ffmpeg: add option -isync

This is a per-file input option that adjusts an input's timestamps
with reference to another input, so that emitted packet timestamps
account for the difference between the start times of the two inputs.

Typical use case is to sync two or more live inputs such as from capture
devices. Both the target and reference input source timestamps should be
based on the same clock source.

If either input lacks starting timestamps, then no sync adjustment is made.

1 files changed, 59 insertions, 0 deletions

diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index e08455478f..ac7fe3b27a 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 start_times_set = 1;
+
+        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 {
+            start_times_set = 0;
+        }
+
+        if (start_times_set) {
+            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" us to sync with Input #%d.\n", i, adjustment, self->input_sync_ref);
+        } else {
+            av_log(NULL, AV_LOG_INFO, "Unable to identify start times for Inputs #%d and %d both. No sync adjustment made.\n", i, self->input_sync_ref);
+        }
+    }
+
+    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" },