mp4: Document the purpose of each atom.

This gives the reader a rough idea about the atoms we care about.

diff --git a/mp4.c b/mp4.c
index b6bab088d60da392ff98cc98a77b6dafcc291b0c..4b8607b185a9a87c845940d86412843654a13c7d 100644 (file)
--- a/mp4.c
+++ b/mp4.c
@@ -133,25 +133,25 @@ static int read_int16(struct mp4 *f, uint16_t *result)
 
 /** A macro defining the atoms we care about. It gets expanded twice. */
 #define ATOM_ITEMS \
-       ATOM_ITEM(MOOV, 'm', 'o', 'o', 'v') \
-       ATOM_ITEM(TRAK, 't', 'r', 'a', 'k') \
-       ATOM_ITEM(MDIA, 'm', 'd', 'i', 'a') \
-       ATOM_ITEM(MINF, 'm', 'i', 'n', 'f') \
-       ATOM_ITEM(STBL, 's', 't', 'b', 'l') \
-       ATOM_ITEM(UDTA, 'u', 'd', 't', 'a') \
+       ATOM_ITEM(MOOV, 'm', 'o', 'o', 'v') /* movie (top-level container) */ \
+       ATOM_ITEM(TRAK, 't', 'r', 'a', 'k') /* container for a single track */ \
+       ATOM_ITEM(MDIA, 'm', 'd', 'i', 'a') /* media information */ \
+       ATOM_ITEM(MINF, 'm', 'i', 'n', 'f') /* extends mdia */ \
+       ATOM_ITEM(STBL, 's', 't', 'b', 'l') /* sample table container */ \
+       ATOM_ITEM(UDTA, 'u', 'd', 't', 'a') /* user data */ \
        ATOM_ITEM(ILST, 'i', 'l', 's', 't') /* iTunes Metadata list */ \
-       ATOM_ITEM(ARTIST, 0xa9, 'A', 'R', 'T') \
-       ATOM_ITEM(TITLE, 0xa9, 'n', 'a', 'm') \
-       ATOM_ITEM(ALBUM, 0xa9, 'a', 'l', 'b') \
-       ATOM_ITEM(DATE, 0xa9, 'd', 'a', 'y') \
-       ATOM_ITEM(COMMENT, 0xa9, 'c', 'm', 't') \
+       ATOM_ITEM(ARTIST, 0xa9, 'A', 'R', 'T') /* artist */ \
+       ATOM_ITEM(TITLE, 0xa9, 'n', 'a', 'm') /* title */ \
+       ATOM_ITEM(ALBUM, 0xa9, 'a', 'l', 'b') /* album */ \
+       ATOM_ITEM(DATE, 0xa9, 'd', 'a', 'y') /* date */ \
+       ATOM_ITEM(COMMENT, 0xa9, 'c', 'm', 't') /* comment */ \
        ATOM_ITEM(MDHD, 'm', 'd', 'h', 'd') /* track header */ \
        ATOM_ITEM(STSD, 's', 't', 's', 'd') /* sample description box */ \
        ATOM_ITEM(STTS, 's', 't', 't', 's') /* time to sample box */ \
        ATOM_ITEM(STSZ, 's', 't', 's', 'z') /* sample size box */ \
        ATOM_ITEM(STCO, 's', 't', 'c', 'o') /* chunk offset box */ \
        ATOM_ITEM(STSC, 's', 't', 's', 'c') /* sample to chunk box */ \
-       ATOM_ITEM(MP4A, 'm', 'p', '4', 'a') \
+       ATOM_ITEM(MP4A, 'm', 'p', '4', 'a') /* mp4 audio */ \
        ATOM_ITEM(META, 'm', 'e', 't', 'a') /* iTunes Metadata box */ \
        ATOM_ITEM(DATA, 'd', 'a', 't', 'a') /* iTunes Metadata data box */ \