Is not that the error because error go out if you add - or not:
> cat CD1.avi CD2.avi | ffmpeg -i -acodec copy -vcodec copy Agora.2009.DVDRip.2.avi
ffmpeg: relocation error: ffmpeg: symbol av_destruct_packet, version LIBAVFORMAT_52 not defined in file libavformat.so.52 with link time reference
> cat CD1.avi CD2.avi | ffmpeg -i - -acodec copy -vcodec copy Agora.2009.DVDRip.2.avi
ffmpeg: relocation error: ffmpeg: symbol av_destruct_packet, version LIBAVFORMAT_52 not defined in file libavformat.so.52 with link time reference
Is not that the error because error go out if you add - or not:
> cat CD1.avi CD2.avi | ffmpeg -i -acodec copy -vcodec copy Agora.2009. DVDRip. 2.avi
ffmpeg: relocation error: ffmpeg: symbol av_destruct_packet, version LIBAVFORMAT_52 not defined in file libavformat.so.52 with link time reference
> cat CD1.avi CD2.avi | ffmpeg -i - -acodec copy -vcodec copy Agora.2009. DVDRip. 2.avi
ffmpeg: relocation error: ffmpeg: symbol av_destruct_packet, version LIBAVFORMAT_52 not defined in file libavformat.so.52 with link time reference