From 772b2d585bc8334f59a751b8aefcfef5e30478ea Mon Sep 17 00:00:00 2001
From: Patrick Gansterer <paroga@paroga.com>
Date: Sun, 30 Apr 2023 16:30:05 +0200
Subject: [PATCH] Fix parsing of senc box

---
 src/pymp4/parser.py | 10 ++++++----
 tests/test_box.py   | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/src/pymp4/parser.py b/src/pymp4/parser.py
index e3ab8b2..a78c542 100644
--- a/src/pymp4/parser.py
+++ b/src/pymp4/parser.py
@@ -725,14 +725,16 @@ def _encode(self, obj, context):
         "has_subsample_encryption_info" / Flag,
         Padding(1)
     ),
-    "sample_encryption_info" / PrefixedArray(Int32ub, Struct(
+    "sample_encryption_info" / IfThenElse(this.flags.has_subsample_encryption_info, PrefixedArray(Int32ub, Struct(
         "iv" / Bytes(8),
         # include the sub sample encryption information
-        "subsample_encryption_info" / Default(If(this.flags.has_subsample_encryption_info, PrefixedArray(Int16ub, Struct(
+        "subsample_encryption_info" / PrefixedArray(Int16ub, Struct(
             "clear_bytes" / Int16ub,
             "cipher_bytes" / Int32ub
-        ))), None)
-    ))
+        )),
+    )), PrefixedArray(Int32ub, Struct(
+        "iv" / Bytes(8),
+    ))),
 )
 
 OriginalFormatBox = Struct(
diff --git a/tests/test_box.py b/tests/test_box.py
index 44937ed..696e664 100644
--- a/tests/test_box.py
+++ b/tests/test_box.py
@@ -104,6 +104,29 @@ def test_moov_build(self):
             b'\x00\x00\x00\x20trex\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
         )
 
+    def test_senc_parse(self):
+        in_bytes = b'\x00\x00\x00\x18senc\x00\x00\x00\x00\x00\x00\x00\x01abcdefgh'
+        self.assertEqual(
+            Box.parse(in_bytes + b'padding'),
+            Container(offset=0)
+            (type=b"senc")(version=0)(flags=Container(has_subsample_encryption_info=False))
+            (sample_encryption_info=[
+                Container(iv=b'abcdefgh')
+            ])(end=len(in_bytes))
+        )
+
+        in_bytes = b'\x00\x00\x00\x20senc\x00\x00\x00\x02\x00\x00\x00\x01abcdefgh\x00\x01\x99\x88\x77\x66\x55\x44'
+        self.assertEqual(
+            Box.parse(in_bytes + b'padding'),
+            Container(offset=0)
+            (type=b"senc")(version=0)(flags=Container(has_subsample_encryption_info=True))
+            (sample_encryption_info=[
+                Container(iv=b'abcdefgh', subsample_encryption_info=[
+                    Container(clear_bytes=0x9988, cipher_bytes=0x77665544)
+                ])
+            ])(end=len(in_bytes))
+        )
+
     def test_smhd_parse(self):
         in_bytes = b'\x00\x00\x00\x10smhd\x00\x00\x00\x00\x00\x00\x00\x00'
         self.assertEqual(