[FFmpeg-user] I found the bugs

[Paul B Mahol]

On Mon, Jun 17, 2024 at 5:35 PM Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 17/06/2024 03.16, Paul B Mahol wrote:
> > On Mon, Jun 17, 2024 at 3:16 AM Mark Filipak <markfilipak.imdb at gmail.com
> >
> > wrote:
> >
> >> To expand on my idea:
> >>
> >> The video is this:
> >> I P B B P B B P B B I P B B..
> >> I want to change it to this:
> >> I B B P B B P B B P I B B P..
> >>
> >
> > If this is what I think it is, your are wasting your time.
>
> It is possible. But can FFmpeg do it? You see, Paul, I read in several
> places from seemingly
> authoritative people that professional videos are PTS-ordered. I've since
> discovered that
> professional videos are almost always DTS-ordered -- I now have a packet
> browser and have seen it to
> be true. However, I have seen professional videos that are PTS-ordered but
> I didn't think too much
> about it at the time.
>

PTS order is order once frames are decoded and going to be presented to
user, thats why it is called presentation timestamps.


>
> My idea is to take the 4-second video -- DTS-ordered -- that I sent to
> trac, change it to
> PTS-ordered, and see if '-vf showinfo' and '-f show_frames' respond
> correctly. It's a long shot, but
> it might show something useful -- what if PTS-order made showinfo
> show_frames and framecrc all
> agree? Wouldn't that be something interesting?
>

If decoder follows specifications for decoding bitstreams correctly than
changing order of raw encoded frames as stored in bitstream will almost
every-time cause broken decoding.


>
> > Its nonsense to change order of encoded frames, no manipulation of clock
> > can fix that.
>
> No, no. Manipulation of PCR. Fix up the PCRs so that the result is truly
> PTS-ordered.
>

If this is at format container layer, I dunno how would that work even if
its is possible to be useful.



>
> > When doing concat you can not concat in middle of group of frames.
>
> I'm not doing that.
>
> > Each beginning and end frame must be the key-frame.
>
> Of course.
>
> >> To do that, I reckon I need to,
> >> 1, move the packets that contain P-frames,
> >> 2, insert revised 'program_clock_reference_base's and
> >> 'program_clock_reference_extension's into each
> >> of them to account for the new order, and
> >> 3, do some packet fixup (maybe).
> >>
> >> Is that possible with FFmpeg?
> >>
> >> --Mark.
>
>
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