[FFmpeg-user] Video scaling, padding and cropping together question

[TPCffmpeg at mklab.ph.rhul.ac.uk]

I am attempting to down-convert HD video (1280x720 with 16:9 aspect ratio) 
to 720x576 for use on an old PAL 4x3 display.  I found two days of doing 
this, using,

(1) -filter:v scale=iw*min(720/iw\,576/ih):ih*min(720/iw\,576/ih), pad=720:576:(720-iw*min(720/iw\,576/ih))/2:(576-ih*min(720/iw\,576/ih))/2 -target pal-dvd
(2) -filter:v 'crop=ih/3*4:ih' -target pal-dvd

Method 1 scales and pads to letterbox format, so I get the whole of the 
original picture width with bars above and below.  Method 2 scales and 
crops, so I get to use the whole 4x3 display screen height (better 
resolution) but lose the LH & RH picture edges via the cropping.

The thing I am trying to achieve is a compromise between these two 
extremes, eg. a method which gives less cropping at the LH & RH picture 
edges for the price of a little padding above and below the picture.  I'm 
presuming this (ideally) involves scaling, padding and cropping together 
in a single filter.

Could anyone show how to do this or point me in the right direction?

Many thanks
Tom Crane

-- 
Tom Crane, Dept. Physics, Royal Holloway, University of London, Egham Hill,
Egham, Surrey, TW20 0EX, England.
Email:  T.Crane at rhul.ac.uk
Fax:    +44 (0) 1784 472794