Lip sync.

[G4EWJ]

A week or so ago on the QO-100 chat, someone (I think it was that station who's a really good singer) asked if it was possible to change lip sync in real time. You shouldn't really be able to take liberties like changing the timings in a transport stream, but it does seem to be practical.

I've written a test program which accepts a UDP TS, modifies the presentation time stamps (PTS) in the audio stream and sends the TS onwards. The time difference applied to the audio PTS's can be changed on the fly from the keyboard.

The video stream also has PTS's, which are not changed. The PTS's are relative to the program clock reference (PCR) which is the master clock embedded in the TS. VLC uses the PCR and the audio and video PTS's to know when to render them.

The question is, is the program practical to use in this form? I'm not familiar with OBS / DATVEasy / Pluto setups. Is there a point in the system where a UDP TS can be directed to an IP address? I believe that different setups can send IQ data or TS to the Pluto, so only the latter would be practical.

VLC copes quite well. Whenever a change is made to the audio timing, it keeps the video going and the audio re-appears in a second or two. MPV is less elegant and there can be a second or two of video stop,slow,quick.

Brian
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[PE5PVB]

Nice solution, best solution should be a PCR lock in ffmpeg ofcourse.

[G4EWJ]

Can you define PCR lock please.

Brian

[Basil]

It was I who asked, and I watch this with great interest, the coder who manages to allow lip sync changes in real time gets my rapturous applause, I think it would be one of the most useful pieces of software that I can imagine for DATV. Fiddling about and retatrting aapplications to see the effects of changes is surely something 2023 could relegate to the past?

Thanks for taking his on board Brian, bravo!

(I am a truly appalling singer, and I am also a bloke, but Sally who I sometimes TX songs from is quite the opposite, but probably far too modest to say so).

[G4EWJ]

>>I am a truly appalling singer
Join the club.

I've just been watching the GB3SQ stream. G4KLB was testing the latest version of OBS (29.1?) and was able to change the lip sync on the fly. Is that a new feature, or can the lip sync be changed somewhere else in the system, or is it only OBS that can do lip sync on the fly?

Brian