diff --git a/doc/mkdwarfs.md b/doc/mkdwarfs.md
index 5e6378bc..4fd595e6 100644
--- a/doc/mkdwarfs.md
+++ b/doc/mkdwarfs.md
@@ -383,6 +383,22 @@ Most other options are concerned with compression tuning:
   Don't add a creation timestamp. This is useful when bit-identical file
   system images are required to be produced from the same input.
 
+- `--no-category-names`:
+  Don't add category names to the file system. This is only relevant if
+  the file system uses categories at all. Adding category names allows
+  for setting per-category options when rewriting a file system, to get
+  per-category info with `dwarfsck`, or to see the categories that have
+  been identified in a file. This implicitly adds `--no-category-metadata`.
+
+- `--no-category-metadata`:
+  Don't add category metadata to the file system. This goes beyond just
+  the category names and additionally stores the metadata identified
+  during categorization. This metadata is needed for metadata-dependent
+  compression algorithms (e.g. FLAC). So if you're planning to recompress
+  categorized blocks from a metadata-independent to a metadata-dependent
+  compression algorithm, this is going to be impossible if the metadata
+  information is not available.
+
 - `--file-hash=none`|*name*:
   Select the hashing function to be used for file deduplication. If `none`
   is chosen, file deduplication is disabled. By default, the built-in
diff --git a/include/dwarfs/writer/internal/block_manager.h b/include/dwarfs/writer/internal/block_manager.h
index 126bff38..f24c4735 100644
--- a/include/dwarfs/writer/internal/block_manager.h
+++ b/include/dwarfs/writer/internal/block_manager.h
@@ -38,16 +38,14 @@ class block_manager {
 
   size_t get_logical_block() const;
   void set_written_block(size_t logical_block, size_t written_block,
-                         fragment_category::value_type category);
+                         fragment_category category);
   void map_logical_blocks(std::vector<chunk_type>& vec) const;
-  std::vector<fragment_category::value_type>
-  get_written_block_categories() const;
+  std::vector<fragment_category> get_written_block_categories() const;
 
  private:
   std::mutex mutable mx_;
   size_t mutable num_blocks_{0};
-  std::vector<std::optional<std::pair<size_t, fragment_category::value_type>>>
-      block_map_;
+  std::vector<std::optional<std::pair<size_t, fragment_category>>> block_map_;
 };
 
 } // namespace dwarfs::writer::internal
diff --git a/include/dwarfs/writer/internal/metadata_builder.h b/include/dwarfs/writer/internal/metadata_builder.h
index b0292839..09d089a8 100644
--- a/include/dwarfs/writer/internal/metadata_builder.h
+++ b/include/dwarfs/writer/internal/metadata_builder.h
@@ -87,6 +87,15 @@ class metadata_builder {
     impl_->set_block_categories(std::move(block_categories));
   }
 
+  void set_category_metadata_json(std::vector<std::string> metadata_json) {
+    impl_->set_category_metadata_json(std::move(metadata_json));
+  }
+
+  void
+  set_block_category_metadata(std::map<uint32_t, uint32_t> block_metadata) {
+    impl_->set_block_category_metadata(std::move(block_metadata));
+  }
+
   void add_symlink_table_entry(size_t index, uint32_t entry) {
     impl_->add_symlink_table_entry(index, entry);
   }
@@ -121,6 +130,10 @@ class metadata_builder {
     set_category_names(std::vector<std::string> category_names) = 0;
     virtual void
     set_block_categories(std::vector<uint32_t> block_categories) = 0;
+    virtual void
+    set_category_metadata_json(std::vector<std::string> metadata_json) = 0;
+    virtual void set_block_category_metadata(
+        std::map<uint32_t, uint32_t> block_metadata) = 0;
     virtual void add_symlink_table_entry(size_t index, uint32_t entry) = 0;
     virtual void gather_chunks(inode_manager const& im, block_manager const& bm,
                                size_t chunk_count) = 0;
diff --git a/include/dwarfs/writer/metadata_options.h b/include/dwarfs/writer/metadata_options.h
index 837419dc..090149d6 100644
--- a/include/dwarfs/writer/metadata_options.h
+++ b/include/dwarfs/writer/metadata_options.h
@@ -53,6 +53,8 @@ struct metadata_options {
   bool pack_symlinks_index{false};
   bool force_pack_string_tables{false};
   bool no_create_timestamp{false};
+  bool no_category_names{false};
+  bool no_category_metadata{false};
   size_t inode_size_cache_min_chunk_count{128};
 };
 
diff --git a/src/reader/internal/metadata_v2.cpp b/src/reader/internal/metadata_v2.cpp
index 88ec5426..6835f195 100644
--- a/src/reader/internal/metadata_v2.cpp
+++ b/src/reader/internal/metadata_v2.cpp
@@ -294,6 +294,8 @@ void analyze_frozen(std::ostream& os,
     }                                                                          \
   } while (0)
 
