[FFmpeg-user] I found the bugs

[Paul B Mahol]

On Mon, Jun 17, 2024 at 8:29 PM Mark Filipak <markfilipak.imdb at gmail.com>
wrote:

> On 17/06/2024 13.50, Paul B Mahol wrote:
> > 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.
>
> Yes of course.
>
> >> 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.
>
> The container would contain a PES packet stream with PCRs like any other
> PES packet stream. It would
> work like any PTS-ordered stream does. You know, there _are_ PTS-ordered
> streams. And you know, MPEG
> is silent on the matter of what physical order frames are in the stream,
> only that they must be
> given to the decoder in DTS-order.
>
> Look, I agree that it would be nonsense. I want to turn the DTS-ordered
> stream into a PTS-ordered
> stream merely as a test: '-f show_frames' appears to be getting DTSes and
> PTSes mixed up, then
> applying a fix that results in completely new DTSes. If it treats the
> PTS-ordered stream
> differently, that will say a lot. What is says depends on what it does.
> Capiche?
>
> I thought I could do it by demuxing, then moving them like you can move
> frames in a filter_complex,
> and then remuxing, but I don't know how to do that to PES packets (instead
> of decoded pictures) and
> I don't know how to rewrite PCRs.
>

But aren't you working with HEVC and not MPEG video?


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