avdevice/decklink_dec: add option to align capture start time

This option is useful for maintaining input synchronization across N
different hardware devices deployed for 'N-way' redundancy.
The system time of different hardware devices should be synchronized
with protocols such as NTP or PTP, before using this option.

Signed-off-by: Marton Balint <cus@passwd.hu>

1 files changed, 10 insertions, 0 deletions

diff --git a/libavdevice/decklink_dec.cpp b/libavdevice/decklink_dec.cpp
index 7fabef231c..deb8f787ee 100644
--- a/libavdevice/decklink_dec.cpp
+++ b/libavdevice/decklink_dec.cpp
@@ -703,6 +703,16 @@ HRESULT decklink_input_callback::VideoInputFrameArrived(
         return S_OK;
     }
 
+    // Drop the frames till system's timestamp aligns with the configured value.
+    if (0 == ctx->frameCount && cctx->timestamp_align) {
+        AVRational remainder = av_make_q(av_gettime() % cctx->timestamp_align, 1000000);
+        AVRational frame_duration = av_inv_q(ctx->video_st->r_frame_rate);
+        if (av_cmp_q(remainder, frame_duration) > 0) {
+            ++ctx->dropped;
+            return S_OK;
+        }
+    }
+
     ctx->frameCount++;
     if (ctx->audio_pts_source == PTS_SRC_WALLCLOCK || ctx->video_pts_source == PTS_SRC_WALLCLOCK)
         wallclock = av_gettime_relative();