media: clarify i-frame interval for VPx and HEVC codecs

Bug: 30096321
Change-Id: I421487e6ba3d4054f9a179dc5109a01564b945f4
diff --git a/include/media/openmax/OMX_VideoExt.h b/include/media/openmax/OMX_VideoExt.h
index bf15ee4..92ac109 100644
--- a/include/media/openmax/OMX_VideoExt.h
+++ b/include/media/openmax/OMX_VideoExt.h
@@ -170,7 +170,11 @@
     OMX_U32 nSize;
     OMX_VERSIONTYPE nVersion;
     OMX_U32 nPortIndex;
-    OMX_U32 nKeyFrameInterval;
+    OMX_U32 nKeyFrameInterval;        // distance between consecutive key_frames (including one
+                                      // of the key_frames). 0 means interval is unspecified and
+                                      // can be freely chosen by the codec. 1 means a stream of
+                                      // only key_frames.
+
     OMX_VIDEO_ANDROID_VPXTEMPORALLAYERPATTERNTYPE eTemporalPattern;
     OMX_U32 nTemporalLayerCount;
     OMX_U32 nTemporalLayerBitrateRatio[OMX_VIDEO_ANDROID_MAXVP8TEMPORALLAYERS];
@@ -227,7 +231,10 @@
     OMX_U32 nPortIndex;
     OMX_VIDEO_HEVCPROFILETYPE eProfile;
     OMX_VIDEO_HEVCLEVELTYPE eLevel;
-    OMX_U32 nKeyFrameInterval;
+    OMX_U32 nKeyFrameInterval;        // distance between consecutive I-frames (including one
+                                      // of the I frames). 0 means interval is unspecified and
+                                      // can be freely chosen by the codec. 1 means a stream of
+                                      // only I frames.
 } OMX_VIDEO_PARAM_HEVCTYPE;
 
 /** Structure to define if dependent slice segments should be used */