mov: Evaluate the movie display matrix

This matrix needs to be applied after all others have (currently only
display matrix from trak), but cannot be handled in movie box, since
streams are not allocated yet. So store it in main context, and apply
it when appropriate, that is after parsing the tkhd one.
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/isom.h

@@ -240,6 +240,7 @@ typedef struct MOVContext {
     uint8_t *decryption_key;
     int decryption_key_len;
     int enable_drefs;
+    int32_t movie_display_matrix[3][3]; ///< display matrix from mvhd
 } MOVContext;
 
 int ff_mp4_read_descr_len(AVIOContext *pb);

libavformat/mov.c

@@ -1240,6 +1240,7 @@ static int mov_read_mdhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
 static int mov_read_mvhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
+    int i;
     int64_t creation_time;
     int version = avio_r8(pb); /* version */
     avio_rb24(pb); /* flags */
@@ -1270,7 +1271,12 @@ static int mov_read_mvhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
     avio_skip(pb, 10); /* reserved */
 
-    avio_skip(pb, 36); /* display matrix */
+    /* movie display matrix, store it in main context and use it later on */
+    for (i = 0; i < 3; i++) {
+        c->movie_display_matrix[i][0] = avio_rb32(pb); // 16.16 fixed point
+        c->movie_display_matrix[i][1] = avio_rb32(pb); // 16.16 fixed point
+        c->movie_display_matrix[i][2] = avio_rb32(pb); //  2.30 fixed point
+    }
 
     avio_rb32(pb); /* preview time */
     avio_rb32(pb); /* preview duration */
@@ -3848,12 +3854,22 @@ static int mov_read_meta(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     return 0;
 }
 
+// return 1 when matrix is identity, 0 otherwise
+#define IS_MATRIX_IDENT(matrix)            \
+    ( (matrix)[0][0] == (1 << 16) &&       \
+      (matrix)[1][1] == (1 << 16) &&       \
+      (matrix)[2][2] == (1 << 30) &&       \
+     !(matrix)[0][1] && !(matrix)[0][2] && \
+     !(matrix)[1][0] && !(matrix)[1][2] && \
+     !(matrix)[2][0] && !(matrix)[2][1])
+
 static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
-    int i;
+    int i, j, e;
     int width;
     int height;
     int display_matrix[3][3];
+    int res_display_matrix[3][3] = { { 0 } };
     AVStream *st;
     MOVStreamContext *sc;
     int version;
@@ -3903,15 +3919,20 @@ static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     sc->width = width >> 16;
     sc->height = height >> 16;
 
-    // save the matrix and add rotate metadata when it is not the default
-    // identity
-    if (display_matrix[0][0] != (1 << 16) ||
-        display_matrix[1][1] != (1 << 16) ||
-        display_matrix[2][2] != (1 << 30) ||
-        display_matrix[0][1] || display_matrix[0][2] ||
-        display_matrix[1][0] || display_matrix[1][2] ||
-        display_matrix[2][0] || display_matrix[2][1]) {
-        int i, j;
+    // apply the moov display matrix (after the tkhd one)
+    for (i = 0; i < 3; i++) {
+        const int sh[3] = { 16, 16, 30 };
+        for (j = 0; j < 3; j++) {
+            for (e = 0; e < 3; e++) {
+                res_display_matrix[i][j] +=
+                    ((int64_t) display_matrix[i][e] *
+                     c->movie_display_matrix[e][j]) >> sh[e];
+            }
+        }
+    }
+
+    // save the matrix when it is not the default identity
+    if (!IS_MATRIX_IDENT(res_display_matrix)) {
         double rotate;
 
         av_freep(&sc->display_matrix);
@@ -3921,7 +3942,7 @@ static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 
         for (i = 0; i < 3; i++)
             for (j = 0; j < 3; j++)
-                sc->display_matrix[i * 3 + j] = display_matrix[i][j];
+                sc->display_matrix[i * 3 + j] = res_display_matrix[i][j];
 
         rotate = av_display_rotation_get(sc->display_matrix);
         if (!isnan(rotate)) {
@@ -3940,7 +3961,8 @@ static int mov_read_tkhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         double disp_transform[2];
 
         for (i = 0; i < 2; i++)
-            disp_transform[i] = hypot(display_matrix[i][0], display_matrix[i][1]);
+            disp_transform[i] = hypot(sc->display_matrix[0 + i],
+                                      sc->display_matrix[3 + i]);
 
         if (disp_transform[0] > 0       && disp_transform[1] > 0 &&
             disp_transform[0] < (1<<24) && disp_transform[1] < (1<<24) &&