diff --git a/fbchat/_client.py b/fbchat/_client.py
index e977679..62ad30c 100644
--- a/fbchat/_client.py
+++ b/fbchat/_client.py
@@ -1,3 +1,4 @@
+import datetime
 import time
 import json
 import requests
@@ -2109,15 +2110,19 @@ class Client:
         j = self._payload_post("/ajax/mercury/delete_messages.php?dpr=1", data)
         return True
 
-    def muteThread(self, mute_time=-1, thread_id=None):
+    def muteThread(self, mute_time=None, thread_id=None):
         """Mute thread.
 
         Args:
-            mute_time: Mute time in seconds, leave blank to mute forever
+            mute_time (datetime.timedelta): Time to mute, use ``None`` to mute forever
             thread_id: User/Group ID to mute. See :ref:`intro_threads`
         """
         thread_id, thread_type = self._getThread(thread_id, None)
-        data = {"mute_settings": str(mute_time), "thread_fbid": thread_id}
+        if mute_time is None:
+            mute_settings = -1
+        else:
+            mute_settings = _util.timedelta_to_seconds(mute_time)
+        data = {"mute_settings": str(mute_settings), "thread_fbid": thread_id}
         j = self._payload_post("/ajax/mercury/change_mute_thread.php?dpr=1", data)
 
     def unmuteThread(self, thread_id=None):
@@ -2126,7 +2131,7 @@ class Client:
         Args:
             thread_id: User/Group ID to unmute. See :ref:`intro_threads`
         """
-        return self.muteThread(0, thread_id)
+        return self.muteThread(datetime.timedelta(0), thread_id)
 
     def muteThreadReactions(self, mute=True, thread_id=None):
         """Mute thread reactions.
@@ -2468,7 +2473,9 @@ class Client:
         elif delta_type == "rtc_call_log":
             thread_id, thread_type = getThreadIdAndThreadType(metadata)
             call_status = delta["untypedData"]["event"]
-            call_duration = int(delta["untypedData"]["call_duration"])
+            call_duration = _util.seconds_to_timedelta(
+                int(delta["untypedData"]["call_duration"])
+            )
             is_video_call = bool(int(delta["untypedData"]["is_video_call"]))
             if call_status == "call_started":
                 self.onCallStarted(
@@ -3595,7 +3602,7 @@ class Client:
             mid: The action ID
             caller_id: The ID of the person who ended the call
             is_video_call: True if it was video call
-            call_duration: Call duration in seconds
+            call_duration (datetime.timedelta): Call duration
             thread_id: Thread ID that the action was sent to. See :ref:`intro_threads`
             thread_type (ThreadType): Type of thread that the action was sent to. See :ref:`intro_threads`
             ts: A timestamp of the action
diff --git a/fbchat/_file.py b/fbchat/_file.py
index db3ebf1..b475663 100644
--- a/fbchat/_file.py
+++ b/fbchat/_file.py
@@ -1,4 +1,5 @@
 import attr
+from . import _util
 from ._attachment import Attachment
 
 
@@ -36,7 +37,7 @@ class AudioAttachment(Attachment):
     filename = attr.ib(None)
     #: URL of the audio file
     url = attr.ib(None)
-    #: Duration of the audio clip in milliseconds
+    #: Duration of the audio clip as a timedelta
     duration = attr.ib(None)
     #: Audio type
     audio_type = attr.ib(None)
@@ -49,7 +50,7 @@ class AudioAttachment(Attachment):
         return cls(
             filename=data.get("filename"),
             url=data.get("playable_url"),
-            duration=data.get("playable_duration_in_ms"),
+            duration=_util.millis_to_timedelta(data.get("playable_duration_in_ms")),
             audio_type=data.get("audio_type"),
         )
 
@@ -175,7 +176,7 @@ class VideoAttachment(Attachment):
     width = attr.ib(None)
     #: Height of original video
     height = attr.ib(None)
-    #: Length of video in milliseconds
+    #: Length of video as a timedelta
     duration = attr.ib(None)
     #: URL to very compressed preview video
     preview_url = attr.ib(None)
@@ -243,7 +244,7 @@ class VideoAttachment(Attachment):
         return cls(
             width=data.get("original_dimensions", {}).get("width"),
             height=data.get("original_dimensions", {}).get("height"),
-            duration=data.get("playable_duration_in_ms"),
+            duration=_util.millis_to_timedelta(data.get("playable_duration_in_ms")),
             preview_url=data.get("playable_url"),
             small_image=data.get("chat_image"),
             medium_image=data.get("inbox_image"),
@@ -255,7 +256,7 @@ class VideoAttachment(Attachment):
     def _from_subattachment(cls, data):
         media = data["media"]
         return cls(
-            duration=media.get("playable_duration_in_ms"),
+            duration=_util.millis_to_timedelta(media.get("playable_duration_in_ms")),
             preview_url=media.get("playable_url"),
             medium_image=media.get("image"),
             uid=data["target"].get("video_id"),
diff --git a/fbchat/_util.py b/fbchat/_util.py
index 09ad6f1..61dec26 100644
--- a/fbchat/_util.py
+++ b/fbchat/_util.py
@@ -269,3 +269,21 @@ def datetime_to_millis(dt):
     The returned milliseconds will be rounded to the nearest whole number.
     """
     return round(dt.timestamp() * 1000)
+
+
+def seconds_to_timedelta(seconds):
+    """Convert seconds to a timedelta."""
+    return datetime.timedelta(seconds=seconds)
+
+
+def millis_to_timedelta(milliseconds):
+    """Convert a duration (in milliseconds) to a timedelta object."""
+    return datetime.timedelta(milliseconds=milliseconds)
+
+
+def timedelta_to_seconds(td):
+    """Convert a timedelta to seconds.
+
+    The returned seconds will be rounded to the nearest whole number.
+    """
+    return round(td.total_seconds())