such as HDMI in the living room and DisplayPort in monitors, USB has inherent benefits that make it attractive to both markets. The key driver for adoption of USB for video is its ubiquity and low cost. USB is available on all PC platforms and almost all mobile platforms (see Figure 4). It has the largest installed base compared to other standards. Using USB to stream video will mean no additional system cost will be incurred from a transport standpoint. Also, USB does not carry any associated royalty costs like other standards. With the introduction of the new Audio Video class which the USB Implementers Forum is currently working on, there should be plenty of reasons to switch to USB as the interface of choice. Also, as notebooks become thinner and sleeker, there will be a need for a single interface that can support as many peripherals including display and video devices all this can be realized with USB. Video over USB Page 6 of 7
Netbook Ethernet 4-Port Hub SS HOST USB3 HUB Figure 4: USB serving as the universal connectivity interface. Cypress Semiconductor 198 Champion Court San Jose, CA 95134-1709 Phone: 408-943-2600 Fax: 408-943-4730 http://www.cypress.com Cypress Semiconductor Corporation, 2007. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. PSoC Designer, Programmable System-on-Chip, and PSoC Express are trademarks and PSoC is a registered trademark of Cypress Semiconductor Corp. All other trademarks or registered trademarks referenced herein are property of the respective corporations. This Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide patent protection (United States and foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of, and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as specified above is prohibited without the express written permission of Cypress. Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein. Cypress does not assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress product in a life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. Use may be limited by and subject to the applicable Cypress software license agreement. Video over USB Page 7 of 7