Concatenating video files with ffmpeg, no sound in output file

Concatenating video files with ffmpeg, no sound in output file

I am concatenating different AVI video files.
ffmpeg -f concat -i inputs.txt -c copy output.avi
The input files has been specified in input.txt in the order required.
First video file does not have sound track, but subsequent files have.
After completion the resulting the operation, the output does not have audio!
If I remove first video files from input then resulting video gets sound.
So it means the output format follows the first item in input list. How
can I solve this problem.
Please suggest the options in ffmpeg or avconv not in any other tools like
mencoder.
Thank you