diff --git a/mudlet_replay_format.txt b/mudlet_replay_format.txt
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+# parsing mudlet replay
+
+* uses big endian signed integers
+* format is: delta, number of bytes, chunk of bytes
+
+## delta
+* may be int32_t or int64_t but probably int32
+* max delta with int32_t is around 12 days
+* try as int32_t first and if num_butes < 1 or delta < 0 or num_bytes > buffer_size where 
+  buffer_size is around 100000L then give up and try with int64_t and run tests again but
+  also add test delta <= int32_max
+* delta change to int64_t was probably in 4.11.0 https://github.com/Mudlet/Mudlet/pull/4400
+* delta fix back to int32_t was probably in 4.15.0 https://github.com/Mudlet/Mudlet/pull/5776
+
+## num_bytes
+* num bytes is int32_t
+
+## chunk of bytes
+* chunk can be assumed utf8, anything mudlet takes will be compatible, but mud probably uses ascii
+
+
+
+