Having enough digital storage space. Training police officers on a new policy. And funding an initiative that, if implemented department-wide, could cost more than $2 million per year.

Those are some of the challenges the Philadelphia Police Department has encountered while expanding its body camera program, the subject of a City Council committee hearing Monday afternoon.

"We're all literally building a plane as we're flying it," Police Commissioner Richard Ross said.

Mirroring a push in big cities from Oakland, Calif., to Dallas and Baltimore, Philadelphia police in 2014 started using body cameras in North Philadelphia's 22nd District. Ross said all officers up to the rank of lieutenant in that district now wear body cameras during their shifts.

Officers in the 24th and 25th Districts, two of the city's most violent, will be outfitted with cameras by the summer, Ross said. And Mayor Kenney pledged to spend $2.75 million over five years to purchase 4,000 cameras, which Ross said could outfit most patrol officers in the department.

But purchasing the hardware is just the first step, Ross told Council's committee on public safety. Acquiring the software and storage space to handle hours of large video files has proved more difficult and costly, and officials say it would cost more than $2 million per year to roll out and maintain the cameras and footage across every police district.

Others who testified at the hearing raised issues such as how long to store videos where no crime is recorded, and whether to allow officers to see videos before they create written reports of the crime.

Michael Mellon of the Defender Association of Philadelphia told Council members that police with cameras should be pushed to start their recordings earlier.

"Generally, we're not seeing a lot of what led to the initial interaction," he said.

SEPTA Transit Police Chief Thomas Nestel, whose entire force started wearing body cameras last year, said the department did regular audits and reviewed hundreds of incidents to try to increase the rate at which officers turned on their cameras.

Equipping men and women with the technology but not ensuring they use it would be a "huge fail," Nestel said.

Ross said citizen complaints in the 22nd District had gone down since the introduction of the camera program, a correlation he says is the result of having officers wear cameras.

Sgt. Jay Bowen of the digital media evidence unit demonstrated for the committee how a camera works, recording while he spoke and then immediately displaying the video on a projector. Having quick access to videos could prove useful for officers in the aftermath of a crime, he said.

District Attorney Seth Williams said video can also be compelling in court, a surer way to present evidence than relying on witnesses who might not show up or change their testimony.

But Williams, Ross, and Bowen all cautioned that expanding the program could have unforeseen consequences, which is why the department has moved deliberately in introducing cameras.

Councilman Curtis Jones Jr. said, "There's going to be a lot of lawyers that make a lot of money off of this kind of newness."