On Mon, 24 Sep 2018, Karthick J wrote:
From: Karthick Jeyapal <kjeya...@akamai.com>
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.
Here is a review of the patch if you want to proceed with implementing
the feature in decklink. The introduced code can be simple/small enough
that I think it is OK to include it if you prefer that.
---
doc/indevs.texi | 10 ++++++++++
libavdevice/decklink_common_c.h | 1 +
libavdevice/decklink_dec.cpp | 20 ++++++++++++++++++++
libavdevice/decklink_dec_c.c | 1 +
4 files changed, 32 insertions(+)
diff --git a/doc/indevs.texi b/doc/indevs.texi
index ed2784b..dfd530a 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -371,6 +371,16 @@ If set to @option{true}, timestamps are forwarded as they
are without removing
the initial offset.
Defaults to @option{false}.
+@item timestamp_align
+Capture start time alignment in seconds. If set to nonzero, input frames are
+dropped till the system timestamp aligns with configured value.
+Alignment difference of upto one frame duration is tolerated.
+This 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.
+Defaults to @samp{0}.
This approach is not perfect. If frame callbacks are roughly at the same
time as the alignment, then - because of the jitter of the callbacks -
segments can be skipped or 1 frame difference is possible. At least
mention this in the docs.
Also I remember having some burst callbacks in case of signal
loss/return on newer DeckLink models, that might mess this up as well.
An always working synchornization method probably needs a continous SDI
timecode which is unfortunately not an option in most cases.
+
@end table
@subsection Examples
diff --git a/libavdevice/decklink_common_c.h b/libavdevice/decklink_common_c.h
index 32a5d70..c4a8985 100644
--- a/libavdevice/decklink_common_c.h
+++ b/libavdevice/decklink_common_c.h
@@ -56,6 +56,7 @@ struct decklink_cctx {
int raw_format;
int64_t queue_size;
int copyts;
+ int timestamp_align;
Make this int64_t and the option below AV_OPT_TYPE_DURATION.
};
#endif /* AVDEVICE_DECKLINK_COMMON_C_H */
diff --git a/libavdevice/decklink_dec.cpp b/libavdevice/decklink_dec.cpp
index 7fabef2..24f5ca9 100644
--- a/libavdevice/decklink_dec.cpp
+++ b/libavdevice/decklink_dec.cpp
@@ -703,6 +703,26 @@ 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) {
+ int64_t current_time_us = av_gettime();
+ int64_t align_factor_us = (cctx->timestamp_align * 1000000);
+ int remainder = current_time_us % align_factor_us;
+ if (videoFrame) {
+ videoFrame->GetStreamTime(&frameTime, &frameDuration, 1000000);
+ } else if (audioFrame) {
+ long sample_count = audioFrame->GetSampleFrameCount();
+ frameDuration = (long)(sample_count * 1000000) /
bmdAudioSampleRate48kHz;
+ } else {
+ frameDuration = 0;
+ }
+ // threshold of one frameDuration
+ if(remainder > frameDuration) {
+ ++ctx->dropped;
+ return S_OK;
+ }
You already know the frame rate, so I'd simply write something like:
if (ctx->frameCount == 0 && ctx->timestamp_align) {
AVRational remainder = av_make_q(av_gettime() % cctx->timestamp_align,
1000000);
if (av_cmp_q(remainder, st->video_st->time_base) > 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();
diff --git a/libavdevice/decklink_dec_c.c b/libavdevice/decklink_dec_c.c
index 6ab3819..bef9c14 100644
--- a/libavdevice/decklink_dec_c.c
+++ b/libavdevice/decklink_dec_c.c
@@ -84,6 +84,7 @@ static const AVOption options[] = {
{ "queue_size", "input queue buffer size", OFFSET(queue_size),
AV_OPT_TYPE_INT64, { .i64 = (1024 * 1024 * 1024)}, 0, INT64_MAX, DEC },
{ "audio_depth", "audio bitdepth (16 or 32)", OFFSET(audio_depth),
AV_OPT_TYPE_INT, { .i64 = 16}, 16, 32, DEC },
{ "decklink_copyts", "copy timestamps, do not remove the initial offset",
OFFSET(copyts), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, DEC },
+ { "timestamp_align", "Capture start time alignment (in seconds)",
OFFSET(timestamp_align), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, DEC },
AV_OPT_TYPE_DURATION.
Regards,
Marton
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