thumbnailTimestampPct property
Timestamp location of thumbnail image calculated as a percentage value of the video's duration. To convert from a second-wise timestamp to a percentage, divide the desired timestamp by the total duration of the video. If this value is not set, the default thumbnail image will be from 0s of the video.
default value: 0 min value: 0 max value: 1
e.g: 0.529241
Implementation
double thumbnailTimestampPct;