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

Ian Grant mailinglists at iangrant.me.uk
Fri Mar 31 09:15:38 UTC 2006


I posted a message on the DSMyth forum at SourceForge 

'I'm having problems with detection of the aspect ratio when playing nuv 
files through dsmyth.
This thread documents my efforts so far to unearth the problem: 

The problem is that MPEG2 TS .mpg recordings play fine, but after 
transcoding, the resulting MPEG4
.nuv file always appears as 4:3, I have to manually force VLC or MPC to 
16:9 mode.
I'm wondering if dsymth is not able to detect the aspect ratio in the .nuv 

I think that the aspect ratio is in the MPEG2 stream for .mpg files, and 
the MPEG2 decoder picks it up fine, but I *believe* that the transcoded 
MPEG4 file does not have the aspect ratio in the MPEG4 stream, but rather 
in the .nuv container.

Does anyone know any different, or have any ideas, etc.?'

Eventually, I got a reply:

'the problem with the nuv format is that there is no way to properly 
specify the aspect ratio.
remember that the aspect can change in a recording (commercial break, 
start/end of show and so on)

there is one field in the nuv file header for aspect ratio, but this is 
always set to 4:3 by mythtv.

what you can do is to specify a resolution that is 16:9 when you transcode 
it, or if it's possibel to convince mythtvs transcoder to add black bars to 
the transcoded file.
but i haven't tried this myself since i don't transcode my recordings.'

So, it seems the ideal solution would be to have mythtranscode write the 
aspect ratio into the MPEG4 stream, as per the original MPEG2 file (I 
assume it's written per-frame, or something).
Does anyone know if this is possible, or if the Myth developers are even 
aware of this?


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