Add encoder side validation of the cropping window setting

av2/av2_cx_iface.c

@@ -741,6 +741,58 @@ static avm_codec_err_t validate_config(avm_codec_alg_priv_t *ctx,
   RANGE_CHECK_HI(extra_cfg, crop_win_right_offset, 65535);
   RANGE_CHECK_HI(extra_cfg, crop_win_top_offset, 65535);
   RANGE_CHECK_HI(extra_cfg, crop_win_bottom_offset, 65535);
+  if (extra_cfg->enable_cropping_window) {
+    // The decoder validates the conformance window in
+    // av2_validate_seq_conformance_window() and
+    // av2_validate_frame_level_conformance(), rejecting the stream with
+    // AVM_CODEC_UNSUP_BITSTREAM. Apply the same constraints here so an
+    // undecodable configuration is refused rather than producing a bitstream
+    // the reference decoder cannot decode.
+    const int left = extra_cfg->crop_win_left_offset;
+    const int right = extra_cfg->crop_win_right_offset;
+    const int top = extra_cfg->crop_win_top_offset;
+    const int bottom = extra_cfg->crop_win_bottom_offset;
+    const int max_width = cfg->g_forced_max_frame_width
+                              ? (int)cfg->g_forced_max_frame_width
+                              : (int)cfg->g_w;
+    const int max_height = cfg->g_forced_max_frame_height
+                               ? (int)cfg->g_forced_max_frame_height
+                               : (int)cfg->g_h;
+    // Mirrors av2_validate_seq_conformance_window() in the decoder: each offset
+    // must be less than the sequence maximum. The left+right and top+bottom
+    // terms additionally keep conformance requirements 3 and 4 satisfied at
+    // every coded frame size, which the checks below can only cover for g_w and
+    // g_h.
+    if (left >= max_width || right >= max_width || left + right >= max_width) {
+      ERROR(
+          "crop_win_left_offset and crop_win_right_offset must each be less "
+          "than the frame width, and must not together span it");
+    }
+    if (top >= max_height || bottom >= max_height ||
+        top + bottom >= max_height) {
+      ERROR(
+          "crop_win_top_offset and crop_win_bottom_offset must each be less "
+          "than the frame height, and must not together span it");
+    }
+    const int LeftPosX = (left * (int)cfg->g_w) / max_width;
+    const int RightPosX =
+        (int)cfg->g_w - 1 - ((right * (int)cfg->g_w) / max_width);
+    const int TopPosY = (top * (int)cfg->g_h) / max_height;
+    const int BottomPosY =
+        (int)cfg->g_h - 1 - ((bottom * (int)cfg->g_h) / max_height);
+    // Conformance requirement 3: LeftPosX<= RightPosX
+    if (LeftPosX > RightPosX) {
+      ERROR(
+          "crop_win_left_offset and crop_win_right_offset leave no samples in "
+          "the frame");
+    }
+    // Conformance requirement 4: TopPosY <= BottomPosY
+    if (TopPosY > BottomPosY) {
+      ERROR(
+          "crop_win_top_offset and crop_win_bottom_offset leave no samples in "
+          "the frame");
+    }
+  }
 
   RANGE_CHECK_HI(extra_cfg, sharpness, 7);
   RANGE_CHECK_HI(extra_cfg, arnr_max_frames, 15);
@@ -3341,6 +3393,12 @@ static avm_codec_err_t encoder_encode(avm_codec_alg_priv_t *ctx,
         av2_check_initial_width(cpi_lap, subsampling_x, subsampling_y);
       }
 
+      // The coded subsampling is only settled by av2_check_initial_width()
+      // above, so the cropping window's chroma alignment can only be checked
+      // from here on.
+      av2_validate_crop_window_chroma_alignment(cpi, cpi->common.width,
+                                                cpi->common.height);
+
       // Store the original flags in to the frame buffer. Will extract the
       // key frame flag when we actually encode this frame.
       if (av2_receive_raw_frame(cpi, flags | ctx->next_frame_flags, &sd,

av2/encoder/encoder.c

@@ -2501,6 +2501,40 @@ static void init_ref_frame_bufs(AV2_COMP *cpi) {
   }
 }
 
+void av2_validate_crop_window_chroma_alignment(AV2_COMP *cpi, int frame_width,
+                                               int frame_height) {
+  AV2_COMMON *const cm = &cpi->common;
+  const SequenceHeader *const seq_params = &cm->seq_params;
+  const struct CropWindow *const conf = &seq_params->conf;
+  if (!conf->conf_win_enabled_flag) return;
+
+  const int SubX = seq_params->subsampling_x + 1;
+  const int SubY = seq_params->subsampling_y + 1;
+  const int LeftPosX =
+      (conf->conf_win_left_offset * frame_width) / seq_params->max_frame_width;
+  const int TopPosY =
+      (conf->conf_win_top_offset * frame_height) / seq_params->max_frame_height;
+
+  // Conformance requirement 1: LeftPosX == SubX * (LeftPosX/Subx)
+  if (!seq_params->monochrome && SubX > 1 &&
+      LeftPosX != SubX * (LeftPosX / SubX)) {
+    avm_internal_error(&cm->error, AVM_CODEC_INVALID_PARAM,
+                       "crop_win_left_offset puts the conformance window left "
+                       "position %d off the chroma grid at coded width %d: it "
+                       "must be a multiple of SubX=%d",
+                       LeftPosX, frame_width, SubX);
+  }
+  // Conformance requirement 2: TopPosY == SubY * (TopPosY / SubY)
+  if (!seq_params->monochrome && SubY > 1 &&
+      TopPosY != SubY * (TopPosY / SubY)) {
+    avm_internal_error(&cm->error, AVM_CODEC_INVALID_PARAM,
+                       "crop_win_top_offset puts the conformance window top "
+                       "position %d off the chroma grid at coded height %d: it "
+                       "must be a multiple of SubY=%d",
+                       TopPosY, frame_height, SubY);
+  }
+}
+
 void av2_check_initial_width(AV2_COMP *cpi, int subsampling_x,
                              int subsampling_y) {
   AV2_COMMON *const cm = &cpi->common;
@@ -2616,6 +2650,9 @@ void av2_set_frame_size(AV2_COMP *cpi, int width, int height) {
 
     av2_noise_estimate_init(&cpi->noise_estimate, cm->width, cm->height);
   }
+
+  av2_validate_crop_window_chroma_alignment(cpi, cm->width, cm->height);
+
   if (cm->bridge_frame_info.is_bridge_frame) {
     cm->bridge_frame_info.bridge_frame_max_height = cm->height;
     cm->bridge_frame_info.bridge_frame_max_width = cm->width;

av2/encoder/encoder.h

@@ -3123,6 +3123,9 @@ void av2_change_config(AV2_COMP *cpi, const AV2EncoderConfig *oxcf);
 void av2_check_initial_width(AV2_COMP *cpi, int subsampling_x,
                              int subsampling_y);
 
+void av2_validate_crop_window_chroma_alignment(AV2_COMP *cpi, int frame_width,
+                                               int frame_height);
+
 void av2_init_seq_coding_tools(AV2_COMP *cpi, SequenceHeader *seq,
                                AV2_COMMON *cm, const AV2EncoderConfig *oxcf);