[FFmpeg-user] Changing DAR ?

[Ronald F. Guilmette]

I am trying to use ffmpeg (2.0.1) to make what I believe should be
a simple change in a video file I have, and it's just not happening,
so I need to ask what I am doing wrong.  (Please note that I am laboring
under the disadvantage of substantial ignorance about a lot of this stuff,
so please bear with me and be kind.)

Basically, the file I have, when played on various players, just looks
wrong, i.e. a big stretched horizontally.  I've run mediainfo on the
file and the output of that is attached below.

I cannot help but notice that in this output, the display aspect ratio
is set to a rather strange value, i.e. 2.011.  I do suspect that the
proper value should be 16:9 (1.7777).  Anyway, I would like to try
setting it to 16:9 and then see if the video looks reasonably normal
after that.  (I confess that I don't even have any idea as to whether
that 2.011 value that mediainfo is reporting is relevant to the container
or to the video stream, so any enlightenment on that point would be
appreciated too.)

Of course, if I can avoid wholesale re-encoding while ``fixing'' the
DAR, then I'd like to do that.

So anyway, I've tried ffmpeg (2.0.1) with the "-acodec copy" and
"-vcodec copy" options and using those, I have run two different
experiments.  In the first, I added "-aspect 16:9" and that had no
apparent effect at all.  In the second I tried instead adding
-vf setdar=16:9 (although this appears to be a magic undocumented
thing that, although mentioned in various online posts is most
definitely _not_ documented in the ffmpeg online documentation at
all).  Anyway, that also had no apparent effect.  In both cases,
running mediainfo on the resulting output files shows the DAR
_still_ set to the value 2.011, which is not at all what I want.

And help or advice would be appreciated.


Regards,
rfg


P.S.  I am beginning to think that what the world really needs, in addition
to a good 5 cent cigar, is a nice tutotial page someplace that would go
into some depth explaining all of the ins and outs of DAR, PAR, and SAR,
and which would also clarify not only how to simply _find_ those values
for any given video (in any given popular format), _both_ as they may be
encoded in the video stream _and_ also in the container(s), for various
popular container formats, but also and further, how to _modify_ each of
those independent aspect ratios, using ffmpeg and other tools, e.g
WINARChanger, Yamb, etc., again both on the container level and on the
stream level.  After some searching, I have found that this information
is hard to come by on the web, and when one does find some info on this
topic, it is fragmentary and almost always unenligntening.  (For example,
I've seen where several people suggest using YAMB to change DAR.  OK, so
I downloaded the thing and installed on omy Win7 system, and managed to
get it to open the file of interest.  Swell.  NOW WHAT?  If there is a
way to get this thing to change the DAR I sure as hell don't see it.
Whatever it is, if it is there, it is non-intutive and non-obvious.
Sigh.  That's OK, I guess.  I would prefer to be using ffmpeg from the
command line over on my FreeBSD system anyway.)

Anyway, maybe I myself might take a stab at writing up a web page like
what I have suggested just above... the "Video Aspect Ratios for Dummies".
I would probably be the perfect guy to write this, since I *am* a dummy,
and so I'd be starting almost from scratch, and (thus) I'd have to
go 'round and badger all sorts of experts to gather all the info for
the page, and I would not be polluted by any pre-established under-
standings of this stuff, since I have (essentially) none.

mediainfo output:
============================================================================
General
Complete name                            : Kr.avi
Format                                   : AVI
Format/Info                              : Audio Video Interleave
File size                                : 105 MiB
Duration                                 : 5mn 14s
Overall bit rate                         : 2 797 Kbps
Writing library                          : VirtualDub build 32817/release

Video
ID                                       : 0
Format                                   : MPEG-4 Visual
Format profile                           : Advanced Simple at L5
Format settings, BVOP                    : 1
Format settings, QPel                    : No
Format settings, GMC                     : No warppoints
Format settings, Matrix                  : Default (MPEG)
Codec ID                                 : XVID
Codec ID/Hint                            : XviD
Duration                                 : 5mn 14s
Bit rate                                 : 2 593 Kbps
Width                                    : 720 pixels
Height                                   : 358 pixels
Display aspect ratio                     : 2.011
Frame rate                               : 29.970 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Compression mode                         : Lossy
Bits/(Pixel*Frame)                       : 0.336
Stream size                              : 97.2 MiB (93%)
Writing library                          : XviD 64

Audio
ID                                       : 1
Format                                   : AC-3
Format/Info                              : Audio Coding 3
Mode extension                           : CM (complete main)
Codec ID                                 : 2000
Duration                                 : 5mn 14s
Bit rate mode                            : Constant
Bit rate                                 : 192 Kbps
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 KHz
Bit depth                                : 16 bits
Compression mode                         : Lossy
Stream size                              : 7.20 MiB (7%)
Alignment                                : Aligned on interleaves
Interleave, duration                     : 33 ms (1.00 video frame)
Interleave, preload duration             : 512 ms