By James Barkley, Weidong Mao, Comcast Cable
HTTP based Adaptive Bit Rate (ABR) video delivery to IP enabled CPEs via Content Delivery Network (CDN) for both primary and secondary screens (IP Set-Top Box, mobile devices, etc.) is becoming a common feature of service providers. However, the large installed base of QAM STBs will require QAM based linear and Video On Demand (VOD) delivery for the foreseeable future. Traditional approaches to QAM linear delivery include statistical multiplexing and Multiple Program Transport Stream (MPTS) multicasts. A dedicated content library and purposely-built proprietary CDN have been used for QAM VOD delivery. As video migrates to H.264, separate encoding systems are dedicated to produce non-ABR assets (for QAM delivery), sharing little with the production of ABR assets (for IP delivery). Other video features such as advertising insertion, content encryption, data collection and reporting are also enabled through separate silos for IP and QAM delivery. This will not only increase the overall infrastructure cost, but also require separate operational resources.
A converged CDN platform along with common encoding, packaging and content origin are proposed to enable a single common content delivery platform for both IP and QAM video delivery, supporting all use cases, including linear and VOD. The proposed platform uses an MPEG DASH-TS based Common Intermediate Format (CIF) for packaging, ingest/storage, and delivery. It leverages the common ABR video and audio encoding system for H.264 video and various audio codecs. Legacy QAM video encoding is transitioned from MPTS, statistically multiplexing and multicasting to Single Program Transport Stream (SPTS) CIF segments with HTTP delivery through CDN. A CIF Media Presentation Document (MPD) is developed to describe all the codec and bitrate / resolution profiles for the CIF segments. Common encryption on CIF can be used to enable content security at rest in the storage and through the CDN delivery path. Common reporting and data collection schemes can be applied to the infrastructure. A common advertising system can be enabled for both IP and QAM video. At the edge of the network, the CIF MPD and segments can be converted to the appropriate MPEG-2 MPTS format for QAM and player ABR format (HLS, DASH ISO-BMFF, etc.) in conjunction with Digital Rights Management (DRM) for IP.
This converged content delivery infrastructure allows operators to increase the number of IP video clients while still supporting existing QAM STBs. This approach will result in lower overall capital and operational expenses. The approach will also enable seamless incorporation of the latest generation of ABR and codec technologies into the content delivery platform.