diff --git a/gst/isomp4/atoms.c b/gst/isomp4/atoms.c
index eb32bf78b8..1ea6485317 100644
--- a/gst/isomp4/atoms.c
+++ b/gst/isomp4/atoms.c
@@ -4030,6 +4030,29 @@ build_colr_extension (const GstVideoColorimetry * colorimetry, gboolean is_mp4)
       atom_data_free);
 }
 
+AtomInfo *
+build_clap_extension (gint width_n, gint width_d, gint height_n, gint height_d,
+    gint h_off_n, gint h_off_d, gint v_off_n, gint v_off_d)
+{
+  AtomData *atom_data = atom_data_new (FOURCC_clap);
+  guint8 *data;
+
+  atom_data_alloc_mem (atom_data, 32);
+  data = atom_data->data;
+
+  GST_WRITE_UINT32_BE (data, width_n);
+  GST_WRITE_UINT32_BE (data + 4, width_d);
+  GST_WRITE_UINT32_BE (data + 8, height_n);
+  GST_WRITE_UINT32_BE (data + 12, height_d);
+  GST_WRITE_UINT32_BE (data + 16, h_off_n);
+  GST_WRITE_UINT32_BE (data + 20, h_off_d);
+  GST_WRITE_UINT32_BE (data + 24, v_off_n);
+  GST_WRITE_UINT32_BE (data + 28, v_off_d);
+
+  return build_atom_info_wrapper ((Atom *) atom_data, atom_data_copy_data,
+      atom_data_free);
+}
+
 SampleTableEntryMP4V *
 atom_trak_set_video_type (AtomTRAK * trak, AtomsContext * context,
     VisualSampleEntry * entry, guint32 scale, GList * ext_atoms_list)
diff --git a/gst/isomp4/atoms.h b/gst/isomp4/atoms.h
index f164ebf00a..b56311688e 100644
--- a/gst/isomp4/atoms.h
+++ b/gst/isomp4/atoms.h
@@ -1045,6 +1045,7 @@ AtomInfo *   build_jp2h_extension        (gint width, gint height, const gchar *
 AtomInfo *   build_jp2x_extension        (const GstBuffer * prefix);
 AtomInfo *   build_fiel_extension        (GstVideoInterlaceMode mode, GstVideoFieldOrder order);
 AtomInfo *   build_colr_extension        (const GstVideoColorimetry *colorimetry, gboolean is_mp4);
+AtomInfo *   build_clap_extension        (gint width_n, gint width_d, gint height_n, gint height_d, gint h_off_n, gint h_off_d, gint v_off_n, gint v_off_d);
 AtomInfo *   build_ac3_extension         (guint8 fscod, guint8 bsid,
                                           guint8 bsmod, guint8 acmod,
                                           guint8 lfe_on, guint8 bitrate_code);
diff --git a/gst/isomp4/fourcc.h b/gst/isomp4/fourcc.h
index 076a5f22fa..160e6ca280 100644
--- a/gst/isomp4/fourcc.h
+++ b/gst/isomp4/fourcc.h
@@ -174,6 +174,9 @@ G_BEGIN_DECLS
 #define FOURCC_opus     GST_MAKE_FOURCC('O','p','u','s')
 #define FOURCC_dops     GST_MAKE_FOURCC('d','O','p','s')
 #define FOURCC_pasp     GST_MAKE_FOURCC('p','a','s','p')
+#define FOURCC_colr     GST_MAKE_FOURCC('c','o','l','r')
+#define FOURCC_clap     GST_MAKE_FOURCC('c','l','a','p')
+#define FOURCC_fiel     GST_MAKE_FOURCC('f','i','e','l')
 #define FOURCC_pcst     GST_MAKE_FOURCC('p','c','s','t')
 #define FOURCC_pgap     GST_MAKE_FOURCC('p','g','a','p')
 #define FOURCC_pnot     GST_MAKE_FOURCC('p','n','o','t')
@@ -286,8 +289,6 @@ G_BEGIN_DECLS
 /* ISO Motion JPEG 2000 fourcc */
 #define FOURCC_cdef     GST_MAKE_FOURCC('c','d','e','f')
 #define FOURCC_cmap     GST_MAKE_FOURCC('c','m','a','p')
-#define FOURCC_colr     GST_MAKE_FOURCC('c','o','l','r')
-#define FOURCC_fiel     GST_MAKE_FOURCC('f','i','e','l')
 #define FOURCC_ihdr     GST_MAKE_FOURCC('i','h','d','r')
 #define FOURCC_jp2h     GST_MAKE_FOURCC('j','p','2','h')
 #define FOURCC_jp2x     GST_MAKE_FOURCC('j','p','2','x')
diff --git a/gst/isomp4/gstqtmux.c b/gst/isomp4/gstqtmux.c
index 4a4187d14a..49d59618d8 100644
--- a/gst/isomp4/gstqtmux.c
+++ b/gst/isomp4/gstqtmux.c
@@ -4317,6 +4317,22 @@ gst_qt_mux_video_sink_set_caps (GstQTPad * qtpad, GstCaps * caps)
     mp4v->spatial_quality = 0x3FF;
     mp4v->temporal_quality = 0;
     mp4v->vendor = FOURCC_appl;
+
+    /* The 'clap' extension is also defined for MP4 but inventing values in
+     * general seems a bit tricky for this one. We only write it for ProRes
+     * then, where it is a requirement.
+     *
+     * NTSC and PAL have special values, otherwise just take width and height
+     */
+    if (width == 720 && (height == 480 || height == 486))
+      ext_atom = build_clap_extension (704, 1, height, 1, 0, 1, 0, 1);
+    else if (width == 720 && height == 576)
+      ext_atom = build_clap_extension (768 * 54, 59, 576, 1, 0, 1, 0, 1);
+    else
+      ext_atom = build_clap_extension (width, 1, height, 1, 0, 1, 0, 1);
+
+    if (ext_atom)
+      mp4v->extension_atoms = g_list_append (mp4v->extension_atoms, ext_atom);
   }
 
   gst_object_unref (qtmux);
diff --git a/gst/isomp4/qtdemux_types.c b/gst/isomp4/qtdemux_types.c
index 0208e8b652..693ad5d1cc 100644
--- a/gst/isomp4/qtdemux_types.c
+++ b/gst/isomp4/qtdemux_types.c
@@ -84,6 +84,7 @@ static const QtNodeType qt_node_types[] = {
   {FOURCC_mhdr, "mhdr", QT_FLAG_CONTAINER,},
   {FOURCC_jp2h, "jp2h", QT_FLAG_CONTAINER,},
   {FOURCC_colr, "colr", 0,},
+  {FOURCC_clap, "clap", 0,},
   {FOURCC_ihdr, "ihdr", 0,},
   {FOURCC_fiel, "fiel", 0,},
   {FOURCC_jp2x, "jp2x", 0,},