On 09/11/2025 17.45, hydra3333 via ffmpeg-user wrote:
>> From: Mark Filipak via ffmpeg-user <[email protected]>
>> Sent: Monday, November 10, 2025 7:06 AM
>> Hi Gerd, I'm guessing you have an unclean source. FFmpeg can clean
>> unclean sources, but sometimes FFmpeg makes things worse. It's best to
>> make a clean copy and then work with that. Sometimes that means using
>> programs that are not FFmpeg.
>
> Thanks for that info about ffmpeg cleaning up.
>
> I had a look several months ago and also thought that ffmpeg could not really
> clean
> crusty sources.
>
> I had an impression that ffmpeg could only ignore some bad stuff and thus
> introduce gaps (lost frames, lost audio) and loss of lip sync. The doco
> seemed
> to me to be a bit light on for examples of dealing with the range of bad
> source
> video issues and the relevant options seemed hard-to-find, at least for me,
> since IIRC there were a few.
>
> I currently continue to use a now-defunct product "VideoReDo" which
> has a feature called QuickStreamFix which recognises and deals with those
> things
> (as well as removing audio delay) and maintains lip sync.
> VideoReDo was paid-for but FANTASTIC (the owner died and his wife won’t sell
> the IP,
> which is why the product is defunct) but it still works EXTREMELY well for
> the time being.
>
> I wish ffmpeg would consider putting a project together to be able to fix bad
> sources
> at least as well as VRD's QSF does, it'd be a great boon to the entire world 😊
>
> I also had a look around and found there's nothing on the planet (close to
> free) which
> does things as well, and saw some which purported to but did not (especially
> in a
> non-interactive "batch mode", ie a scheduled task, since they relied on a gui
> interface).
>
> If you have examples of ffmpeg doing such things then I would very much
> appreciate the information you have.
Okay, here's some.
setpts, like adding °F and °C
-----------------------------
You know of the
setpts=PTS-STARTPTS
filter, right? It sets the starting PTS to zero and it works very well.
How about
setpts=PTS-<number>?
Well, PTS is in ticks, ticks of the timebase clock. So, you'd expect
setpts=PTS-<ticks>
would be correct, right? For example, to cut 24/1.001 FPS video at frame
100,
setpts=PTS-375375.
Nooooooo! That's wrong. It should be
setpts=PTS-100.
So the setpts filter appears to add ticks and frames. That's like adding
°F and °C, which produces nonsense of course.
setpts=PTS-<number>
is not documented. It's the key to making frame-accurate cuts via FFmpeg
and it's not documented at all. Setting <number> to anything other than
<frames> and x264 gives you video with negative PTSes, non-monotonic DTS
errors and worse.
The same holds true for asetpts, except that PTS for audio is actually
SR (sample rate), usually 48000 samples/s. The documentation combines
setpts and asetpts and uses "PTS" for both. Oh dear.
What about when a video has studio splash screens at 30i that precede a
24i (i.e. soft telecine) movie?
Now, don't think too hard about this. You'll get brain damage.
Full Disclosure: I have not fully figured out asetpts yet, so I'm still
getting audio sync problems when I cut. But they're pretty quick and
easy to fix once I have transcoded video in hand.
If you'd like to work together, hydra3333, I'm keen.
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