- * - encoding: Set by user, can be NULL.
- * - decoding: Set by libavcodec.
+ * Must be allocated with the av_malloc() family of functions, and will be freed in
+ * avcodec_free_context().
+ * - encoding: Set/allocated by user, freed by libavcodec. Can be NULL.
+ * - decoding: Set/allocated/freed by libavcodec.