[FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

Stores wallclock time for the first packet received.
Used for crude sync offset among inputs.
---
 doc/APIchanges         |  3 +++
 libavformat/avformat.h | 10 ++++++++++
 libavformat/demux.c    |  3 +++
 libavformat/options.c  |  1 +
 libavformat/version.h  |  2 +-
 5 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 20b944933a..94c53d283f 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -14,6 +14,9 @@ libavutil:     2021-04-27
 
 API changes, most recent first:
 
+2022-06-xx - xxxxxxxxxx - lavf 59.26.100 - avformat.h
+  Add and set AVFormatContext.first_pkt_wallclock field.
+
 2022-06-12 - xxxxxxxxxx - lavf 59.25.100 - avio.h
   Add avio_vprintf(), similar to avio_printf() but allow to use it
   from within a function taking a variable argument list as input.
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f12fa7d904..a45777ab39 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1808,6 +1808,16 @@ typedef struct AVFormatContext {
      */
     int max_probe_packets;
 
+    /**
+     * Wallclock start time of the stream in real world time, in microseconds
+     * since the Unix epoch (00:00 1st January 1970). That is, the first packet
+     * was received at this real world time.
+     * - demuxing: Set by libavformat. Users may want to use start_time_realtime
+     *             if set.
+     * - muxing: unused.
+     */
+    int64_t first_pkt_wallclock;
+
     /**
      * A callback for closing the streams opened with AVFormatContext.io_open().
      *
diff --git a/libavformat/demux.c b/libavformat/demux.c
index e121253dfd..7e0540debf 100644
--- a/libavformat/demux.c
+++ b/libavformat/demux.c
@@ -628,6 +628,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
 
         force_codec_ids(s, st);
 
+        if (s->first_pkt_wallclock == AV_NOPTS_VALUE)
+            s->first_pkt_wallclock = av_gettime();
+
         /* TODO: audio: time filter; video: frame reordering (pts != dts) */
         if (s->use_wallclock_as_timestamps)
             pkt->dts = pkt->pts = av_rescale_q(av_gettime(), AV_TIME_BASE_Q, st->time_base);
diff --git a/libavformat/options.c b/libavformat/options.c
index 0079a06d9a..77d4dfd1d0 100644
--- a/libavformat/options.c
+++ b/libavformat/options.c
@@ -184,6 +184,7 @@ AVFormatContext *avformat_alloc_context(void)
         return NULL;
     }
 
+    s->first_pkt_wallclock = AV_NOPTS_VALUE;
     si->shortest_end = AV_NOPTS_VALUE;
 
     return s;
diff --git a/libavformat/version.h b/libavformat/version.h
index 966ebb7ed3..0708d619c0 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,7 +31,7 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR  25
+#define LIBAVFORMAT_VERSION_MINOR  26
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
-- 
2.36.1

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[FFmpeg-devel] [PATCH v2 2/2] ffmpeg: add option -isync

[Gyan Doshi]

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 not all inputs have timestamps, the wallclock times at the time of
reception of inputs shall be used.
---
 doc/ffmpeg.texi      | 16 ++++++++++++
 fftools/ffmpeg.h     |  2 ++
 fftools/ffmpeg_opt.c | 59 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)

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" },
-- 
2.36.1

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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

On 2022-07-04 10:12 am, Anton Khirnov wrote:
> Quoting Gyan Doshi (2022-07-02 11:51:49)
>>
>> On 2022-07-02 02:12 pm, Anton Khirnov wrote:
>>> Quoting Gyan Doshi (2022-07-01 13:07:13)
>>>> On 2022-07-01 03:20 pm, Anton Khirnov wrote:
>>>>> Quoting Gyan Doshi (2022-06-28 08:40:58)
>>>>>> On 2022-06-28 10:43 am, Anton Khirnov wrote:
>>>>>>> Quoting Gyan Doshi (2022-06-25 10:29:50)
>>>>>>>> Stores wallclock time for the first packet received.
>>>>>>>> Used for crude sync offset among inputs.
>>>>>>>> ---
>>>>>>>>      doc/APIchanges         |  3 +++
>>>>>>>>      libavformat/avformat.h | 10 ++++++++++
>>>>>>>>      libavformat/demux.c    |  3 +++
>>>>>>>>      libavformat/options.c  |  1 +
>>>>>>>>      libavformat/version.h  |  2 +-
>>>>>>>>      5 files changed, 18 insertions(+), 1 deletion(-)
>>>>>>> Why should this be in the library? Seems to me this can be just as
>>>>>>> easily done by the callers who need it.
>>>>>> To not add some extra latency,  just like how
>>>>>> `use_wallclock_as_timestamps` was implemented inside lavf.
>>>>> Where would that extra latency come from?
>>>> The interval between its current assigment inside ff_read_packet() and
>>>> the chance for assignment in process_input() in ffmpeg.c
>>> And why would there be a significant delay there?
>> With multiple inputs, get_input_packet_mt() will populate each input
>> queue in async whereas process_input() will be called on that input at
>> best in a round robin fashion depending on choose_output().
> So why should this information not be set by get_input_packet_mt() then?

