YouTube exec: Viacom lawsuit would severely harm company; Viacom once tried to buy YouTube

But separately, Viacom-YouTube court documents released Thursday reveal a previously unknown fact: Viacom "repeatedly" tried to buy YouTube, according to Levine.

Court papers show Viacom made the first move before October 2006, when Google purchased YouTube for about $1.6 billion. Consequently, Levine said it made little sense that Viacom once hoped to partner with a video venture it has recently likened to "Napster or Grokster" -- two file-sharing websites federal judges have hammered for copyright infringement.

But Viacom executives have since pointed to a series of e-mails, also released Thursday, that show YouTube executives once looked the other way on most of the company's copyright claims.

However, Levine stressed those e-mails had been taken out of context, adding that Viacom continued uploading videos, even as it began to launch copyright complaints.

Consequently, YouTube promised Thursday to continue fighting the lawsuit aggressively in court.

"We look forward to defending YouTube, and upholding the balance that Congress struck in the DMCA to protect the rights of copyright holders, the progress of technological innovation, and the public interest in free expression," Levine said.