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

[Gyan Doshi <ffmpeg@gyani.pro>]

On 2022-06-27 06:55 pm, Gyan Doshi wrote:
> Ping for the set.

Plan to push on Monday.

Regards,
Gyan

>
> On 2022-06-25 01:59 pm, Gyan Doshi wrote:
>> 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..8fc85d3a15 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" },
>
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