[FFmpeg-user] Changing DAR ?

[Ronald F. Guilmette]

In message <loom.20131010T022139-183 at post.gmane.org>, 
Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

>Ronald F. Guilmette <rfg <at> tristatelogic.com> writes:
>
>> I'm gonna have to grub around down in the code to find 
>> the various relevant header formats and fields
>
>This is possible and certainly not unwanted!
>
>(On the contrary.)

Yes.

The only problem is finding the time.  (It appears, just glancing at the
initial output of "make" that most or all of this stuff is in C, in which
I have excellent fluency, so like I say, it is only a question of finding
the time.)

>If you just to want to solve your problem, the alternative 
>is of course still to post the command line you tried 
>together with the complete, uncut console output.

Thank you, ernestly.

So far I have found workarounds for eveything I've wanted or needed to do,
with the help of some small Windoze utilities (specifically WMVARChanger
for modern WVM9 stuff, MPEG4Modifier for MPEG-4/2 stuff, and DVDPatcher
for MPEG2 stuff), and I seem to be able to use ffmpeg to diddle aspect
ratios to my liking when I use it on MPEG-4/10 stuff... as long as I'm
willing to repackage it into output .MKV files.  So I think I'm good
for now, but aas a general principal I _do_ like to understand anything
and everything that I ever mess with, so eventually I'll come back to
all this and try to get a better understanding of it all.

In an ideal world, there would be one siingle tool (to rule them all? :-)
which would be able to do everything that can be done, even theoretically,
as regards to changing aspect ratios on all these different formats, and
more, *without* full re-encoding, and perhaps someday I might even create
such a thing.  But alas, today is not that day.

(I gather that in most or all of the video stream formats there are one
or more fields in the headers that describe aspect ratio(s)... either
"storage" or "pixel" or "display" or all of the above, and that separately,
in certain formats at least, there may be separate fields which also try
to specify aspect ratios, but that these are embedded at various points
with the actual video stream itself.  It seems clear that those could be
diddled (programatically) too, without full re-encoding, but with the
exception of DVDPatcher, which is limited to only MPEG-2, I've yet to
find tools that do this for other formats, let alone generally, for all
formats, which would be most helpful.  Oh well.  Someday.)