[MPlayer-users] Mencoder: Changing frame rate (RealMedia to vcd)

[Giacomo Comes]

On Sat, Jan 01, 2005 at 12:23:44PM -0800, Bill Moseley wrote:
> On Sat, Jan 01, 2005 at 03:35:09PM -0400, Giacomo Comes wrote:
> > In general going from resolution A aspect B to resolution C aspect D
> > requires expand and scale or scale and expand.
> 
> Why does it make a difference (other than a bug in some software)?

The only difference is in the numbers.

Example: video 576x288 aspect 2:1 to convert to 16/9 720x480 (NTSC DVD)
with expand and scale you need:
	-vf expand 576:324,scale=720:480
with scale and expand you need:
	-vf scale=720:426,expand=720:480

The final result is exactly the same (other than bug).

> 
> My basic understanding is you can pick 16:9 or 4:3 so you have to
> expand, that is, convert the current image to one of those ratios by
> either adding black bars (to keep all the image) or by
> trimming/cropping.  Then it needs to be resized to fit the target
> format (i.e. 720x480 for dvd).  And then there has to be a flag to
> tell the player if it's 16:9 or 4:3.
> 
> [What happens after to get the image is shown on my direct view
> 16:9 TV is a mystery to me.]
> 
> 
> > By the way encode2mpeg deals with all these situations. The option
> > -mpegfixaspect is your friend.
> 
> Yes, very cool.  I've been playing with this sample:
> 
>    http://service.real.com/learnnav/testrams/realvideo10_512.ram
> 
> And using this command line:
> 
>    encode2mpeg -o STEST -n p -mpegfixaspect pad -imageonly -mpeg -svcd sample.rm
> 
> I get a lot of "[mpeg2video @ 0x403b9008]rc buffer underflow" and
> other messages.  I'm not sure if that indicates a problem or not.

Most of the time no. The current
mpeg muxer in mencoder produce them and it's not possible to avoid them.

> 
> And I have not figured out how to make the resulting mpeg flagged as
> 16:9 content.  I've tried this:
> 
>   encode2mpeg -o STEST16 -a 3 -n p -mpegfixaspect pad -imageonly -svcd -mpeg sample.rm

the command is correct. -a 3 set 16/9 aspect.

> 
> BTW -- you recommended 
> 
>   encode2mpeg -o MYREAL -n n input.rm -encode 2
> 
> doesn't that make a divx intermediate file?  It's that a lossy
> operation to go from Real -> divx-> mpeg1/2?

Yes it's lossy, but I'm sure you will not notice any difference.
-encode 2 keep the quality good in the avi. But in case there is
a visible loss in the quality you can use -encode 4.
I recomended the previous line (Indirect Mode) because I'm still
trimmering the libavcodec options of Mpeg Mode.
I'm almost done and in next relase Mpeg Mode will be "well defined".

Giacomo
> 
> Thanks very much -- the encode2mpeg is a huge help.
>