Top Node AutoWrite

if you need your output file named exactly like your input file then use a little TCL expression in the file knob of the write node

suggestion your filename convention is like: //path/to/file/filename.pattern.ext

then:

[lindex [split [lindex [split [knob [topnode].file] .] 0] /] end]

will give you back just the "filename" part of the original read node

if you want to write to same folder as the original file but with a new filename extension you could use:

[file dirname [knob [topnode].file]]/[lindex [split [lindex [split [knob [topnode].file] .] 0] /] end]_conv.%04d.exr