The #GstVideoTimeCodeInterval to add to tc. The interval must contain valid values, except that for drop-frame timecode, it may also contain timecodes which would normally be dropped. These are then corrected to the next reasonable timecode.
A new #GstVideoTimeCode with tc_inter added or null if the interval can't be added.
This makes a component-wise addition of tc_inter to tc. For example, adding ("01:02:03:04", "00:01:00:00") will return "01:03:03:04". When it comes to drop-frame timecodes, adding ("00:00:00;00", "00:01:00:00") will return "00:01:00;02" because of drop-frame oddities. However, adding ("00:09:00;02", "00:01:00:00") will return "00:10:00;00" because this time we can have an exact minute.