Introduction

The increasing number of different ways that consumers can obtain content presents a challenge to media organizations for distribution. As well as feeding the traditional channels, perhaps via linear infrastructure, a myriad of different versions are required to feed the various direct-to-consumer services. Broadcast centres have simplified their workflows by establishing a common mezzanine or “house format” to which all incoming content is normalized. New workflows that need to support High Dynamic Range (HDR) video and Next Generation Audio (NGA) require a new mezzanine specification. The Repository File workflow, proposed by Dolby Laboratories, takes advantage of advances in standards for HDR, NGA and IP Transport while offering simplicity and flexibility.

 

Simplification is achieved as all downstream processes, such as playout or QC, are required to process a single format. This reduces cost of product implementation as well as improving reliability. Following on from specifications like AS-11 by the DPP and OP1a by SMPTE (ST 378) the Repository File uses the MXF (SMPTE ST 377) file format as the base container. This solution is particularly valuable for broadcasters and multi-service operators managing complex distribution requirements, simplifying distribution from a single asset. While requiring initial investment, the Repository File workflow offers long-term operational benefits and quality improvements across the content distribution chain.

 

What is the Repository File?

The Repository File is a Mezzanine file format, based on MXF supporting HDR video and NGA. It is a single item, single package file conforming to the OP1a operational pattern as defined in SMPTE (ST 378). The file can be played out directly in real-time, typically to a down-stream emission encoder. A key characteristic of the Repository File is the support for dynamic video and audio metadata. The use of dynamic video metadata helps with maintaining a consistent experience across consumer devices with varying capabilities while enabling new features for the consumer. With consumers demanding a more personalized experience, there is a trend towards the separation of audio elements during production. For example, the separation of dialogue audio elements enables features such as multi-language delivery and dialogue enhancement. Insertion of metadata on a frame-by-frame basis simplifies switching and editing scenarios.

 

Such metadata may change dynamically within a given asset or change periodically as assets are played out on a schedule. New metadata standards such as SMPTE ST 2110-41 enable transport of dynamic metadata through a modern media facility. The needs of different media organizations vary considerably requiring flexible solutions that will be widely adopted and achieve reduced cost through scale. To illustrate this flexibility three use-cases are discussed below.

 

Use Case 1: Matched House and Playout Formats

Figure 1. Workflow using matched house and playout formats

 

The objective of this use-case is the reduction of mezzanine files, QC cycles and workflows. A single repository file is used for linear playout and VOD. Typically, linear playout workflows run at a higher frame-rate requiring real-time frame rate conversion during play-out. For example, 25fps may be selected as the frame-rate for the house format with linear play-out occurring at 50fps allowing for easy playback of file-based content.

The benefits of this approach are the reduction in complexity and processing within the content management system. More specifically, for any title there is only one proxy created and one QC cycle for both VOD and Linear.

The main disadvantage is the unnecessary frame-rate conversion of VOD content which could compromise quality. Frame-rates for VOD content tend to vary with 24fps being common for cinematic content and 30fps common for TV. When using a matched house and playout format, VOD assets will all use the single frame rate that has been selected as the house format.

 

Use Case 2: Unmatched House & Playout Formats (Playout Repository File)

Figure 2. Workflow using unmatched house and playout formats

 

The objective of this use-case is to provide the best quality and reliability for both VOD and Linear. There are increased mezzanine files, QC cycles and per title workflows than Use Case 1. While VOD assets are generated directly from the house repository file, for linear playout an intermediate file is used. The Playout Repository File is encoded differently according to the requirements of linear distribution, typically at a higher frame rate. This file is temporary according to the time window of the linear scheduling system. The benefits of this use case are video quality and consistency of experience. Distribution of VOD content in its native frame rate yields a better viewing experience. For Live/Linear services, the conversion of audio, video and associated metadata in the file domain allows for more complex processing than is possible during real-time playout.

 

Use Case 3. Optimized Master Delivery

Today, studios typically deliver mastered content in either IMF (SMPTE ST 2067) packages, ProRes MOV formats or another high- quality file formats. While these approaches work well for delivery of a title to multiple distribution partners, sometimes there is a requirement to deliver a mezzanine for a specific distributor. In such cases, these complex formats require excessive processing that can be avoided. The use of a Repository File enables delivery in a mastered, high-quality format but without the need for a lot of processing.

 

What are the benefits of the Repository File?

The Repository File concept presents a solution for integration of HDR Video and Next Generation Audio into modern broadcast IP facilities while providing options to balance quality and cost. It combines proven and widely adopted technologies like MXF with new standards like SMPTE ST 2110-41 that take full advantage of new IP infrastructure.

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