Usually we use the MJPEG streaming function of the Broadcaster (why?), which can be accessed through http://10.73.x.2:1881/vgabroadcaster.mjpg on older generation models, and through http://10.73.x.2:1881/stream.mjpg on new gen models (called VGADVI Broadcaster).

Assuming a 16:9 projector, use the following line to feed the mjpeg stream to DVSwitch:

ffmpeg -i http://10.73.x.2:1881/vgabroadcaster.mjpg \
  -target pal-dv -loglevel error -aspect 16:9 - | \
  dvsource-file-voc -h "10.73.x.1" -i 1 -p 2000 /dev/stdin

This fetches the image off the framegraber and distorts it to fill the video image. If the projector requires a 4:3 resolution, uou first need to upload an EDID file to the broadcaster (see respective section). Next, you need to add artifical bars on the left and on the right by replacing above line in /etc/services/grabbersource by this (or by modfiying it accordingly):

ffmpeg -i http://10.73.x.2:1881/vgabroadcaster.mjpg \ 
  -filter:v 'scale=768:576, pad=1024:576:128:0 , scale=720:576' \
  -target pal-dv -loglevel error -aspect 16:9 - | \ 
dvsource-file-voc -h "10.73.x.1" -i 1 -p 2000 /dev/stdin

A final problem that you might be facing is a presenter with 16:9 slides. The computer of the speaker will add black rows on top and bottom to accomodate for the 4:3 aspect. In total, this will now have borders on all four sides and make the slides appear much smaller than necessary.

The recommendd workaround is to add a second source that cuts off the black bars received from the laptop. Run the following line inside a screen session on one of the encoders:

ffmpeg -i http://10.73.x.2:1881/vgabroadcaster.mjpg \ 
  -filter:v 'crop=h=3/4*in_h, scale=720:576' \
  -target pal-dv -loglevel error -aspect 16:9 - | \
dvsource-file-voc -h "10.73.x.1" -i 5 -p 2000 /dev/stdin

MJPEG with “Default” setting (not “High speed”) 25 fps no audio no recording

broadcaster lite partition layout

Disk /dev/sdc: 1967 MB, 1967128576 bytes
61 heads, 62 sectors/track, 1015 cylinders, total 3842048 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1   *           1     1051395      525697+   b  W95 FAT32
/dev/sdc2   *     1051396     3838729     1393667   83  Linux