ffmpeg concat: "Unsafe file name"

The answer stated by @Mulvya (thank you!) works: "Add -safe 0 before -i". Then another problem appeared with find STREAM -name '*' -printf "file '$PWD/%p'\n" which returns the empty path as first entry. Changed this for for f in ./*.wav; do echo "file '$PWD/$f'"; done (see https://trac.ffmpeg.org/wiki/Concatenate) and now it seems to work. Hurray!

In my case, double quotes causes the error.

I use ffmpeg -f concat -i concat.txt -c copy output.m4a command, which the concat.txt contains list of input file to concat.

Unsafe file name (double quotes treats as part of filename, -safe 0 can't fix this):

file "song1.m4a"
file "song2.m4a"

Safe file name (single quotes):

file 'song1.m4a'
file 'song2.m4a'

Safe file name (without quotes):

file song1.m4a
file song2.m4a

The above single quotes and without quotes only safe if it only contains "letters, digits, period(except prefix), underscore and hyphen". So the following common filename will not works:

• space
• glyph
• / (path)
• prefix period (hidden file)

You still need -safe 0 for that cases.

[Caveat about Quoting and escaping]

You always need escape ' in the part of filename. the reason is because of file Im' .avi will added closing quote automatically to Im' .avi', which is same as file Im' .avi'. The last odd quote in file Im' .avi'''''' also will added closing quotes become file Im' .avi''''''' , so it doesn't have No such file or directory error. I figure out this phenomena because of space no longer need to escape by \ after prefix with single quote, without have to add closing quote.

Despite of above(must escape ' by \ and not escape with "), the escape style is similar to shell. If filename contains single quotes, you can either escape it with I\'m\ .m4a(NOT surrounded with single quotes) style, or 'I'\''m .m4a' OR 'I'\''m'\ '.m4a'(surrounded with single quotes) style, but neither of 'I\'m\ .m4a' nor 'I'm .m4a'.

When you test ffmpeg, be aware of the first line error message Impossible to open may misleading(the file does exist), you need check the second line which is either of No such file or directory(file not exist) or Invalid data found when processing input(invalid media file).

To answer why, we need to see the operation of ffmpeg's demuxers, which read the multimedia streams from an input file. In this case, we are using "concat", with the following options: (archived docs)

This demuxer accepts the following option:

safe If set to 1, reject unsafe file paths. A file path is considered safe if it does not contain a protocol specification and is relative and all components only contain characters from the portable character set (letters, digits, period, underscore and hyphen) and have no period at the beginning of a component.

If set to 0, any file name is accepted.

The default is 1.

-1 is equivalent to 1 if the format was automatically probed and 0 otherwise.

It turns out find . puts a ./ in front of the file. See How to strip leading "./" in unix "find"? for solutions if you don't want to use -safe 0.