diff --git a/tools/ismindex.c b/tools/ismindex.c
index 64dc268d54..57a909e9b0 100644
--- a/tools/ismindex.c
+++ b/tools/ismindex.c
@@ -34,6 +34,11 @@
  * ismindex -split foo.ismv
  * This step creates a file Manifest and directories QualityLevel(...),
  * that can be read directly by a smooth streaming player.
+ *
+ * The -output dir option can be used to request that output files
+ * (both .ism/.ismc, or Manifest/QualityLevels* when splitting)
+ * should be written to this directory instead of in the current directory.
+ * (The directory itself isn't created if it doesn't already exist.)
  */
 
 #include <stdio.h>
@@ -49,7 +54,7 @@
 static int usage(const char *argv0, int ret)
 {
     fprintf(stderr, "%s [-split] [-n basename] [-path-prefix prefix] "
-                    "[-ismc-prefix prefix] file1 [file2] ...\n", argv0);
+                    "[-ismc-prefix prefix] [-output dir] file1 [file2] ...\n", argv0);
     return ret;
 }
 
@@ -124,15 +129,15 @@ static int write_fragment(const char *filename, AVIOContext *in)
 }
 
 static int write_fragments(struct Tracks *tracks, int start_index,
-                           AVIOContext *in)
+                           AVIOContext *in, const char *output_prefix)
 {
-    char dirname[100], filename[500];
+    char dirname[2048], filename[2048];
     int i, j;
 
     for (i = start_index; i < tracks->nb_tracks; i++) {
         struct Track *track = tracks->tracks[i];
         const char *type    = track->is_video ? "video" : "audio";
-        snprintf(dirname, sizeof(dirname), "QualityLevels(%d)", track->bitrate);
+        snprintf(dirname, sizeof(dirname), "%sQualityLevels(%d)", output_prefix, track->bitrate);
         if (mkdir(dirname, 0777) == -1)
             return AVERROR(errno);
         for (j = 0; j < track->chunks; j++) {
@@ -202,7 +207,7 @@ fail:
 }
 
 static int read_mfra(struct Tracks *tracks, int start_index,
-                     const char *file, int split)
+                     const char *file, int split, const char *output_prefix)
 {
     int err = 0;
     AVIOContext *f = NULL;
@@ -226,7 +231,7 @@ static int read_mfra(struct Tracks *tracks, int start_index,
     }
 
     if (split)
-        err = write_fragments(tracks, start_index, f);
+        err = write_fragments(tracks, start_index, f, output_prefix);
 
 fail:
     if (f)
@@ -278,7 +283,8 @@ fail:
     return err;
 }
 
-static int handle_file(struct Tracks *tracks, const char *file, int split)
+static int handle_file(struct Tracks *tracks, const char *file, int split,
+                       const char *output_prefix)
 {
     AVFormatContext *ctx = NULL;
     int err = 0, i, orig_tracks = tracks->nb_tracks;
@@ -380,7 +386,7 @@ static int handle_file(struct Tracks *tracks, const char *file, int split)
 
     avformat_close_input(&ctx);
 
-    err = read_mfra(tracks, orig_tracks, file, split);
+    err = read_mfra(tracks, orig_tracks, file, split, output_prefix);
 
 fail:
     if (ctx)
@@ -388,15 +394,16 @@ fail:
     return err;
 }
 
-static void output_server_manifest(struct Tracks *tracks,
-                                   const char *basename, const char *path_prefix,
+static void output_server_manifest(struct Tracks *tracks, const char *basename,
+                                   const char *output_prefix,
+                                   const char *path_prefix,
                                    const char *ismc_prefix)
 {
     char filename[1000];
     FILE *out;
     int i;
 
-    snprintf(filename, sizeof(filename), "%s.ism", basename);
+    snprintf(filename, sizeof(filename), "%s%s.ism", output_prefix, basename);
     out = fopen(filename, "w");
     if (!out) {
         perror(filename);
@@ -442,17 +449,17 @@ static void print_track_chunks(FILE *out, struct Tracks *tracks, int main,
     }
 }
 
-static void output_client_manifest(struct Tracks *tracks,
-                                   const char *basename, int split)
+static void output_client_manifest(struct Tracks *tracks, const char *basename,
+                                   const char *output_prefix, int split)
 {
     char filename[1000];
     FILE *out;
     int i, j;
 
     if (split)
-        snprintf(filename, sizeof(filename), "Manifest");
+        snprintf(filename, sizeof(filename), "%sManifest", output_prefix);
     else
-        snprintf(filename, sizeof(filename), "%s.ismc", basename);
+        snprintf(filename, sizeof(filename), "%s%s.ismc", output_prefix, basename);
     out = fopen(filename, "w");
     if (!out) {
         perror(filename);
@@ -541,6 +548,8 @@ int main(int argc, char **argv)
 {
     const char *basename = NULL;
     const char *path_prefix = "", *ismc_prefix = "";
+    const char *output_prefix = "";
+    char output_prefix_buf[2048];
     int split = 0, i;
     struct Tracks tracks = { 0, .video_track = -1, .audio_track = -1 };
 
@@ -556,12 +565,20 @@ int main(int argc, char **argv)
         } else if (!strcmp(argv[i], "-ismc-prefix")) {
             ismc_prefix = argv[i + 1];
             i++;
+        } else if (!strcmp(argv[i], "-output")) {
+            output_prefix = argv[i + 1];
+            i++;
+            if (output_prefix[strlen(output_prefix) - 1] != '/') {
+                snprintf(output_prefix_buf, sizeof(output_prefix_buf),
+                         "%s/", output_prefix);
+                output_prefix = output_prefix_buf;
+            }
         } else if (!strcmp(argv[i], "-split")) {
             split = 1;
         } else if (argv[i][0] == '-') {
             return usage(argv[0], 1);
         } else {
-            if (handle_file(&tracks, argv[i], split))
+            if (handle_file(&tracks, argv[i], split, output_prefix))
                 return 1;
         }
     }
@@ -569,8 +586,9 @@ int main(int argc, char **argv)
         return usage(argv[0], 1);
 
     if (!split)
-        output_server_manifest(&tracks, basename, path_prefix, ismc_prefix);
-    output_client_manifest(&tracks, basename, split);
+        output_server_manifest(&tracks, basename, output_prefix,
+                               path_prefix, ismc_prefix);
+    output_client_manifest(&tracks, basename, output_prefix, split);
 
     clean_tracks(&tracks);