It can. I wanted to avoid all the latency I could. But I can shift it 
there. Will do.

Regards,
Gyan
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Anton Khirnov]

Quoting Gyan Doshi (2022-07-02 11:51:49)
> 
> 
> On 2022-07-02 02:12 pm, Anton Khirnov wrote:
> > Quoting Gyan Doshi (2022-07-01 13:07:13)
> >>
> >> On 2022-07-01 03:20 pm, Anton Khirnov wrote:
> >>> Quoting Gyan Doshi (2022-06-28 08:40:58)
> >>>> On 2022-06-28 10:43 am, Anton Khirnov wrote:
> >>>>> Quoting Gyan Doshi (2022-06-25 10:29:50)
> >>>>>> Stores wallclock time for the first packet received.
> >>>>>> Used for crude sync offset among inputs.
> >>>>>> ---
> >>>>>>     doc/APIchanges         |  3 +++
> >>>>>>     libavformat/avformat.h | 10 ++++++++++
> >>>>>>     libavformat/demux.c    |  3 +++
> >>>>>>     libavformat/options.c  |  1 +
> >>>>>>     libavformat/version.h  |  2 +-
> >>>>>>     5 files changed, 18 insertions(+), 1 deletion(-)
> >>>>> Why should this be in the library? Seems to me this can be just as
> >>>>> easily done by the callers who need it.
> >>>> To not add some extra latency,  just like how
> >>>> `use_wallclock_as_timestamps` was implemented inside lavf.
> >>> Where would that extra latency come from?
> >> The interval between its current assigment inside ff_read_packet() and
> >> the chance for assignment in process_input() in ffmpeg.c
> > And why would there be a significant delay there?
> 
> With multiple inputs, get_input_packet_mt() will populate each input 
> queue in async whereas process_input() will be called on that input at 
> best in a round robin fashion depending on choose_output().

So why should this information not be set by get_input_packet_mt() then?

-- 
Anton Khirnov
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

On 2022-07-02 02:12 pm, Anton Khirnov wrote:
> Quoting Gyan Doshi (2022-07-01 13:07:13)
>>
>> On 2022-07-01 03:20 pm, Anton Khirnov wrote:
>>> Quoting Gyan Doshi (2022-06-28 08:40:58)
>>>> On 2022-06-28 10:43 am, Anton Khirnov wrote:
>>>>> Quoting Gyan Doshi (2022-06-25 10:29:50)
>>>>>> Stores wallclock time for the first packet received.
>>>>>> Used for crude sync offset among inputs.
>>>>>> ---
>>>>>>     doc/APIchanges         |  3 +++
>>>>>>     libavformat/avformat.h | 10 ++++++++++
>>>>>>     libavformat/demux.c    |  3 +++
>>>>>>     libavformat/options.c  |  1 +
>>>>>>     libavformat/version.h  |  2 +-
>>>>>>     5 files changed, 18 insertions(+), 1 deletion(-)
>>>>> Why should this be in the library? Seems to me this can be just as
>>>>> easily done by the callers who need it.
>>>> To not add some extra latency,  just like how
>>>> `use_wallclock_as_timestamps` was implemented inside lavf.
>>> Where would that extra latency come from?
>> The interval between its current assigment inside ff_read_packet() and
>> the chance for assignment in process_input() in ffmpeg.c
> And why would there be a significant delay there?

With multiple inputs, get_input_packet_mt() will populate each input 
queue in async whereas process_input() will be called on that input at 
best in a round robin fashion depending on choose_output().

Regards,
Gyan

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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Anton Khirnov]

Quoting Gyan Doshi (2022-07-01 13:07:13)
> 
> 
> On 2022-07-01 03:20 pm, Anton Khirnov wrote:
> > Quoting Gyan Doshi (2022-06-28 08:40:58)
> >>
> >> On 2022-06-28 10:43 am, Anton Khirnov wrote:
> >>> Quoting Gyan Doshi (2022-06-25 10:29:50)
> >>>> Stores wallclock time for the first packet received.
> >>>> Used for crude sync offset among inputs.
> >>>> ---
> >>>>    doc/APIchanges         |  3 +++
> >>>>    libavformat/avformat.h | 10 ++++++++++
> >>>>    libavformat/demux.c    |  3 +++
> >>>>    libavformat/options.c  |  1 +
> >>>>    libavformat/version.h  |  2 +-
> >>>>    5 files changed, 18 insertions(+), 1 deletion(-)
> >>> Why should this be in the library? Seems to me this can be just as
> >>> easily done by the callers who need it.
> >> To not add some extra latency,  just like how
> >> `use_wallclock_as_timestamps` was implemented inside lavf.
> > Where would that extra latency come from?
> 
> The interval between its current assigment inside ff_read_packet() and 
> the chance for assignment in process_input() in ffmpeg.c

And why would there be a significant delay there?

