Update parseAV2SequenceHeader() for AVM CWG-E103

In https://gitlab.com/AOMediaCodec/avm/-/merge_requests/1183, the syntax
elements for the max frame width and height and color_config() were
moved to the beginning of the sequence header OBU.
parseAV2SequenceHeader() needs to be updated if AVM has this change.
Since this change has not appeared in an AVM release tag, add the
AVIF_ENABLE_CWG_E103 macro to indicate whether AVM has this change.

To facilitate the changes to parseAV2SequenceHeader(), split
parseSequenceHeaderProfile() into two functions:
  - parseSequenceHeaderProfile() parses only seq_profile
  - parseSequenceHeaderLevelIdxAndTier parses seq_level_idx and seq_tier
and change parseSequenceHeaderColorConfig() to not parse
separate_uv_delta_q.

src/obu.c

@@ -141,7 +141,11 @@ static avifBool parseSequenceHeaderProfile(avifBits * bits, avifSequenceHeader *
         return AVIF_FALSE;
     }
     header->av1C.seqProfile = (uint8_t)seq_profile;
+    return !bits->error;
+}
 
+static avifBool parseSequenceHeaderLevelIdxAndTier(avifBits * bits, avifSequenceHeader * header)
+{
     uint32_t still_picture = avifBitsRead(bits, 1);
     header->reduced_still_picture_header = (uint8_t)avifBitsRead(bits, 1);
     if (header->reduced_still_picture_header && !still_picture) {
@@ -255,6 +259,7 @@ static avifBool parseSequenceHeaderEnabledFeatures(avifBits * bits, avifSequence
     return !bits->error;
 }
 
+// Note: Does not parse separate_uv_delta_q.
 static avifBool parseSequenceHeaderColorConfig(avifBits * bits, avifSequenceHeader * header)
 {
     header->bitDepth = 8;
@@ -340,16 +345,13 @@ static avifBool parseSequenceHeaderColorConfig(avifBits * bits, avifSequenceHead
         header->av1C.chromaSubsamplingY = (uint8_t)subsampling_y;
     }
 
-    if (!mono_chrome) {
-        avifBitsRead(bits, 1); // separate_uv_delta_q
-    }
-
     return !bits->error;
 }
 
 static avifBool parseAV1SequenceHeader(avifBits * bits, avifSequenceHeader * header)
 {
     AVIF_CHECK(parseSequenceHeaderProfile(bits, header));
+    AVIF_CHECK(parseSequenceHeaderLevelIdxAndTier(bits, header));
 
     AVIF_CHECK(parseSequenceHeaderFrameMaxDimensions(bits, header));
     avifBitsRead(bits, 1); // use_128x128_superblock
@@ -358,6 +360,9 @@ static avifBool parseAV1SequenceHeader(avifBits * bits, avifSequenceHeader * hea
     avifBitsRead(bits, 3); // enable_superres, enable_cdef, enable_restoration
 
     AVIF_CHECK(parseSequenceHeaderColorConfig(bits, header));
+    if (!header->av1C.monochrome) {
+        avifBitsRead(bits, 1); // separate_uv_delta_q
+    }
 
     avifBitsRead(bits, 1); // film_grain_params_present
     return !bits->error;
@@ -367,8 +372,26 @@ static avifBool parseAV1SequenceHeader(avifBits * bits, avifSequenceHeader * hea
 // See https://gitlab.com/AOMediaCodec/avm/-/blob/main/av1/decoder/decodeframe.c
 static avifBool parseAV2SequenceHeader(avifBits * bits, avifSequenceHeader * header)
 {
+#if defined(AVIF_ENABLE_CWG_E103)
+    // See read_sequence_header_obu() in avm.
+    AVIF_CHECK(parseSequenceHeaderProfile(bits, header));
+
+    uint32_t frame_width_bits = avifBitsRead(bits, 4) + 1;
+    uint32_t frame_height_bits = avifBitsRead(bits, 4) + 1;
+    header->maxWidth = avifBitsRead(bits, frame_width_bits) + 1;   // max_frame_width
+    header->maxHeight = avifBitsRead(bits, frame_height_bits) + 1; // max_frame_height
+
+    // See av1_read_color_config() in avm.
+    AVIF_CHECK(parseSequenceHeaderColorConfig(bits, header));
+
+    // See read_sequence_header_obu() in avm.
+    AVIF_CHECK(parseSequenceHeaderLevelIdxAndTier(bits, header));
+
+    return !bits->error;
+#else  // !defined(AVIF_ENABLE_CWG_E103)
     // See read_sequence_header_obu() in avm.
     AVIF_CHECK(parseSequenceHeaderProfile(bits, header));
+    AVIF_CHECK(parseSequenceHeaderLevelIdxAndTier(bits, header));
 
     // See av1_read_sequence_header() in avm.
     AVIF_CHECK(parseSequenceHeaderFrameMaxDimensions(bits, header));
@@ -388,6 +411,7 @@ static avifBool parseAV2SequenceHeader(avifBits * bits, avifSequenceHeader * hea
     // See av1_read_color_config() in avm.
     AVIF_CHECK(parseSequenceHeaderColorConfig(bits, header));
     // Ignored fields.
+    //   separate_uv_delta_q
     //   base_y_dc_delta_q
     //   base_uv_dc_delta_q
 
@@ -398,6 +422,7 @@ static avifBool parseAV2SequenceHeader(avifBits * bits, avifSequenceHeader * hea
     // See av1_read_sequence_header_beyond_av1() in avm.
     // Other ignored fields.
     return !bits->error;
+#endif // defined(AVIF_ENABLE_CWG_E103)
 }
 #endif