diff --git a/src/main/java/edu/ucla/library/avpairtree/Config.java b/src/main/java/edu/ucla/library/avpairtree/Config.java
index 7504fbe..c77caa6 100644
--- a/src/main/java/edu/ucla/library/avpairtree/Config.java
+++ b/src/main/java/edu/ucla/library/avpairtree/Config.java
@@ -66,6 +66,12 @@ public final class Config {
      */
     public static final String ACCESS_URL_PATTERN = "iiif.access.url";
 
+    /**
+     * The configuration property for which substitution pattern in iiif.access.url should be the ID; this is 1-based,
+     * not zero-based.
+     */
+    public static final String ACCESS_URL_ID_INDEX = "iiif.access.url.id.index";
+
     /**
      * The number of workers that should work to do media file conversions.
      */
diff --git a/src/main/java/edu/ucla/library/avpairtree/verticles/WatcherVerticle.java b/src/main/java/edu/ucla/library/avpairtree/verticles/WatcherVerticle.java
index 0469cf6..0ee077d 100644
--- a/src/main/java/edu/ucla/library/avpairtree/verticles/WatcherVerticle.java
+++ b/src/main/java/edu/ucla/library/avpairtree/verticles/WatcherVerticle.java
@@ -9,6 +9,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.csveed.api.CsvClient;
 import org.csveed.api.CsvClientImpl;
@@ -45,6 +47,8 @@ public class WatcherVerticle extends AbstractVerticle {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(WatcherVerticle.class, MessageCodes.BUNDLE);
 
+    private static final String SUBSTITUTION_PATTERN = "{}";
+
     @Override
     public void start(final Promise<Void> aPromise) {
         final DeliveryOptions options = new DeliveryOptions().setSendTimeout(Integer.MAX_VALUE);
@@ -152,7 +156,7 @@ private Future<String> updateCSV(final String aCsvFilePath, final Map<String, Cs
                         }
 
                         if (aArkMap.containsKey(ark)) {
-                            columns[columnCount] = encodeAccessURL(aArkMap.get(ark));
+                            columns[columnCount] = constructAccessURL(aArkMap.get(ark));
                         }
                     } else {
                         columns = new String[columnCount];
@@ -161,7 +165,7 @@ private Future<String> updateCSV(final String aCsvFilePath, final Map<String, Cs
                             if (accessUrlIndex != index) {
                                 columns[index] = row.get(index + 1); // Strangely, row is 1-based
                             } else if (aArkMap.containsKey(ark)) {
-                                columns[index] = encodeAccessURL(aArkMap.get(ark));
+                                columns[index] = constructAccessURL(aArkMap.get(ark));
                             }
                         }
                     }
@@ -194,25 +198,95 @@ private int getUrlAccessIndex(final Header aHeader) {
     }
 
     /**
-     * Encodes the Pairtree path for the A/V server's access URL.
+     * Encodes the Pairtree path in the A/V server's access URL.
      *
      * @param aCsvItem An item from the CSV file
      * @return An encoded path for the A/V server's access URL
+     * @throws IndexOutOfBoundsException If a supplied ID index position isn't valid
+     * @throws UnsupportedOperationException If the access URL pattern doesn't contain any placeholders
      */
-    private String encodeAccessURL(final CsvItem aCsvItem) {
+    private String constructAccessURL(final CsvItem aCsvItem)
+            throws IndexOutOfBoundsException, UnsupportedOperationException {
         final String arkPrefix = config().getString(Config.PAIRTREE_PREFIX);
         final String ark = aCsvItem.getItemARK();
         final String pathARK = ark.replace(arkPrefix, Constants.EMPTY); // Strip ARK prefix
         final String slug = aCsvItem.getPathRoot();
         final String encodedARK = PairtreeUtils.encodeID(ark);
         final String fileExt = Constants.PERIOD + config().getString(Config.ENCODING_FORMAT);
-        final String accessUrlPattern = config().getString(Config.ACCESS_URL_PATTERN, "{}");
+        final String accessUrlPattern = config().getString(Config.ACCESS_URL_PATTERN, SUBSTITUTION_PATTERN);
+        final int urlPatternIdIndex = config().getInteger(Config.ACCESS_URL_ID_INDEX, 1);
         final String ptPath = PairtreeUtils.mapToPtPath(slug + Constants.SLASH + Pairtree.ROOT, pathARK, pathARK);
-        final String ptFile = (ptPath + Constants.SLASH + encodedARK + fileExt).replace(Constants.PLUS, "%2B");
-        final String accessURL = StringUtils.format(accessUrlPattern, ptFile);
+        final String ptFilePath = (ptPath + Constants.SLASH + encodedARK + fileExt).replace(Constants.PLUS, "%2B");
+        final String accessURL = addIdPath(accessUrlPattern, urlPatternIdIndex, ptFilePath);
 
