[FFmpeg-user] Aspect ratio preservation in WMV

[Mark Richards]

The problem is that ffmpeg has defaults for ratios, dimensions, bitrates,
etc..., and I am guessing ratio is one of them.  You probably need to
specify those values yourself when you transcode, to ensure you preserve the
dimensions, bitrate, etc...  Some of the values of "copy" options.
Unfortunately, you'll have to scour the documentation.  I'd gladly tell you
them if I knew, but I haven't needed to "copy" values myself.

Mark

-----Original Message-----
From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-bounces at ffmpeg.org]
On Behalf Of Paul-Antoine Arras
Sent: Monday, September 26, 2011 1:14 PM
To: FFmpeg user questions and RTFMs
Subject: Re: [FFmpeg-user] Aspect ratio preservation in WMV

Le 26/09/2011 01:23, Rodney Baker a écrit :
> On Mon, 26 Sep 2011 02:18:34 Paul-Antoine Arras wrote:
>> Le 24/09/2011 04:17, Rodney Baker a écrit :
>>> On Sat, 24 Sep 2011 04:50:52 Paul-Antoine Arras wrote:
>>>> Hello,
>>>>
>>>> I'm trying to convert the sound of a video from WMA to MP3. To do 
>>>> so, I
>>>>
>>>> use the following command line:
>>>>       ffmpeg -i input.wmv -acodec libmp3lame -aq 4 -vcodec copy
>>>>       output.wmv
>>>>
>>>> The sound is converted correctly but the aspect ratio (AR) becomes 
>>>> 4:3
>>>>
>>>> instead of 16:9. Then I've tried to force the AR with:
>>>>       -aspect 16:9
>>>>
>>>> without success.
>>>>
>>>> Why does ffmpeg modify the AR while all it has to do in this case 
>>>> is a simple copy of the video part? How to make it preserve the 
>>>> original AR (16:9)?
>>>>
>>>> Thanks in advance for your help.
>>>
>>> You need to provide the full output from ffmpeg.
>>
>> Here is the full output from ffmpeg:
>>
>> FFmpeg version 0.6.2-4:0.6.2-1ubuntu1.1, Copyright (c) 2000-2010 the 
>> Libav developers
> [...]
>> Output #0, asf, to 'output.wmv':
>>     Metadata:
>>       WM/EncodingSettings: Lavf52.64.2
>>       Stream #0.0: Video: WMV3 / 0x33564D57, yuv420p, 720x576 [PAR 
>> 64:45 DAR 16:9], q=2-31, 1k tbn, 1k tbc
> ^^^^^^^^^^^^
>
> ffmpeg is writing the stream out with an aspect ratio of 16:9 (Display 
> Aspect
> Ratio) and pixel aspect ratio of 64:45 which, with a standard 
> definition
> 720x576 picture will be correct for a 16:9 display. What are you using 
> to view the resultant output file? Is it showing the correct aspect 
> ratio?  Can you force it?
---
When I open output.wmv with VLC, the video is displayed as 4:3, then I can
force it to 16:9 by software. But the purpose of what I'm trying to do is
making the video readable on my set-top box, which renders it as
4:3 (just like VLC) and can't be forced to another ratio.
--
Paul-Antoine ARRAS
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