diff --git a/bin/swh-loader-tar-producer b/bin/swh-loader-tar-producer
index d2da48c..d351729 100755
--- a/bin/swh-loader-tar-producer
+++ b/bin/swh-loader-tar-producer
@@ -1,99 +1,135 @@
 #!/usr/bin/env python3
 
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import sys
 import os
 
 from swh.core import config
 from swh.loader.dir import producer
 
 
+# Static setup
+EPOCH = 0
+UTC_OFFSET = '+0000'
+
+
 conf_file = sys.argv[1]
 if not os.path.exists(conf_file):
     conf_file = '../resources/producer/tar.ini'
 
 
 conf = config.read(conf_file)
 
 
 def compute_origin(config, filename):
     return {
         'origin_url': os.path.join(config['origin_url_scheme'], filename),
         'origin_type': config['origin_type'],
     }
 
 
-def compute_release_number(filename):
-    """Compute the release number from a given filename.
-
-    """
-    pass
-
-
 def compute_occurrence(filepath):
     pass
 
 
 def compute_occurrences(filepath):
     pass
 
 
+def time_from_file(filepath):
+    """Extract time from filepath.
+
+    Args:
+        filepath: path to the file we want to extract metadata
+
+    Returns:
+        Modification time from filepath.
+
+    """
+    return os.lstat(filepath).st_mtime
+
+
 def compute_release(filepath):
     """Compute a release from a given filepath.
     If the filepath does not contain a recognizable release number, the release
     can be skipped.
+
+    Args:
+        filepath: file's absolute path
+
+    Returns:
+        None if the release number cannot be extracted from the filename.
+        Otherwise a synthetic release is computed with the following keys:
+            - name: the release computed from the filename
+            - date: the modification timestamp as returned by a fstat call
+            - offset: +0000
+            - author_name: ''
+            - author_email: ''
+            - comment: ''
+
     """
-    pass
+    filename = os.path.basename(filepath)
+    release_number = producer.release_number(filename)
+    if release_number:
+        return {
+            'name': release_number,
+            'date': time_from_file(filepath),
+            'offset': UTC_OFFSET,
+            'author_name': '',
+            'author_email': '',
+            'comment': '',
+        }
+    return None
 
 
 def compute_revision(filepath):
     pass
 
 
 def compute_from_filepath(filepath):
     pass
 
 
 def list_archives_from(path):
     """From path, produce archive tarball message to celery.
 
     Args:
         path: top directory to list archives from.
 
     """
     for dirpath, dirnames, filenames in os.walk(path):
         for fname in [f for f in filenames if producer.is_archive(f)]:
             yield dirpath, fname
 
 
 # LIMIT = 100
 LIMIT = None
 
 
 def compute_message_from(dirpath, filename):
     # filepath = os.path.join(dirpath, filename)
 
     version = producer.release_number(filename)
     print('|'.join(['', filename, version, '']))
 
 
 def produce_archive_messages(path):
     """From path, produce archive tarball message to celery.
 
     Args:
         path: top directory to list archives from.
 
     """
     limit = 0
     for dirpath, filename in list_archives_from(path):
         compute_message_from(dirpath, filename)
         if LIMIT and limit > LIMIT:
             return
         limit += 1
 
 
 produce_archive_messages(conf['mirror_root_directory'])