-- 
Anton Khirnov
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

On 2022-07-01 03:20 pm, Anton Khirnov wrote:
> Quoting Gyan Doshi (2022-06-28 08:40:58)
>>
>> On 2022-06-28 10:43 am, Anton Khirnov wrote:
>>> Quoting Gyan Doshi (2022-06-25 10:29:50)
>>>> Stores wallclock time for the first packet received.
>>>> Used for crude sync offset among inputs.
>>>> ---
>>>>    doc/APIchanges         |  3 +++
>>>>    libavformat/avformat.h | 10 ++++++++++
>>>>    libavformat/demux.c    |  3 +++
>>>>    libavformat/options.c  |  1 +
>>>>    libavformat/version.h  |  2 +-
>>>>    5 files changed, 18 insertions(+), 1 deletion(-)
>>> Why should this be in the library? Seems to me this can be just as
>>> easily done by the callers who need it.
>> To not add some extra latency,  just like how
>> `use_wallclock_as_timestamps` was implemented inside lavf.
> Where would that extra latency come from?

The interval between its current assigment inside ff_read_packet() and 
the chance for assignment in process_input() in ffmpeg.c

Regards,
Gyan
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Anton Khirnov]

Quoting Gyan Doshi (2022-06-28 08:40:58)
> 
> 
> On 2022-06-28 10:43 am, Anton Khirnov wrote:
> > Quoting Gyan Doshi (2022-06-25 10:29:50)
> >> Stores wallclock time for the first packet received.
> >> Used for crude sync offset among inputs.
> >> ---
> >>   doc/APIchanges         |  3 +++
> >>   libavformat/avformat.h | 10 ++++++++++
> >>   libavformat/demux.c    |  3 +++
> >>   libavformat/options.c  |  1 +
> >>   libavformat/version.h  |  2 +-
> >>   5 files changed, 18 insertions(+), 1 deletion(-)
> > Why should this be in the library? Seems to me this can be just as
> > easily done by the callers who need it.
> 
> To not add some extra latency,  just like how 
> `use_wallclock_as_timestamps` was implemented inside lavf.

Where would that extra latency come from?
I see no reason for use_wallclock_as_timestamps to exist either, it can
just as well be used from ffmpeg.c or whatever caller needs it.

-- 
Anton Khirnov
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

On 2022-06-28 01:20 pm, Andreas Rheinhardt wrote:
> Gyan Doshi:
>>
>> On 2022-06-28 10:43 am, Anton Khirnov wrote:
>>> Quoting Gyan Doshi (2022-06-25 10:29:50)
>>>> Stores wallclock time for the first packet received.
>>>> Used for crude sync offset among inputs.
>>>> ---
>>>>    doc/APIchanges         |  3 +++
>>>>    libavformat/avformat.h | 10 ++++++++++
>>>>    libavformat/demux.c    |  3 +++
>>>>    libavformat/options.c  |  1 +
>>>>    libavformat/version.h  |  2 +-
>>>>    5 files changed, 18 insertions(+), 1 deletion(-)
>>> Why should this be in the library? Seems to me this can be just as
>>> easily done by the callers who need it.
>> To not add some extra latency,  just like how
>> `use_wallclock_as_timestamps` was implemented inside lavf.
>>
> Why don't you use use_wallclock_as_timestamps and offset the timestamps
> by the lowest returned timestamp?

Because that will destroy the original inter-packet timing intervals. 
Those we usually wish to keep, especially for B-frames which are stored 
out of presentation order.

Regards,
Gyan
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Andreas Rheinhardt]

Gyan Doshi:
> 
> 
> On 2022-06-28 10:43 am, Anton Khirnov wrote:
>> Quoting Gyan Doshi (2022-06-25 10:29:50)
>>> Stores wallclock time for the first packet received.
>>> Used for crude sync offset among inputs.
>>> ---
>>>   doc/APIchanges         |  3 +++
>>>   libavformat/avformat.h | 10 ++++++++++
>>>   libavformat/demux.c    |  3 +++
>>>   libavformat/options.c  |  1 +
>>>   libavformat/version.h  |  2 +-
>>>   5 files changed, 18 insertions(+), 1 deletion(-)
>> Why should this be in the library? Seems to me this can be just as
>> easily done by the callers who need it.
> 
> To not add some extra latency,  just like how
> `use_wallclock_as_timestamps` was implemented inside lavf.
> 

Why don't you use use_wallclock_as_timestamps and offset the timestamps
by the lowest returned timestamp?

