Quoting Gyan Doshi (2022-07-11 08:46:48) > > > On 2022-07-11 12:21 am, Anton Khirnov wrote: > > Quoting Gyan Doshi (2022-07-10 20:02:38) > >> > >> On 2022-07-10 10:46 pm, Anton Khirnov wrote: > >>> Quoting Gyan Doshi (2022-07-08 05:56:21) > >>>> On 2022-07-07 03:11 pm, Anton Khirnov wrote: > >>>>> Quoting Gyan Doshi (2022-07-04 18:29:12) > >>>>>> 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. FFmpeg must have been compiled with > >>>>>> thread support for this last case. > >>>>> I'm wondering if simply using the other input's InputFile.ts_offset > >>>>> wouldn't achieve the same effect with much less complexity. > >>>> That's what I initially did. But since the code can also use two other > >>>> sources for start times (start_time_realtime, first_pkt_wallclock), > >>>> those intervals may not exactly match the difference between > >>>> fmctx->start_times so I use a generic calculation. > >>> In what cases is it better to use either of those two other sources? > >>> > >>> As per the commit message, the timestamps of both inputs are supposed to > >>> come from the same clock. Then it seems to me that offsetting each of > >>> those streams by different amounts would break synchronization rather > >>> than improve it. > >> The first preference, when available, stores the epoch time closest to > >> time of capture. That would eliminate some jitter. > >> The 2nd preference is the fmctx->start_time. The 3rd is the reception > >> wallclock. It is a fallback. It will likely lead to the worst sync. > > You did not answer my question. > > If both streams use the same clock, then how is offsetting them by > > different amounts improve sync? > > Because the clocks can be different at different stages of stream > conveyance i.e. capture -> encode -> network relay -> ffmpeg reception. > As long as both use the same clock at a given stage, they represent the > same sync relation but with some jitter in the mix added with each stage.
Why would you send the streams separately and not synchronized before network transmission? -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
