video-converter: reduce minimum lines per CPU core

For multi CPU core video conversion there's a explicitly magic minimum
number of lines to convert per core, set at 200 by upstream. This is
really a tunable that depends on CPU horsepower and use case.

On our systems resolutions converted on CPU is generally low, typically
200 - 300 lines high. That means that CPU conversion only runs on 1 - 2
cores even if usage of all cores were requested. Reduce minimum lines
per core to 50 so that all cores are utilized converting a 200 lines
high frame on a quad core system.

Change-Id: I56894c64271437c637c5541e489f779ecc654559
1 file changed