av_find_stream_info failed for any but first file
Probably an ffmpeg bug.
When trying to read more than one file with ffmpeg (or also the same file multiple times), only the first performance works. Any further attempt to read a file yields:
[00000421] ffmpeg demuxer debug: detected format: mp3
[00000421] ffmpeg demuxer error: av_find_stream_info failed
and VLC falls back to PS demux (which of course fails).