+#define META_OPT_MAP_SIZE(x) META_OPT_LIST_SIZE(x)
+
 #define META_OPT_STRING_LIST_SIZE(x)                                           \
   do {                                                                         \
     if (auto list = meta.x()) {                                                \
@@ -402,6 +404,8 @@ void analyze_frozen(std::ostream& os,
 
   META_OPT_STRING_LIST_SIZE(category_names);
   META_OPT_LIST_SIZE(block_categories);
+  META_OPT_STRING_LIST_SIZE(category_metadata_json);
+  META_OPT_MAP_SIZE(block_category_metadata);
 
 #undef META_LIST_SIZE
 #undef META_OPT_STRING_SET_SIZE
diff --git a/src/writer/internal/block_manager.cpp b/src/writer/internal/block_manager.cpp
index 8737d5a3..272ebd2c 100644
--- a/src/writer/internal/block_manager.cpp
+++ b/src/writer/internal/block_manager.cpp
@@ -38,7 +38,7 @@ size_t block_manager::get_logical_block() const {
 
 void block_manager::set_written_block(size_t logical_block,
                                       size_t written_block,
-                                      fragment_category::value_type category) {
+                                      fragment_category category) {
   std::lock_guard lock{mx_};
   assert(logical_block < num_blocks_);
   if (block_map_.size() < num_blocks_) {
@@ -56,9 +56,9 @@ void block_manager::map_logical_blocks(std::vector<chunk_type>& vec) const {
   }
 }
 
-std::vector<fragment_category::value_type>
+std::vector<fragment_category>
 block_manager::get_written_block_categories() const {
-  std::vector<fragment_category::value_type> result;
+  std::vector<fragment_category> result;
 
   {
     std::lock_guard lock{mx_};
diff --git a/src/writer/internal/metadata_builder.cpp b/src/writer/internal/metadata_builder.cpp
index 733547dc..ed796234 100644
--- a/src/writer/internal/metadata_builder.cpp
+++ b/src/writer/internal/metadata_builder.cpp
@@ -95,6 +95,16 @@ class metadata_builder_ final : public metadata_builder::impl {
     md_.block_categories() = std::move(block_categories);
   }
 
+  void
+  set_category_metadata_json(std::vector<std::string> metadata_json) override {
+    md_.category_metadata_json() = std::move(metadata_json);
+  }
+
+  void set_block_category_metadata(
+      std::map<uint32_t, uint32_t> block_metadata) override {
+    md_.block_category_metadata() = std::move(block_metadata);
+  }
+
   void add_symlink_table_entry(size_t index, uint32_t entry) override {
     DWARFS_NOTHROW(md_.symlink_table()->at(index)) = entry;
   }
@@ -314,6 +324,17 @@ thrift::metadata::metadata const& metadata_builder_<LoggerPolicy>::build() {
     ti << "saving symlinks table...";
   }
 
+  if (options_.no_category_names) {
+    md_.category_names().reset();
+    md_.block_categories().reset();
+  }
+
+  if (options_.no_category_names || options_.no_category_metadata) {
+    md_.category_metadata_json().reset();
+    md_.block_category_metadata().reset();
+  }
+
+  // TODO: don't overwrite all options when upgrading!
   md_.options() = fsopts;
   md_.features() = features_.get();
   md_.dwarfs_version() = std::string("libdwarfs ") + DWARFS_GIT_ID;
diff --git a/src/writer/scanner.cpp b/src/writer/scanner.cpp
index 0a58e5ae..b863f891 100644
--- a/src/writer/scanner.cpp
+++ b/src/writer/scanner.cpp
@@ -43,6 +43,8 @@
 
 #include <fmt/format.h>
 
+#include <range/v3/view/enumerate.hpp>
+
 #include <dwarfs/error.h>
 #include <dwarfs/file_access.h>
 #include <dwarfs/history.h>
@@ -826,8 +828,7 @@ void scanner_<LoggerPolicy>::scan(
                   [blockmgr, logical_block_num,
                    category](auto physical_block_num) {
                     blockmgr->set_written_block(logical_block_num,
-                                                physical_block_num,
-                                                category.value());
+                                                physical_block_num, category);
                   },
                   meta);
             });
@@ -918,30 +919,51 @@ void scanner_<LoggerPolicy>::scan(
   mdb.set_shared_files_table(std::move(ssfv.get_shared_files()));
 
   if (auto catmgr = options_.inode.categorizer_mgr) {
-    std::unordered_map<fragment_category::value_type,
-                       fragment_category::value_type>
+    std::unordered_map<fragment_category::value_type, uint32_t>
         category_indices;
+    std::unordered_map<fragment_category, uint32_t> category_metadata_indices;
     std::vector<std::string> category_names;
+    std::vector<std::string> category_metadata;
 
     category_indices.reserve(frag_info.info.size());
     category_names.reserve(frag_info.info.size());
 
     for (auto const& ci : frag_info.info) {
-      auto [it, inserted] =
-          category_indices.emplace(ci.category, category_names.size());
-      if (inserted) {
+      if (category_indices.emplace(ci.category, category_names.size()).second) {
         category_names.emplace_back(catmgr->category_name(ci.category));
       }
     }
 
