All TC1 recordings produce a companion preview file which helps with quality and playback of the MOV file. If you delete preview files and attempt to add your recordings back into the DDR, you will then receive the 'T' icon indicating the clip needs to be transcoded. Ensure you leave preview files in place to avoid the extra step of having to transcode native recordings again.
For more information on the Transcode feature, please refer to Section 11.2.5 of the TC1 User Guide. http://new.tk/Manual-TC1-01