[Ffmpeg-devel] issues transcoding 16:9 quicktime movies

[Phil C]

i posted this to the user list a couple of days ago.
but i would love to hear some of the developer's
comments on this issue i noticed.

i am trying to trans-code a quicktime movie which has
an aspect ratio of 16/9 into a mpeg2 video with the
same ratio. the problem is that ffmpeg is not
maintaining the aspect ratio or failing to set the
meta data as such. I'm using the current
cvs(Feb.11.2006) version of  ffmpeg .

I've attached a link to the sample file that I've been
using to test with. i know i can pass in the "-aspect
16:9" flag. when i do it sets the correct meta data as
witnessed by mediainfo
(http://sourceforge.net/projects/mediainfo) and plays
as i would accept. As far as i can tell ffmpeg seems
to be trans-coding correctly but it fails to set the
meta data. I'm not sure what to do because I'm not
sure if this considered a bug or a lack of features.
thanks in advance for spending your time looking into
this

http://home.comcast.net/~ffmpeg.files/sample.16.9.zip

-Phil

> Date: Sun, 12 Feb 2006 19:01:31 -0800 (PST)
> From: Alex Shaykevich <ashayk1 at yahoo.com>
>  Does it also do this when you set the output size
explicitly, ie. -s 
>720x480? 
>  --Alex

Yes 
-Phil

Date: Mon, 13 Feb 2006 09:58:40 +0100
From: "herve.flores" <herve.flores at free.fr>

> "-aspect" is just a bit of information in the mpeg
for display
> the resulting size will always be 720*480 (dvd
compliant)
> there is some other dvd compliant size of picture
but you don't mind
> The display on TV is OK (conservation of the aspect
ratio)

> with your source and your command I obtains :
>    Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p,
720x480, 29.97  
> fps, 9000 kb/s

> more informations:

>   Horizontal Size : 		720
>   Vertical   Size : 		480
>   Aspect          : 		4/3
>   FrameRate       :		 29.970030
>   BitRate         : 		9000
>   Format : 			MPeg2
>   Progressive : 		Yes
>   Format Chroma : 	4:2:0
>   Begin Time : 		00:00:00.00
>   End Time   : 			00:00:23.11
>   Duration   : 			00:00:23.11

> then use:
> ffmpeg - i <input> -target ntsc-dvd -aspect 16:9
<output>
> 
> if you want to add black lines, use the padtop and
padbottom (you can  
> automatise it with a "GUI")
> - first read the verbose with ffmpeg -i <input>
> - collect the verbose and determine the black lines
you need
> - send the good parameters
> 
> it's not a bug, ffmpeg just  encode what you said it
to encode, if  
> you want something different (like to conserve
ratio, use parameters)
> A lot of sources are really bad encoded (metadata or
even ratio is  
> false!)
> with the non-automatically perservation of ratio you
manage to do  
> more...
> (sorry for the very bad formulation ;-))


here is the issue as far as i know, mpeg2 uses the
same resolution (720x480 for ntsc) for both 4:3 and
16:9 aspect ratios. using the aspect meta data to
determine how to play the file.  so i think it should
be considered a bug, so that being said i would like
to know the reasoning behind it not being considered a
bug. and i know i can reslove the issue by passing in
the "-aspect 16:9" flag to ffmpeg but considering how
i think mpeg2 works. that shouldnt be necessary.


-Phil


> bye

> Herv?


ffmpeg.exe -i Pompeii_16x9.mov -target ntsc-dvd
test1.mpg
FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice
Bellard
  configuration:  --enable-mp3lame --enable-mingw32
--enable-a52 --enable-gpl --enable-memalign-hack
--enable-pp --extra-cflags=-I/local/include
--extra-ldflags=-L/local/lib
  libavutil version: 49.0.0
  libavcodec version: 51.2.0
  libavformat version: 50.2.1
  built on Feb 11 2006 16:40:06, gcc: 3.4.2
(mingw-special)

Seems that stream 0 comes from film source: 600.00
(600/1) -> 20.00 (20/1)
Input #0, mov,mp4,m4a,3gp,3g2, from
'Pompeii_16x9.mov':
  Duration: 00:00:23.3, start: 0.000000, bitrate: 1576
kb/s
  Stream #0.0(eng), 20.00 fps(r): Video: svq3,
yuv420p, 852x480
Output #0, dvd, to 'test1.mpg':
  Stream #0.0, 29.97 fps(c): Video: mpeg2video,
yuv420p, 720x480, q=2-31, 6000 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
frame=  701 q=2.0 Lsize=    8212kB time=23.4
bitrate=2880.2kbits/s
video:5459kB audio:0kB global headers:0kB muxing
overhead 50.441866%

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