It showed Bancroft seeming to rub the rough side of the ball, the opposite side to which he would usually be trying to shine on his trousers, as is permitted under ICC playing conditions, espncricinfo.com reported.
He appeared to put the object down his pants apparently after being spoken to by the substitute Peter Handscomb, who had come on to the field after speaking to coach Darren Lehmann over the walkie-talkie.
When Bancroft spoke to the umpires, he was shown holding a bigger, black cloth rather than the small yellow object he had earlier seemed to place down his trousers.
Both South African and Australian commentators on the host broadcaster, SuperSport, said Bancroft's actions looked extremely suspicious.
Andy Pycroft, the match referee, charged Bancroft with a Level 2 offence of attempting to alter the condition of the ball.
Former South Africa captain Graeme Smith said he was surprised the umpires had not changed the ball, despite the fact that Bancroft had tampered with the ball.
"In my opinion, I think he's tampered with the ball and used an object to do that. It does look like it's a bit of sandpaper. The footage doesn't look good. I'm quite amazed the umpires haven't done anything with the ball. The footage is quite damning," Graeme said.
"If it is proved that what has gone on in the footage is correct then some tough questions have to be asked of Steve Smith and Darren Lehmann. I think there is a lot of questions that need to be answered and Australia needs to answer them. For me it's quite obvious that he's doing something with the ball and the umpires need to do something about it," he added.
Meanwhile, Smith, who admitted the charges, felt regretted and said, "The leadership group knew about it. We spoke about it at lunch," he said. "I am not proud of what's happened. It's not within the spirit of the game. My integrity, the team's integrity and the leadership group's integrity have come into question. It won't happen again."
Owing to the ball-tampering saga, South Africa were in a strong position with the score reading 238 for 5 after 72 overs.
They currently lead Australia by 294 runs. The Proteas would be hoping to win the Cape Town and go 2-1 up in the four-match Test series.
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