I’ve rendered MPEGs in Vegas using the “Insert I-frame at markers” option. Why is it that when I inspect these files with an external tool, I-frames are not always occurring at my marker position?
This feature is intended to make chapter marks on a DVD, frame accurate. To be frame accurate, the start of a group of pictures (GOP) must occur at your marker position, so this feature starts GOPs at markers. In display order, the first frame in a GOP may or may not be an I-frame. The number of B-frames before the first I-frame in the GOP varies depending on the type of the previous frames.
When played on a DVD player, the chapter seeks will display the first frame in the GOP which is exactly where your chapter marker was.
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