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from https://www.poftut.com/ffmpeg-command-tutorial-examples-video-audio/

ffmpeg -i jellyfish-3-mbps-hd-h264.mkv

works in cmd but same on Powershell gives

Unexpected token '-i' in expression or statement.

what's then the right syntax ?

See Question&Answers more detail:os

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As currently shown in your question, the command would work just fine in PowerShell.

# OK - executable name isn't quoted.
ffmpeg -i jellyfish-3-mbps-hd-h264.mkv

However, if you quote the executable path, the problem surfaces.

# FAILS, due to SYNTAX ERROR, because the path is (double)-quoted.
PS> "C:Program Filesffmpeginffmpeg" -i jellyfish-3-mbps-hd-h264.mkv
Unexpected token '-i' in expression or statement.

For syntactic reasons, PowerShell requires &, the call operator, to invoke executables whose paths are quoted and/or contain variable references or subexpressions.

# OK - use of &, the call operator, required because of the quoted path.
& "C:Program Filesffmpeginffmpeg" -i jellyfish-3-mbps-hd-h264.mkv

Or, via an environment variable:

# OK - use of &, the call operator, required because of the variable reference.
# (Double-quoting is optional in this case.)
& $env:ProgramFilesffmpeginffmpeg -i jellyfish-3-mbps-hd-h264.mkv

If you don't want to have to think about when & is actually required, you can simply always use it.

The syntactic need for & stems from PowerShell having two fundamental parsing modes and is explained in detail in this answer.


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