diff --git a/src/avb/bin.py b/src/avb/bin.py
index 3050c91..f4876cb 100644
--- a/src/avb/bin.py
+++ b/src/avb/bin.py
@@ -232,6 +232,7 @@ def __init__(self):
             self.sifted_settings.append(s)
 
         self.attributes = self.root.create.Attributes()
+        self.mob_dict ={}
 
     def read(self, f):
         super(Bin, self).read(f)
@@ -255,6 +256,7 @@ def read(self, f):
             object_count = ctx.read_u32(f)
 
         self.items = []
+        self.mob_dict ={}
 
         for i in range(object_count):
             bin_obj = BinItem.__new__(BinItem, root=self.root)
diff --git a/src/avb/components.py b/src/avb/components.py
index 6f614cc..7ede820 100644
--- a/src/avb/components.py
+++ b/src/avb/components.py
@@ -313,6 +313,9 @@ def write(self, f):
 
     @property
     def mob(self):
+        if not self.root.content.mob_dict:
+            self.root.content.build_mob_dict()
+
         if hasattr(self, 'mob_id'):
             mob_id = self.mob_id
             if mob_id:
diff --git a/src/avb/trackgroups.py b/src/avb/trackgroups.py
index f029f7d..c951afb 100644
--- a/src/avb/trackgroups.py
+++ b/src/avb/trackgroups.py
@@ -7,11 +7,11 @@
 import datetime
 
 from . import core
-from .core import AVBPropertyDef, AVBRefList
-from .components import Component
+from .core import AVBPropertyDef, walk_references
 from . import utils
 from . import mobid
 from . utils import peek_data
+from .components import Component, SourceClip
 
 TRACK_LABEL_FLAG            = 1 << 0
 TRACK_ATTRIBUTES_FLAG       = 1 << 1
@@ -225,6 +225,37 @@ def write(self, f):
                 else:
                     ctx.write_s16(f, 0)
 
+    def dependant_mobs(self):
+        """
+            Yields all mobs that this mob is dependant on in depth first order.
+        """
+
+        visited = set()
+        stack = [self]
+
+        if not self.root.content.mob_dict:
+            self.root.content.build_mob_dict()
+
+        while stack:
+            mob = stack[-1]
+            children_processed = True
+
+            for obj in walk_references(mob):
+                if isinstance(obj, SourceClip):
+                    ref_mob = obj.mob
+                    if not ref_mob:
+                        continue
+                    if ref_mob.mob_id not in visited:
+                        stack.append(ref_mob)
+                        children_processed = False
+
+            if children_processed:
+                stack.pop(-1)
+                if mob.mob_id not in visited:
+                    visited.add(mob.mob_id)
+                    if mob is not self:
+                        yield mob
+
 
 @utils.register_class
 class TrackEffect(TrackGroup):
diff --git a/tests/test_copy.py b/tests/test_copy.py
index 8df63bc..455f3cf 100644
--- a/tests/test_copy.py
+++ b/tests/test_copy.py
@@ -37,5 +37,64 @@ def test_copy(self):
                     assert mob_b
                     compare(mob_a, mob_b)
 
+    def test_copy_mastermob_depends(self):
+        result_file = os.path.join(result_dir, 'copy_mastermobs.avb')
+
+        mob_ids = set()
+        with avb.open(test_file_01) as a:
+            with avb.open() as b:
+                mobs = {}
+                for mob in a.content.mastermobs():
+                    mobs[mob.mob_id] = mob
+                    for m in mob.dependant_mobs():
+                        mobs[m.mob_id] = m
+
+                for mob in mobs.values():
+                    mob_ids.add(mob.mob_id)
+                    new_mob = mob.copy(b)
+                    b.content.add_mob(new_mob)
+
+
+                b.write(result_file)
+
+        with avb.open(test_file_01) as a:
+            with avb.open(result_file) as b:
+                b.content.build_mob_dict()
+                a.content.build_mob_dict()
+                for mob_id in mob_ids:
+                    mob_a = a.content.mob_dict.get(mob_id, None)
+                    mob_b = b.content.mob_dict.get(mob_id, None)
+                    compare(mob_a, mob_b)
+
+    def test_copy_compositionmobs(self):
+        result_file = os.path.join(result_dir, 'copy_compositionmob.avb')
+
+        mob_ids = set()
+        with avb.open(test_file_01) as a:
+            with avb.open() as b:
+
+                mobs = {}
+                for mob in a.content.compositionmobs():
+                    mobs[mob.mob_id] = mob
+                    for m in mob.dependant_mobs():
+                        mobs[m.mob_id] = m
+
+                for mob in mobs.values():
+                    mob_ids.add(mob.mob_id)
+                    new_mob = mob.copy(b)
+                    b.content.add_mob(new_mob)
+
+
+                b.write(result_file)
+
+        with avb.open(test_file_01) as a:
+            with avb.open(result_file) as b:
+                b.content.build_mob_dict()
+                a.content.build_mob_dict()
+                for mob_id in mob_ids:
+                    mob_a = a.content.mob_dict.get(mob_id, None)
+                    mob_b = b.content.mob_dict.get(mob_id, None)
+                    compare(mob_a, mob_b)
+
 if __name__ == "__main__":
     unittest.main()