Could not find codec parameters -- for gif? The scene: Ubuntu 16.04, newly upgraded from 14.04 where things perked along happily with avconv

The props: a directory full of stills, motor_animate_000.gif, motor_animate_001.gif, etc.

The players: Me, a mostly-newbie ffmpeg user, and ffmpeg.

The drama:

Based on a suggestion I had to solve another problem, I execute the command line:

ffmpeg -f image2 -framerate 30 -i motor_animate_%03d.gif motor.mpg

After the usual excrutiating detailed list of stuff from ffmpeg, I get the following error message (in more than one color, ooh, ooh).

[image2 @ 0x14f8420] Could not find codec parameters for stream 0 (Video: none, none): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' options
motor_animate_%03d.gif: could not find codec parameters
Input #0, image2, from 'motor_animate_%03d.gif':
  Duration: 00:00:04.03, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: none, none, 30 fps, 30 tbr, 30 tbn, 30 tbc
File 'motor.mpg' already exists. Overwrite ? [y/N] y
No decoder for stream #0:0, filtering impossible
Error opening filters!

Can anyone tell me what's going on and how to fix it?  All I want to do is make an mpeg clip out of a bunch of one-frame gifs.

Thanks.
It's worth a try using the concat demuxer.

First, create a text file like this:

file 'motor_animate_000.gif'
file 'motor_animate_001.gif'
file 'motor_animate_002.gif'
file 'motor_animate_003.gif'
...


Then run

ffmpeg -f concat -i list.txt motor.mpg


Do note that by just specifying a .MPG filename as output parameter, ffmpeg will encode to MPEG-1 at a bitrate of 200 kb/s. If MP4 is not acceptable and .mpg is needed, then add -c:v mpeg2video -b:v 1000k after list.txt to set codec and avg. bitrate. For MP4, just change extension; the defaults are decent.