diff --git a/src/fuchsia/write/trace_fuchsia_write.ml b/src/fuchsia/write/trace_fuchsia_write.ml
index 65a69a0..4bed4cb 100644
--- a/src/fuchsia/write/trace_fuchsia_write.ml
+++ b/src/fuchsia/write/trace_fuchsia_write.ml
@@ -90,10 +90,10 @@ module Thread_ref = struct
       invalid_arg "fuchsia: thread inline ref must be >0 < 256";
     Ref x
 
-  let size_B (self : t) : int =
+  let size_word (self : t) : int =
     match self with
     | Ref _ -> 0
-    | Inline _ -> 16
+    | Inline _ -> 2
 
   (** 8-bit int for the reference *)
   let as_i8 (self : t) : int =
@@ -107,10 +107,39 @@ module Metadata = struct
   (** First record in the trace *)
   module Magic_record = struct
     let value = 0x0016547846040010L
-    let size_B = 8
+    let size_word = 1
     let encode (buf : Buf.t) = Buf.add_i64 buf value
   end
 
+  module Initialization_record = struct
+    let size_word = 2
+
+    (** Default: 1 tick = 1 ns *)
+    let default_ticks_per_sec = 1_000_000_000L
+
+    let encode (buf : Buf.t) ~ticks_per_secs () : unit =
+      let hd = I64.(1L lor (of_int size_word lsl 4)) in
+      Buf.add_i64 buf hd;
+      Buf.add_i64 buf ticks_per_secs
+  end
+
+  module Provider_info = struct
+    let size_word ~name () = 1 + (round_to_word (String.length name) lsr 3)
+
+    let encode buf ~(id : int) ~name () : unit =
+      let size = size_word ~name () in
+      let hd =
+        I64.(
+          (of_int size lsl 4)
+          lor (1L lsl 16)
+          lor (of_int id lsl 20)
+          lor (of_int (Str_ref.inline (String.length name)) lsl 52))
+      in
+      Buf.add_i64 buf hd;
+      Buf.add_string buf name
+  end
+
+  module Provider_section = struct end
   module Trace_info = struct end
 end
 
@@ -122,16 +151,17 @@ module Argument = struct
 
   let[@inline] is_i32_ (i : int) : bool = Int32.(to_int (of_int i) = i)
 
-  (** Size in bytes *)
-  let size_B (self : t) =
+  let size_word (self : t) =
     let name, data = self in
     match data with
-    | `None | `Bool _ -> 8 + round_to_word (String.length name)
-    | `Int i when is_i32_ i -> 8 + round_to_word (String.length name)
-    | `Int _ -> (* int64 *) 16 + round_to_word (String.length name)
-    | `Float _ -> 16 + round_to_word (String.length name)
+    | `None | `Bool _ -> 1 + (round_to_word (String.length name) lsr 3)
+    | `Int i when is_i32_ i -> 1 + (round_to_word (String.length name) lsr 3)
+    | `Int _ -> (* int64 *) 2 + (round_to_word (String.length name) lsr 3)
+    | `Float _ -> 2 + (round_to_word (String.length name) lsr 3)
     | `String s ->
-      8 + round_to_word (String.length s) + round_to_word (String.length name)
+      1
+      + (round_to_word (String.length s) lsr 3)
+      + (round_to_word (String.length name) lsr 3)
 
   open struct
     external int_of_bool : bool -> int = "%identity"
@@ -139,7 +169,7 @@ module Argument = struct
 
   let encode (buf : Buf.t) (self : t) : unit =
     let name, data = self in
-    let size = size_B self in
+    let size = size_word self in
 
     (* part of header with argument name + size *)
     let hd_arg_size =
@@ -193,8 +223,8 @@ module Arguments = struct
     List.iter Argument.check_valid self;
     ()
 
-  let[@inline] size_B (self : t) =
-    List.fold_left (fun n arg -> n + Argument.size_B arg) 0 self
+  let[@inline] size_word (self : t) =
+    List.fold_left (fun n arg -> n + Argument.size_word arg) 0 self
 
   let encode (buf : Buf.t) (self : t) =
     let rec aux buf l =
@@ -209,11 +239,13 @@ end
 
 (** record type = 3 *)
 module Thread_record = struct
-  let size_B : int = 24
+  let size_word : int = 3
 
   (** Record that [Thread_ref.ref as_ref] represents the pair [pid, tid] *)
   let encode (buf : Buf.t) ~as_ref ~pid ~tid () : unit =
-    let hd = I64.(3L lor (of_int size_B lsl 4) lor (of_int as_ref lsl 16)) in
+    if as_ref <= 0 || as_ref > 255 then
+      invalid_arg "fuchsia: thread_record: invalid ref";
+    let hd = I64.(3L lor (of_int size_word lsl 4) lor (of_int as_ref lsl 16)) in
     Buf.add_i64 buf hd;
     Buf.add_i64 buf (I64.of_int pid);
     Buf.add_i64 buf (I64.of_int tid)
@@ -222,19 +254,14 @@ end
 (** record type = 4 *)
 module Event = struct
   module Instant = struct
-    (* TODO: find out how to encode tid/pid (are they both in64?)
-
-       then compute size; then add encoder
-    *)
-
-    let size_B ~name ~t_ref ~args () : int =
-      8 + Thread_ref.size_B t_ref + 8
-      (* timestamp *) + round_to_word (String.length name)
-      + Arguments.size_B args
+    let size_word ~name ~t_ref ~args () : int =
+      1 + Thread_ref.size_word t_ref + 1
+      (* timestamp *) + (round_to_word (String.length name) / 8)
+      + Arguments.size_word args
 
     let encode (buf : Buf.t) ~name ~(t_ref : Thread_ref.t) ~time_ns ~args () :
         unit =
-      let size = size_B ~name ~t_ref ~args () in
+      let size = size_word ~name ~t_ref ~args () in
       (* set category = 0 *)
       let hd =
         I64.(
@@ -257,4 +284,38 @@ module Event = struct
       Arguments.encode buf args;
       ()
   end
+
+  module Duration_complete = struct
+    let size_word ~name ~t_ref ~args () : int =
+      1 + Thread_ref.size_word t_ref + 1
+      (* timestamp *) + (round_to_word (String.length name) lsr 3)
+      + Arguments.size_word args + 1 (* end timestamp *)
+
+    let encode (buf : Buf.t) ~name ~(t_ref : Thread_ref.t) ~time_ns ~end_time_ns
+        ~args () : unit =
+      let size = size_word ~name ~t_ref ~args () in
+      (* set category = 0 *)
+      let hd =
+        I64.(
+          4L
+          lor (of_int size lsl 4)
+          lor (4L lsl 16)
+          lor (of_int (List.length args) lsl 20)
+          lor (of_int (Thread_ref.as_i8 t_ref) lsl 24)
+          lor (of_int (Str_ref.inline (String.length name)) lsl 48))
+      in
+      Buf.add_i64 buf hd;
+      Buf.add_i64 buf time_ns;
+
+      (match t_ref with
+      | Thread_ref.Inline { pid; tid } ->
+        Buf.add_i64 buf (I64.of_int pid);
+        Buf.add_i64 buf (I64.of_int tid)
+      | Thread_ref.Ref _ -> ());
+
+      Buf.add_string buf name;
+      Arguments.encode buf args;
+      Buf.add_i64 buf end_time_ns;
+      ()
+  end
 end