C4 Media Access Project
By Kevin Burrows, CTO, Channel 4 & Spencer Rodd, Technical Director, Pharos. First published in The Channel January 2008 Issue
Save or print this Pharos News Story as a pdf
UK Channel 4 Television has completed the first phase of its media access project, progressing C4 from video tape to an MXF file-based operation. Kevin Burrows,C4's CTO and Spencer Rodd, Technical Director at Pharos, explain about one of the most innovative technical progressions in C4's 25 years.
In 2003 Channel 4 replaced its VHS-based preview facility with a Pharos browse system giving access directly from standard desktop office PCs. The objective was to deliver browse-quality content to relevant staff as efficiently as possible with minimal operational overheads. This would bring the further benefit of eliminating the risk of lost or damaged video tapes. The result was a highly co-ordinated solution centred on a Pharos Mediator media management database. Initially rolled out to 20 desktops and expanded later to 400, this proved very successful and is one of the largest broadcast browse systems in Europe. The media access project was a logical extension of the browse concept, effectively adding in a single architecture all the facilities Channel 4 needed for file-based ingest, long-term storage and playout. Essentially a large library of file-based digital content and metadata, it allowed the channel to create and maintain a tapeless store of all programmes which could then be made available in any format, whether linear TV, video on demand, mobile or whatever might be called for in the future.
Pharos Mediator at Channel 4
The entire media access project - ingest server, content store, archive manager, Petasite tape library and file transfer management - are managed by the Pharos Mediator media management system and database. Pharos Mediator is a scalable broadcast media management system which can be configured to co-ordinate single or multiple workflows in any broadcast environment. Ingested content can be catalogued, researched, loaned and shared between users, providing collaborative working. Files can be outgest to any selected format, such as complete programmes music compilations for post-production or DVDs for local distribution. Multiple client libraries can be configured to provide security and privacy for clients without the expense and complexity of separate hardware for every client.
File Format
An initial challenge was the selection of a generic file format. MXF 50i was chosen on the basis that it maintains optimal quality and is a relatively easy standard to export. If the need arises to send content elsewhere, recipients will be able to use the programme content and the accompanying metadata. Many broadcasters have gone down the road of proprietary IMX. Channel 4 wanted to avoid IMX so that file-users could simply unwrap metadata stored with each file rather than needing to rely on a database. MXF 50i also makes decoding much easier as no additional software is required.
Ingest
Incoming programmes and interstitials are ingested at full 50 Mbit/s I-frame MPEG2 via Omneon ingest servers to an Isilon central online storage system before being automatically transcoded to 15 Mbit/s Long GOP MPEG2 for playout via the existing Pinnacle TX server system. Using Mediator, Channel 4 is able to perform the entire broadcast operation from its online digital library store. The ingest area is equipped with quality control booths for content that needs careful eyeballing and fast-track desks for material that does not need to be viewed in real time. Both are controlled via Mediator. All ingested content is exported to the browse system through MPEG1 encoders at the same time as it is transferred for transmission. The browse system is used for off-air logs, for all compliance viewing and for checking of commercial break running order. A playlist function is already built in. A generic Application Program Interface is used to ensure flexible control.
Online & Archive Storage
Five nodes of Isilon disc storage, totalling 40 terabytes, are accessible for online storage. Everything so far as possible incorporates redundancy, including main and backup Mediator databases, main and backup servers. Ingest is split across two servers so only half of each is lost if a server goes wrong. A 12-drive Sony Petasite LTO3000 based data tape archive provides sufficient capacity for up to 18 months of MXF 50i programmes. Multiple transcoders and multiple data movers interface between the servers and the Petasite. Each LTO3000 takes LTO3 data tape cassettes with a capacity of 400 gigabytes per cassette. Each server controls four Petasite drives. If one server goes down, the eight other drives would continue working. DigiBeta tapes are still held as backups with the option of making local or external copies.
Mediator Outgest.
Mediator manages outgest of video, files and metadata to any chosen destination using an XML interface for metadata. Outgest 1 is DigiBeta, Outgest 2 is Digital Rapids Version X, and so on. Outgest to graphics is handled similarly, exporting clips directly into a Pixel Power Clarity for making promotional graphics. Quite a lot of material is issued on DVD for the Channel 4 press office. This is transcoded from 50i and a logo superimposed. A Pharos database within Mediator makes a title slate which is added to the DVD chapters. Transcoders are used to generate 15 long-GOP files for transmission from Pinnacle servers. All broadcast schedules for a week or more go into the Mediator and that actually drives the transcode process.
Transitional Timescales
The project was anticipated to take 15 months from start to finish. It began about the time when affordable storage costs combined with a growing need to get the media out to the right places. It would have been too expensive a year earlier. Channel 4 wanted a system big enough to handle at least a year's programmes. The Petasite has sufficient capacity to store 12 to 18 months of content. Channel 4 launched its 4oD video-on-demand service a year ago, supplying Tiscali, BT Vision, Virgin Media and the PC download service. The video-on-demand requirement came shortly after installation commenced and meant rescheduling some priorities. Half the system was allocated to deliver the 4oD service and the rest of the system is essentially complete. Time could have been saved by opting for IMX rather than MXF. Starting today, one would certainly go down the MXF route as it is finally becoming fully supported by equipment suppliers. There was no rigid deadline to meet and it was important not to end up with several years of content that would need rewrapping in the future. It was planned that each MXF file should be standalone and potentially readable very far into the future. The Media Access Project greatly simplifies media ingest and outgest. Pharos did a detailed study of workflow within each relevant department of Channel 4. Mediator enabled a starting workflow pattern to be defined for each operator. The ability to reconfigure workflow was also very important. The system has certainly met expectations, streamlining day-to-day workflows and increasing overall efficiency. It has also made engineering planning for additional services much easier. The system itself is very scalable, allowing more storage to be added whenever required.
The Future
For Channel 4's recently launched HD simulcast service on the Sky platform, the first phase has parallel HD ingest to a separate Omneon server which takes HD and SD for short-term storage and playout. HD content is stored on its original master tapes and only compressed for actual transmission. Direct ingest of data files is clearly the future. An increasing number of commercials already arrive at Channel 4 from a server at the end of a line. For programmes, standards and delivery costs are the issues. With three or four Hollyoaks per week, for example, it is far cheaper to put tapes on a bike and send them down from Liverpool rather than wire them as files. The move to HD makes wired delivery of archive-quality programmes even more challenging but that is
obviously the future.
phpr-186
Save or print this Pharos News Story as a pdf
Pharos Mediator Spot Check workflow and user interface for fast content checking prior to QC
Published on 3 Jan 2008