diff --git a/pipeline/utils.py b/pipeline/utils.py
index 7775cbc..9c8555a 100644
--- a/pipeline/utils.py
+++ b/pipeline/utils.py
@@ -14,3 +14,97 @@ class SourceMedia():
     }]
 
     It should be possible to combine/merge/aggregate multiple SourceMedia into one
+    TODO: consider if we actually want that or if we just loop over a list of >0 SourceMedia
+
+    Iterating over a SourceMedia object should return a list of Source objects.
+    """
+
+    def __init__(self, sources=[]):
+        self.sources = sources
+
+    def __iter__(self):
+        return iter(self.sources)
+
+class Source():
+    """A Source is a single media file (eg), used to populate SourceMedia objects.
+
+    JSON type schema:
+    {
+        "source": "/path/to/video.mp4",
+        "path": "/path/to/video.mp4",
+        "provider": "FileInputJSON"
+    }
+    def __init__(self, source, path, provider):
+        if not source:
+            raise ValueError("Source must be provided") # TODO: #API -- decide if this is necessary
+        self.source = source
+        if not path:
+        # we need a file to work on for the rest of the pipeline
+            raise ValueError("Path must be provided")
+        self.path = path
+        if not provider:
+            raise ValueError("Provider must be provided") # TODO: #API -- decide if this is necessary
+        self.provider = provider
+    def __str__(self):
+        """See: 'accessing the object should return the path to the media file'"""
+        return self.path
+
+    def __repr__(self):
+        return f"Source({self.source}, {self.path}, {self.provider})"
+class Interval():
+    """An interval of time in a media file
+
+    This can be defined by a start and end time, a start time and a duration, or an end time and a duration.
+
+    Instance variables:
+
+    start -- the start time of the interval
+    end -- the end time of the interval
+    duration -- the duration of the interval (end - start)
+
+    Notes:
+
+    Sorts by start time, then end time
+    """
+    # TODO: decide if ABC or will be used directly
+    # TODO: have default duration for intervals set by config
+    # TODO: consider if we want to permit adjusting intervals (eg, start time, end time, duration) [probably yes]
+    # NOTE: if we have more ways of defining, we could consider multipledispatch?
+
+    DEFAULT_DURATION = 5 # seconds
+    DEFAUT_PRECISION = 3 # decimal places
+    def __init__(self, start=None, end=None, duration=None):
+        if start is None and end is None and duration is None:
+            raise ValueError("Two of start, end, or duration must be provided")
+        if start is not None and end is not None and duration is not None:
+            raise ValueError("Only two of start, end, or duration may be provided")
+
+        # start and end
+        if start is not None and end is not None:
+            # some trivial validation
+            if start > end:
+                raise ValueError("Start time must be before end time")
+            self.start = start
+            self.end = end
+            self.duration = end - start
+
+        # start and duration
+        elif start is not None and duration is not None:
+            if duration < 0:
+                raise ValueError("Duration must be positive")
+            self.start = start
+            self.duration = duration
+            self.end = start + duration
+
+        # end and duration
+        elif end is not None and duration is not None:
+            if duration < 0:
+                raise ValueError("Duration must be positive")
+            self.end = end
+            self.duration = duration
+            self.start = end - duration
+    @classmethod
+    def from_start(cls, start=None):
+        """Create an interval from a start time using the default duration"""
+        return cls(start=start, duration=cls.DEFAULT_DURATION)
+