[mythtv-users] Transcoding and aspect ratio (DVB-T)

[Ian Grant]

Ian Grant wrote:
> --On 28 February 2006 2:02 PM -0500 Chris Pinkham <cpinkham at bc2va.org> 
> wrote:
>
>   
>> I received your files and they have the correct aspect in them, they have
>> an aspect of 2, so I assume that is still your modified code that passes
>> 2.0 to SetVideoAspect. What does your nuvinfo say about the
>> transcoded.nuv file you emailed me?  Here's the output from mine:
>>
>> P</tmp/ctp> nuvinfo transcoded.nuv | more
>>
>> info for: transcoded.nuv
>>
>>                  aspect:  2
>>   audio_bits_per_sample:  16
>>
>>
>> --
>> Chris
>>
>>     
>
> First, thanks for looking at them.
>
> That is.. bizarre -- here is my output:
>
> info for: transcoded.nuv
>
>                  aspect:  4:3
>                aspect_f:  1.33333333333333
>   audio_bits_per_sample:  16
>
> info for: original.nuv
>
>                  aspect:  16:9
>                aspect_f:  1.77777777777778
>           audio_bitrate:  256000
>   audio_bits_per_sample:  16
>
> How can that be? You're right, they are transcoded with 
> SetVideoAspect(2.000).
>
>
> Ian.
>
>   

Okay, so I found the following code in nuvinfo:

             # Make some corrections for myth bugs
156             $info{'audio_sample_rate'} = 44100 if
($info{'audio_sample_rate'} == 42501 || $info{'audio_sample_rate'} =~
/^44\d\d\d$/);
157             $info{'aspect'} = '4:3';

This appears to return 4:3 for nuv files regardless of what is in the
file?! I commented out line 157 there and I now get the correct aspect
ratio reported by nuvinfo, which is as you experienced above.
Unfortunately they still play as 4:3 in VLC/MPC, so I must assume that
the error is in the detection with the player.

On a side note, it appears nuvinfo uses 'mplayer -identify' to get the
aspect ratio for mpg files (or nuvs which are really mpeg).
When I do mplayer -identify on a transcoded nuv file, it reports
'ID_VIDEO_ASPECT=0.0000'

Here's what I think: mythtranscode writes the aspect ratio into the nuv
container, but not into the MPEG4 stream that is inside. MPEG2 mpg files
do contain this aspect ratio in the file.
VLC/MPC client is unable to get the aspect ratio out of the nuv
container, and so attempts to use the aspect ratio in the video stream,
which works for MPEG2, but not transcoded MPEG4 streams.
Probably a 'normal' Myth frontend doesn't experience this problem
because it can properly read the nuv container. Unfortunately I don't
have a proper frontend.
What does anyone think? Am I wrong..?


Ian.


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