Output format for a still image from avconv -

i'd generate still image video in mpeg pipe, like

avconv -ss 0:01 -i my.mpg -frames:v 1 -f jpeg - 

however, avconv (ffmpeg) not have jpeg among allowed output formats. there no problem specify format output extension:

avconv -ss 0:01 -i my.mpg -frames:v 1 my.jpg; cat my.jpg 

but don't want create redundant files. hint?

from docs, can pipe stdout setting output filename pipe protocol, i.e. pipe:1. , though it's not stated explicitly, can set output format file extension, same way normal filename:

avconv -ss 0:01 -i my.mpg -frames:v 1 pipe:1.jpg 

sidenote:

note formats (typically mov), require output protocol seekable, fail pipe output protocol