It took just four months and £2 million to build a 'good enough' working solution, Clark told attendees at Ignite summit.
Consultants originally quoted ITV £15-30 million to build the solution, it is understood.
Until recently, the broadcaster shot footage on tapes which were digitised for editing, converted back onto tapes post-editing, and then driven around the country for subtitling, audio description and distribution.
Clark explained: "Tapes cost roughly £35 to £40 and when you make 3,500 hours of content every year that gets very expensive. Not only that but it's a very inefficient process and means edits have to be locked in earlier, with scheduling often driven by how fast someone could drive down the M6."
The company wanted to move to shooting, editing and transferring files digitally.
Regarding the initial nine-month external consultation, Clark said: "We paid them loads of money, they spent a long time looking at the problem, interviewed tons of people and wrote stacks of documents and beautiful presentations. They then quoted us a huge figure - we realised basically that they didn't know how much it would cost."
ITV decided to try an agile route for the project with 11 internal IT staff. The team comprised five developers, two testers, two DevOps [developer and operations roles combined], a product manager and a project manager.
As part of its efforts to eliminate the use of tapes, the broadcaster installed its own fibre optic network, connecting its data centres in Slough and Greenwich.
This helped provide sufficient storage and computing power to handle the transcoding and digital distribution of the files, offering the ability to scale from 10 gigbit to terabit capacity if needed.
"The first piece of content to go through the new system was a piece of children's content called Horrid Henry. We got it through the entire chain after four months", Clark said.
He added: "In four months we built a solution consultants took nine months just thinking about. And it was seven to twelve times cheaper than the original quotes."
"The BBC's Digital Media Initiative tried to do file-based delivery. It's not fair to say we did what the BBC did though, it was just a small section of what they tried", Clark said.
Clark gave advice to delegates on implementing agile projects. He emphasised validating assumptions, having small teams and focusing on essential business requirements.
He said: "The first thing that was different about our approach was a sense of humility - you should challenge and validate your assumptions at the beginning. You will make some assumptions that may or may not turn out to be accurate. Check those before you do anything else and keep your teams small. A decent-sized team can be fed on two pizzas."
He added: "If you can't hit the target, cut the scope. If you only ever design what the business absolutely needs then there's no waste: it's lean."
Clark emphasised the importance of transparency when implementing agile projects, and added that it helps ensure executive sponsorship of your project.
"Transparency is critical," he said. Report back regularly with both successes and failures, which generates trust. Agile is not a panacea. Things will go wrong. But if you have transparency your stakeholders can see what you're doing, and they will be supportive.
"Agile doesn't respond well to questions of what is it when will I get it and how much does it cost. Instead it gives you variables; people are used to nice board packs with release plans going over a number of years. That's fine and sometimes it works but often it isn't based on any hard data, so in reality it's a best guess."
He added: "Just ask for some money for a few months, then come back and show them what you've done. The only way to build trust is delivery and transparency."