For me "Protocol not found" error was caused by ":" in the output filename. Removing it and then adding back again sounds like a workaround and unnecessary complication. Fortunately I was able to find the solution - just add file: in front of the filename. For example this will work even if $file contains substring like "09:02:21":

ffmpeg -i "$file" -acodec pcm_s16le -vcodec copy "file:${file:r:t}".mov

In the command above only file: part is important in context of this answer; but in case if somebody wonders what ${file:r:t} does, it in zsh shell removes absolute path and extension sub-strings from the $file variable.

For me "Protocol not found" error was caused by ":" in the output filename. Removing it and then adding back again sounds like a workaround and unnecessary complication. Fortunately I was able to find the solution - just add file: in front of the filename. For example this will work even if $file contains substring like "09:02:21":

ffmpeg -i "$file" -acodec pcm_s16le -vcodec copy "file:${file:r:t}".mov

In the command above only file: part is important in context of this answer; but in case if somebody wonders what ${file:r:t} does, it in zsh shell removes absolute path and extension sub-strings from the $file variable. Note that file: was not needed for the input filename in this case but was necessary for the output filename even though both contain multiple ":" characters.