Document a few more structure change rules with relation to ABI/API.

Originally committed as revision 11283 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -745,6 +745,12 @@ typedef struct AVPanScan{
 
 /**
  * Audio Video Frame.
+ * New fields can be added to the end of FF_COMMON_FRAME with minor version
+ * bumps.
+ * Removial, reordering and changes to existing fields require a Major
+ * version bump. No fields should be added into AVFrame before or after
+ * FF_COMMON_FRAME!
+ * sizeof(AVFrame) must not be used outside libav*
  */
 typedef struct AVFrame {
     FF_COMMON_FRAME

libavformat/avformat.h

@@ -269,6 +269,13 @@ typedef struct AVIndexEntry {
     int min_distance;         /**< min distance between this and the previous keyframe, used to avoid unneeded searching */
 } AVIndexEntry;
 
+/**
+ * Stream structure.
+ * New fields can be added to the end with minor version bumps.
+ * Removial, reordering and changes to existing fields require a Major
+ * version bump.
+ * sizeof(AVStream) must not be used outside libav*
+ */
 typedef struct AVStream {
     int index;    /**< stream index in AVFormatContext */
     int id;       /**< format specific stream id */
@@ -343,6 +350,13 @@ typedef struct AVStream {
 
 #define AV_PROGRAM_RUNNING 1
 
+/**
+ *
+ * New fields can be added to the end with minor version bumps.
+ * Removial, reordering and changes to existing fields require a Major
+ * version bump.
+ * sizeof(AVProgram) must not be used outside libav*
+ */
 typedef struct AVProgram {
     int            id;
     char           *provider_name; ///< Network name for DVB streams