視頻編碼中，經常提到I幀。I幀只使用幀內壓縮，不能除去幀間冗余度。P幀做幀間編碼，根據當前幀與前面最近的I幀或P幀的差別來編碼。
另外一個比較少提到的概念是IDR幀。IDR屬於I幀，但是I幀不一定是IDR幀。只有IDR幀，才有SPS和PPS。解碼器收到IDR幀時，將reference buffer清空；而收到I幀不會清空reference buffer。也就是說，對某個IDR幀之后的幀，解碼器不會參考這個IDR幀之前的任何幀做解碼。對某個I幀之后的幀，解碼器可能會參考這個I幀之前的幀做解碼。還可以參考文檔https://malleshamdasari.wordpress.com/2013/07/31/difference-between-i-frame-and-idr-frame/。
在Xilinx VCU GStreamer里，使用參數periodicity-idr指定IDR幀的間隔。在Xilinx VCU Ctrl-SW里，使用參數Gop.FreqIDR指定IDR幀的間隔。PG252里的說明如下：
IDR picture frequency
periodicity-idr
Specifies the number of frames between consecutive
instantaneous decoder refresh (IDR) pictures. The periodicity-
idr property was formerly called gop-freq-idr.
Allowed values: <Positive value> or -1 to disable IDR insertion
Default value: 0 (first frame is IDR)
Gop.FreqIDR Specifies the minimum number of frames between two IDR pictures (AVC and HEVC). IDR
insertion depends on the position of the GOP boundary.
Allowed values: positive integer or -1 to disable IDR region.
Default value: -1