diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index d943f4d6f5..92dd584c89 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -518,6 +518,22 @@ see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1)
 Like the @code{-ss} option but relative to the "end of file". That is negative
 values are earlier in the file, 0 is at EOF.
 
+@item -isync @var{input_index} (@emph{input})
+Assign an input as a sync source.
+
+This will take the difference between the start times of the target and referenced inputs and
+offset the timestamps of the target file by that difference. The source timestamps of the two
+inputs should derive from the same clock source for expected results. If @code{copyts} is set
+then @code{start_at_zero} must also be set. If at least one of the inputs has no starting
+timestamp then the wallclock time at time of reception of the inputs is used as a best-effort
+sync basis.
+
+Acceptable values are those that refer to a valid ffmpeg input index. If the sync reference is
+the target index itself or @var{-1}, then no adjustment is made to target timestamps. A sync
+reference may not itself be synced to any other input.
+
+Default value is var{-1}.
+
 @item -itsoffset @var{offset} (@emph{input})
 Set the input time offset.
 
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index 69a368b8d1..dc74de6684 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -118,6 +118,7 @@ typedef struct OptionsContext {
     float readrate;
     int accurate_seek;
     int thread_queue_size;
+    int input_sync_ref;
 
     SpecifierOpt *ts_scale;
     int        nb_ts_scale;
@@ -410,6 +411,7 @@ typedef struct InputFile {
                              at the moment when looping happens */
     AVRational time_base; /* time base of the duration */
     int64_t input_ts_offset;
+    int input_sync_ref;
 
     int64_t ts_offset;
     int64_t last_ts;
diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index e08455478f..de858efbe9 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -235,6 +235,7 @@ static void init_options(OptionsContext *o)
     o->chapters_input_file = INT_MAX;
     o->accurate_seek  = 1;
     o->thread_queue_size = -1;
+    o->input_sync_ref = -1;
 }
 
 static int show_hwaccels(void *optctx, const char *opt, const char *arg)
@@ -287,6 +288,58 @@ static int parse_and_set_vsync(const char *arg, int *vsync_var, int file_idx, in
     return 0;
 }
 
+static int apply_sync_offsets(void)
+{
+    for (int i = 0; i < nb_input_files; i++) {
+        InputFile *ref, *self = input_files[i];
+        int64_t adjustment;
+        int64_t self_start_time, ref_start_time, self_seek_start, ref_seek_start;
+        int sync_fpw = 0;
+
+        if (self->input_sync_ref == -1 || self->input_sync_ref == i) continue;
+        if (self->input_sync_ref >= nb_input_files || self->input_sync_ref < -1) {
+            av_log(NULL, AV_LOG_FATAL, "-isync for input %d references non-existent input %d.\n", i, self->input_sync_ref);
+            exit_program(1);
+        }
+
+        if (copy_ts && !start_at_zero) {
+            av_log(NULL, AV_LOG_FATAL, "Use of -isync requires that start_at_zero be set if copyts is set.\n");
+            exit_program(1);
+        }
+
+        ref = input_files[self->input_sync_ref];
+        if (ref->input_sync_ref != -1 && ref->input_sync_ref != self->input_sync_ref) {
+            av_log(NULL, AV_LOG_ERROR, "-isync for input %d references a resynced input %d. Sync not set.\n", i, self->input_sync_ref);
+            continue;
+        }
+
+        if (self->ctx->start_time_realtime != AV_NOPTS_VALUE && ref->ctx->start_time_realtime != AV_NOPTS_VALUE) {
+            self_start_time = self->ctx->start_time_realtime;
+            ref_start_time  =  ref->ctx->start_time_realtime;
+        } else if (self->ctx->start_time != AV_NOPTS_VALUE && ref->ctx->start_time != AV_NOPTS_VALUE) {
+            self_start_time = self->ctx->start_time;
+            ref_start_time  =  ref->ctx->start_time;
+        } else {
+            self_start_time = self->ctx->first_pkt_wallclock;
+            ref_start_time  =  ref->ctx->first_pkt_wallclock;
+            sync_fpw = 1;
+        }
+
+        self_seek_start = self->start_time == AV_NOPTS_VALUE ? 0 : self->start_time;
+        ref_seek_start  =  ref->start_time == AV_NOPTS_VALUE ? 0 :  ref->start_time;
+
+        adjustment = (self_start_time - ref_start_time) + !copy_ts*(self_seek_start - ref_seek_start) + ref->input_ts_offset;
+
+        self->ts_offset += adjustment;
+
+        av_log(NULL, AV_LOG_INFO, "Adjusted ts offset for Input #%d by %"PRId64"d us to sync with Input #%d", i, adjustment, self->input_sync_ref);
+        if (sync_fpw) av_log(NULL, AV_LOG_INFO, " using reception wallclock time. Sync may not be obtained");
+        av_log(NULL, AV_LOG_INFO, ".\n");
+    }
+
+    return 0;
+}
+
 static int opt_filter_threads(void *optctx, const char *opt, const char *arg)
 {
     av_free(filter_nbthreads);
@@ -1305,6 +1358,7 @@ static int open_input_file(OptionsContext *o, const char *filename)
     f->ist_index  = nb_input_streams - ic->nb_streams;
     f->start_time = o->start_time;
     f->recording_time = o->recording_time;
+    f->input_sync_ref = o->input_sync_ref;
     f->input_ts_offset = o->input_ts_offset;
     f->ts_offset  = o->input_ts_offset - (copy_ts ? (start_at_zero && ic->start_time != AV_NOPTS_VALUE ? ic->start_time : 0) : timestamp);
     f->nb_streams = ic->nb_streams;
@@ -3489,6 +3543,8 @@ int ffmpeg_parse_options(int argc, char **argv)
         goto fail;
     }
 
+    apply_sync_offsets();
+
     /* create the complex filtergraphs */
     ret = init_complex_filters();
     if (ret < 0) {
@@ -3603,6 +3659,9 @@ const OptionDef options[] = {
     { "accurate_seek",  OPT_BOOL | OPT_OFFSET | OPT_EXPERT |
                         OPT_INPUT,                                   { .off = OFFSET(accurate_seek) },
         "enable/disable accurate seeking with -ss" },
+    { "isync",          HAS_ARG | OPT_INT | OPT_OFFSET |
+                        OPT_EXPERT | OPT_INPUT,                      { .off = OFFSET(input_sync_ref) },
+        "Indicate the input index for sync reference", "sync ref" },
     { "itsoffset",      HAS_ARG | OPT_TIME | OPT_OFFSET |
                         OPT_EXPERT | OPT_INPUT,                      { .off = OFFSET(input_ts_offset) },
         "set the input ts offset", "time_off" },
