fastest way to encode imageSequence to avi

[yair]

hi,
i'm figuring out a 3d vision workflow which calls for taking two image seq and horizontally stacking them.
i'm using corona imageSequence plugin as i find it can handle more filetypes then imageReader, and i have this script.

clip1 = CoronaSequence("C:\Users\yair\Desktop\avs23d\demo2\leftCam_%.4d.png", sort=1, start=0, stop=401)
clip2 = CoronaSequence("C:\Users\yair\Desktop\avs23d\demo2\rightCam_%.4d.png", sort=1, start=0, stop=401)
StackHorizontal(clip1 , clip2)

problem is in 2k res this thing crawls to a stutter. but if i "bake" it to video it runs ok.
so i am experimenting with all sorts of encoders to make it as fast as i can, for preview. (the final result will be encoded to digital cinema spec ,currently i haven't gotten there).

this works,

ffmpeg -i input%05d.png -vcodec mjpeg -qscale 1 output.avi


but im looking for a faster route. maybe rawvideo, which i couldn't get to work
.

ffmpeg -i input%05d.png -an -vcodec rawvideo output.avi


as no compression is involved i expect this to be the fastest way, but i cant get it to work. i get

Input #0, avs, from 'C:\Users\yair\Desktop\avs23d\avs\leftCam_Right_sideBySide[0-401].avs':
Duration: 00:00:16.08, start: 0.000000, bitrate: 0 kb/s
Stream #0.0: Video: rawvideo, bgra, 1280x480, 491520 kb/s, 25 tbr, 25 tbn, 25 tbc
[avi @ 016980c0]Tag 0x41524742 incompatible with output codec
Output #0, avi, to 'out.avi':
Stream #0.0: Video: rawvideo, bgra, 1280x480, q=2-31, 200 kb/s, 90k tbn, 25 tbc
Stream mapping:
Stream #0.0 -> #0.0
Could not write header for output file #0 (incorrect codec parameters ?)


if this is more relevant to another section, please fwd.