         LOGGER.debug(MessageCodes.AVPT_010, ark, accessURL);
 
         return accessURL;
     }
+
+    /**
+     * Gets the IIIF access URL.
+     *
+     * @param aAccessUrlPattern A textual pattern to use for the IIIF access URL
+     * @param aUrlPatternIdIndex A position for the ID in the access URL pattern
+     * @param aIdPath An ID's Pairtree path
+     * @return The IIIF access URL
+     * @throws IndexOutOfBoundsException If a supplied ID index position isn't valid
+     * @throws UnsupportedOperationException If the access URL pattern doesn't contain any placeholders
+     */
+    private String addIdPath(final String aAccessUrlPattern, final int aUrlPatternIdIndex, final String aIdPath)
+            throws IndexOutOfBoundsException, UnsupportedOperationException {
+        final int substitutionCount = countSubstitutionPatterns(aAccessUrlPattern);
+
+        // We allow up to three path substitutions, with the Pairtree path being able to be swapped into any of them
+        switch (substitutionCount) {
+            case 3:
+                if (aUrlPatternIdIndex == 1) {
+                    return StringUtils.format(aAccessUrlPattern, aIdPath, SUBSTITUTION_PATTERN, SUBSTITUTION_PATTERN);
+                } else if (aUrlPatternIdIndex == 2) {
+                    return StringUtils.format(aAccessUrlPattern, SUBSTITUTION_PATTERN, aIdPath, SUBSTITUTION_PATTERN);
+                } else if (aUrlPatternIdIndex == 3) {
+                    return StringUtils.format(aAccessUrlPattern, SUBSTITUTION_PATTERN, SUBSTITUTION_PATTERN, aIdPath);
+                } else {
+                    throw new IndexOutOfBoundsException(LOGGER.getMessage(MessageCodes.AVPT_013, aUrlPatternIdIndex));
+                }
+            case 2:
+                if (aUrlPatternIdIndex == 1) {
+                    return StringUtils.format(aAccessUrlPattern, aIdPath, SUBSTITUTION_PATTERN);
+                } else if (aUrlPatternIdIndex == 2) {
+                    return StringUtils.format(aAccessUrlPattern, SUBSTITUTION_PATTERN, aIdPath);
+                } else {
+                    throw new IndexOutOfBoundsException(LOGGER.getMessage(MessageCodes.AVPT_013, aUrlPatternIdIndex));
+                }
+            case 1:
+                if (aUrlPatternIdIndex == 1) {
+                    return StringUtils.format(aAccessUrlPattern, aIdPath);
+                } else {
+                    throw new IndexOutOfBoundsException(LOGGER.getMessage(MessageCodes.AVPT_013, aUrlPatternIdIndex));
+                }
+            default:
+                throw new UnsupportedOperationException(LOGGER.getMessage(MessageCodes.AVPT_013, substitutionCount));
+        }
+    }
+
+    /**
+     * Counts the number of substitution patterns in the supplied string.
+     *
+     * @param aString A string with substitution patterns (e.g. <code>{}</code>)
+     * @return The number of substitution patterns in the supplied string
+     */
+    private int countSubstitutionPatterns(final String aString) {
+        final Pattern pattern = Pattern.compile(SUBSTITUTION_PATTERN, Pattern.LITERAL);
+        final Matcher matcher = pattern.matcher(aString);
+
+        int startIndex = 0;
+        int count = 0;
+
+        while (matcher.find(startIndex)) {
+            startIndex = matcher.start() + 1;
+            count += 1;
+        }
+
+        return count;
+    }
 }
diff --git a/src/main/resources/av-pairtree_messages.xml b/src/main/resources/av-pairtree_messages.xml
index 9e39f8a..5421b58 100644
--- a/src/main/resources/av-pairtree_messages.xml
+++ b/src/main/resources/av-pairtree_messages.xml
@@ -17,5 +17,7 @@
   <entry key="AVPT_010">IIIF access URL created for '{}': {}</entry>
   <entry key="AVPT_011">{} worker starting in: {}</entry>
   <entry key="AVPT_012">{} worker pool size set to '{}' workers</entry>
+  <entry key="AVPT_013">Index for IIIF access URL doesn't correspond to number of substitution patterns: {}</entry>
+  <entry key="AVPT_014">IIIF access URL pattern doesn't contain a supported number of substitution patterns</entry>
 
 </properties>
diff --git a/src/test/java/edu/ucla/library/avpairtree/verticles/WatcherVerticleTest.java b/src/test/java/edu/ucla/library/avpairtree/verticles/WatcherVerticleTest.java
index 4cdb345..0e82051 100644
--- a/src/test/java/edu/ucla/library/avpairtree/verticles/WatcherVerticleTest.java
+++ b/src/test/java/edu/ucla/library/avpairtree/verticles/WatcherVerticleTest.java
@@ -136,7 +136,7 @@ private Future<Void> checkOutput(final String aFileName, final int aLatchCount,
             final AtomicInteger counter = new AtomicInteger(0);
 
             reader.lines().forEach(line -> {
-                if (line.contains(avServer)) {
+                if (line.contains(avServer) && line.contains(".mp4{}")) {
                     counter.incrementAndGet();
                 }
             });
diff --git a/src/test/resources/test-config.properties b/src/test/resources/test-config.properties
index 15a7d62..b8fbd39 100644
--- a/src/test/resources/test-config.properties
+++ b/src/test/resources/test-config.properties
@@ -20,8 +20,11 @@ audio.codec = aac
 audio.bit.rate = 320000
 audio.channels = 2
 
-# The URL pattern for our streaming A/V server
-iiif.access.url = https://wowza.library.ucla.edu/iiif_av_public/definst/mp4:{}/manifest.mpd
+# The URL pattern for our streaming A/V server; it can have up to three substitution patterns (i.e., "{}")
+iiif.access.url = https://wowza.library.ucla.edu/iiif_av_public/definst/mp4:{}{}
+
+# The 1-based position of the substitution pattern to use for the Pairtree path
+iiif.access.url.id.index = 1
 
 # The number of threads working on media file conversions
 conversion.workers = 2