- Andreas
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

On 2022-06-28 10:43 am, Anton Khirnov wrote:
> Quoting Gyan Doshi (2022-06-25 10:29:50)
>> Stores wallclock time for the first packet received.
>> Used for crude sync offset among inputs.
>> ---
>>   doc/APIchanges         |  3 +++
>>   libavformat/avformat.h | 10 ++++++++++
>>   libavformat/demux.c    |  3 +++
>>   libavformat/options.c  |  1 +
>>   libavformat/version.h  |  2 +-
>>   5 files changed, 18 insertions(+), 1 deletion(-)
> Why should this be in the library? Seems to me this can be just as
> easily done by the callers who need it.

To not add some extra latency,  just like how 
`use_wallclock_as_timestamps` was implemented inside lavf.

Regards,
Gyan
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Re: [FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Anton Khirnov]

Quoting Gyan Doshi (2022-06-25 10:29:50)
> Stores wallclock time for the first packet received.
> Used for crude sync offset among inputs.
> ---
>  doc/APIchanges         |  3 +++
>  libavformat/avformat.h | 10 ++++++++++
>  libavformat/demux.c    |  3 +++
>  libavformat/options.c  |  1 +
>  libavformat/version.h  |  2 +-
>  5 files changed, 18 insertions(+), 1 deletion(-)

Why should this be in the library? Seems to me this can be just as
easily done by the callers who need it.

-- 
Anton Khirnov
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[FFmpeg-devel] [PATCH v2 1/2] avformat: add AVFormatContext.first_pkt_wallclock

[Gyan Doshi]

Stores wallclock time for the first packet received.
Used for crude sync offset among inputs.
---
 doc/APIchanges         |  3 +++
 libavformat/avformat.h | 10 ++++++++++
 libavformat/demux.c    |  3 +++
 libavformat/options.c  |  1 +
 libavformat/version.h  |  2 +-
 5 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 20b944933a..94c53d283f 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -14,6 +14,9 @@ libavutil:     2021-04-27
 
 API changes, most recent first:
 
+2022-06-xx - xxxxxxxxxx - lavf 59.26.100 - avformat.h
+  Add and set AVFormatContext.first_pkt_wallclock field.
+
 2022-06-12 - xxxxxxxxxx - lavf 59.25.100 - avio.h
   Add avio_vprintf(), similar to avio_printf() but allow to use it
   from within a function taking a variable argument list as input.
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f12fa7d904..a45777ab39 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1808,6 +1808,16 @@ typedef struct AVFormatContext {
      */
     int max_probe_packets;
 
+    /**
+     * Wallclock start time of the stream in real world time, in microseconds
+     * since the Unix epoch (00:00 1st January 1970). That is, the first packet
+     * was received at this real world time.
+     * - demuxing: Set by libavformat. Users may want to use start_time_realtime
+     *             if set.
+     * - muxing: unused.
+     */
+    int64_t first_pkt_wallclock;
+
     /**
      * A callback for closing the streams opened with AVFormatContext.io_open().
      *
diff --git a/libavformat/demux.c b/libavformat/demux.c
index e121253dfd..7e0540debf 100644
--- a/libavformat/demux.c
+++ b/libavformat/demux.c
@@ -628,6 +628,9 @@ FF_ENABLE_DEPRECATION_WARNINGS
 
         force_codec_ids(s, st);
 
+        if (s->first_pkt_wallclock == AV_NOPTS_VALUE)
+            s->first_pkt_wallclock = av_gettime();
+
         /* TODO: audio: time filter; video: frame reordering (pts != dts) */
         if (s->use_wallclock_as_timestamps)
             pkt->dts = pkt->pts = av_rescale_q(av_gettime(), AV_TIME_BASE_Q, st->time_base);
diff --git a/libavformat/options.c b/libavformat/options.c
index 0079a06d9a..77d4dfd1d0 100644
--- a/libavformat/options.c
+++ b/libavformat/options.c
@@ -184,6 +184,7 @@ AVFormatContext *avformat_alloc_context(void)
         return NULL;
     }
 
+    s->first_pkt_wallclock = AV_NOPTS_VALUE;
     si->shortest_end = AV_NOPTS_VALUE;
 
     return s;
diff --git a/libavformat/version.h b/libavformat/version.h
index 966ebb7ed3..0708d619c0 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,7 +31,7 @@
 
 #include "version_major.h"
 
-#define LIBAVFORMAT_VERSION_MINOR  25
+#define LIBAVFORMAT_VERSION_MINOR  26
 #define LIBAVFORMAT_VERSION_MICRO 100
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
-- 
2.36.1

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