[FFmpeg-user] Changing DAR ?

[Ronald F. Guilmette]

In message <loom.20131009T001211-883 at post.gmane.org>, 
Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

>Ronald F. Guilmette <rfg <at> tristatelogic.com> writes:
>
>> ffmpeg -i foo.avi -acodec copy -vcodec copy -vf setdar=16/9 bar.avi
>
>This cannot work: Video filters ("vf") don't work with 
>-vcodec copy.

Ahhhhhhh!!  That is quite obviously the epiphany I was looking for,
even without knowing it.  Thank you!  That would explain some things.

>Sorry if I was unclear before:

You are e gentleman, and greatly respect and appreciate that.  However
_you_ certainly have nothing to apologize for.  I'm not sure that I can
say the same for ffmpeg itself however.

If what you say is true... and I have no reason whatever to disbelieve your
assertion... then ffmpeg, being a reasonable and otherwise well-behaved
program, conforming to common, pre-existing and long-standing general
rules of polite program behaviorial etiquette, should produce a fatal
error and refuse to do anything at all when it is invoked with a clearly
erroneous command line like the following, wouldn't you agree?

 ffmpeg -i input.mp4 -acodec copy -vcodec copy -vf setsar=sar=16/9 output.mp4

Strangely however, it does not do so.  Instead, it proceeds and generates
an output file, even while giving -no- helpful hint whatsoever to the user,
either in the form of an error or even a warning message, that he's done
anything wrong at all.

So, you know, I am ernestly puzzled.  How can this be, if what you said
about is actually true (and as I've already said, I _do_ believe you,
in no small part because what you said makes perfect sense).

>I suspect that what you 
>want is possible with FFmpeg but if you cannot provide 
>both the command line you tried and the console output, 
>at least I am unable to help you.

Actually, you already _have_ helped me a great deal, just by informing
me that the "-acodec copy" option is fundamentally incompatible with
the -vf option... a rather important fact which I ernestly did not know
_and_ which, more importantly, ffmpeg did not have the simple courtesy
to inform me about... you know... before you did.

I'm going to go back now and try playing with some of my video files
to see what other useful bits of enlightenment I can come up with on my
own, but I am likely to have more questions later on.

For now, if you have the time, I'd just like to know what ffmpeg can
and cannot do with respect to modifications to aspect ratio (either
DAR or PAR or SAR) *without* full-scale re-encoding and for each of
the following:

	MPEG-4/10
	MPEG-4/2
	WMV9
	WMV8
	WMV7
	MPEG-2
	... and anything else you happen to know about...


Thanks!