+    for (auto const& cat : frag_info.categories) {
+      auto metadata = catmgr->category_metadata(cat);
+      if (!metadata.empty()) {
+        if (category_metadata_indices.emplace(cat, category_metadata.size())
+                .second) {
+          category_metadata.emplace_back(std::move(metadata));
+        }
+      }
+    }
+
     auto written_categories = blockmgr->get_written_block_categories();
+    std::vector<uint32_t> block_categories(written_categories.size());
+    std::map<uint32_t, uint32_t> block_cat_metadata;
 
     std::transform(written_categories.begin(), written_categories.end(),
-                   written_categories.begin(),
-                   [&](auto const& cat) { return category_indices.at(cat); });
+                   block_categories.begin(), [&](auto const& cat) {
+                     return category_indices.at(cat.value());
+                   });
+
+    for (auto const& [i, cat] : ranges::views::enumerate(written_categories)) {
+      if (auto it = category_metadata_indices.find(cat);
+          it != category_metadata_indices.end()) {
+        block_cat_metadata.emplace(i, it->second);
+      }
+    }
 
     mdb.set_category_names(std::move(category_names));
-    mdb.set_block_categories(std::move(written_categories));
+    mdb.set_block_categories(std::move(block_categories));
+    mdb.set_category_metadata_json(std::move(category_metadata));
+    mdb.set_block_category_metadata(std::move(block_cat_metadata));
   }
 
   mdb.set_block_size(segmenter_factory_.get_block_size());
diff --git a/test/segmenter_benchmark.cpp b/test/segmenter_benchmark.cpp
index 7c55627d..89162f45 100644
--- a/test/segmenter_benchmark.cpp
+++ b/test/segmenter_benchmark.cpp
@@ -154,7 +154,7 @@ void run_segmenter_benchmark(::benchmark::State& state, unsigned granularity,
                            auto logical_block_num) {
           auto physical_block_num = written.size();
           written.push_back(blk);
-          blkmgr->set_written_block(logical_block_num, physical_block_num, 0);
+          blkmgr->set_written_block(logical_block_num, physical_block_num, {});
         });
 
     // begin benchmarking code
diff --git a/thrift/metadata.thrift b/thrift/metadata.thrift
index a504eb50..e03e40a4 100644
--- a/thrift/metadata.thrift
+++ b/thrift/metadata.thrift
@@ -422,4 +422,18 @@ struct metadata {
 
   // Size cache for highly fragmented file inodes
   30: optional inode_size_cache reg_file_size_cache
+
+  //==========================================================//
+  // fields added with dwarfs-0.13.0, file system version 2.5 //
+  //==========================================================//
+
+  // Unique block categorization metadata JSON strings. These
+  // can be used to compress a block with a metadata-dependent
+  // algorithm after having been compressed with a general
+  // purpose algorithm.
+  31: optional list<string>     category_metadata_json
+
+  // The metadata associated with each block. Maps from block
+  // number to index into `categorization_metadata_json`.
+  32: optional map<UInt32, UInt32> block_category_metadata
 }
diff --git a/tools/src/mkdwarfs_main.cpp b/tools/src/mkdwarfs_main.cpp
index f64f1fbc..863e893b 100644
--- a/tools/src/mkdwarfs_main.cpp
+++ b/tools/src/mkdwarfs_main.cpp
@@ -663,6 +663,12 @@ int mkdwarfs_main(int argc, sys_char** argv, iolayer const& iol) {
     ("time-resolution",
         po::value<std::string>(&time_resolution)->default_value("sec"),
         resolution_desc.c_str())
+    ("no-category-names",
+        po::value<bool>(&options.metadata.no_category_names)->zero_tokens(),
+        "don't add category names to file system")
+    ("no-category-metadata",
+        po::value<bool>(&options.metadata.no_category_metadata)->zero_tokens(),
+        "don't add category metadata to file system")
     ("pack-metadata,P",
         po::value<std::string>(&pack_metadata)->default_value("auto"),
         "pack certain metadata elements (auto, all, none, chunk_table, "