Add cropping metadata

06.bitstream.syntax.md

@@ -427,6 +427,8 @@ at least one byte of the payload data (including the trailing bit) shall not be
 |         metadata_scalability( )
 |     else if ( metadata_type == METADATA_TYPE_TIMECODE )
 |         metadata_timecode( )
+|     else if ( metadata_type == METADATA_TYPE_CROP )
+|         metadata_crop( )
 | }
 {:.syntax }
 
@@ -572,6 +574,23 @@ at least one byte of the payload data (including the trailing bit) shall not be
 | }
 {:.syntax }
 
+#### Metadata cropping syntax
+
+| --------------------------------------------------------- | ---------------- |
+| metadata_crop( ) {                                        | **Type**
+|     @@crop_width_minus_1                                  | f(16)
+|     @@crop_height_minus_1                                 | f(16)
+|     @@crop_offset_present                                 | f(1)
+|     if ( crop_offset_present == 1 ) {
+|         @@crop_x_offset                                   | f(16)
+|         @@crop_y_offset                                   | f(16)
+|     } else {
+|         crop_x_offset = 0
+|         crop_y_offset = 0
+|     }
+| }
+{:.syntax }
+
 ### Frame header OBU syntax
 
 #### General frame header OBU syntax

07.bitstream.semantics.md

@@ -575,7 +575,8 @@ Metadata OBUs may or may not have an OBU extension header. If there is no extens
 | 4              | METADATA_TYPE_ITUT_T35      | payload-specific
 | 5              | METADATA_TYPE_TIMECODE      | N
 | 6-31           | Unregistered user private   | -
-| 32 and greater | Reserved for AOM use        | -
+| 32             | METADATA_TYPE_CROP          | Y
+| 33 and greater | Reserved for AOM use        | -
 {:.table .table-sm .table-bordered }
 
 The semantics of the column “Layer-specific” and its values are defined in Section 6.2.2. 
@@ -1314,6 +1315,41 @@ coded video sequence.
 number of bits used to represent time_offset_value is equal to time_offset_length. When
 time_offset_value is not present, its value is inferred to be equal to 0.
 
+#### Metadata crop semantics
+
+When present the metadata_crop OBU applies starting at the next frame in the sequence 
+with matching temporal_id and spatial_id, and shall apply to all matching frames until the next Key Frame
+or metadata_crop OBU. The output picture should be cropped to the region as specified in the 
+cropping metadata OBU. When applied, the crop shall be after all normal decode operations as a 
+post-processing step (after film grain synthesis in the output process).  This metadata has no 
+effect on the decoding process.
+
+**crop_x_offset** specifies the minimum pixel column containing picture data which should be rendered.
+
+**crop_y_offset** specifies the minimum pixel row containing picture data which should be rendered.
+
+**crop_width_minus_1** specifies the number of pixel columns minus 1 which which should be rendered after applying crop_x_offset.
+
+**crop_height_minus_1** specifies the number of pixel rows minus 1 which which should be rendered after applying crop_y_offset.
+
+If RenderWidth or RenderHeight are present in the frame header, then render width and height 
+shall be applied after cropping. 
+
+The total cropped area shall not exceed the frame size:
+
+ * crop_width_minus_1 + crop_x_offset shall be less than or equal to frame_width_minus_1.
+ * crop_height_minus_1 + crop_y_offset shall be less than or equal to frame_height_minus_1.
+
+The crop area shall align with the chroma subsampling grid:
+
+ * crop_x_offset and crop_width_minus_1 + 1 must both be a multiple of subsampling_x + 1.
+ * crop_y_offset and crop_height_minus_1 + 1 must both be a multiple of subsampling_y + 1.
+
+When muxed into a container that supports signaling cropping information, this metadata should 
+be removed from the bitstream and included in the container’s signaling mechanism.  
+If both the container and bitstream signal cropping information, then the container’s cropping 
+information takes precedence.
+
 ### Frame header OBU semantics
 
 #### General frame header OBU semantics