On Tue, Aug 28, 2018 at 08:31:51AM +0200, Marton Balint wrote: > > > On Tue, 28 Aug 2018, Gyan Doshi wrote: > > > > >With some regularity, we have users trying to update input files using > >ffmpeg, usually for the purposes of tagging, but occasionally for changing > >the encoding or something else. Other apps like mp4box or taggers edit the > >files in-place i.e. destination file is same as the source. FFmpeg cannot > >do this. But since these users don't realize that, they will answer Yes to > >the overwrite prompt and then discover their source has been destroyed. > > > >Attached patch checks the URL for file protocol outputs against inputs and > >aborts upon a match. An option is provided for the user to force the > >operation. > > > >The check isn't robust. In particular, it looks for exact url string > >matches, so a command like > > > > ffmpeg -i file:somefile -some_op somefile > > > >will still pass through. But I consider such invocations rare. Most times > >I've seen users trying this (on Stackexchange or other support forums), > >the command is typically of the form, > > > > for i; do ffmpeg -i $i -some_op -y $i > > > >Such a scenario was filed as a bug in #4655 but it was marked as wontfix > >since some protocols/services can manage bidir ops to the same endpoint. > >For that reason, everything other than file protocol sources/sinks are > >exempt i.e. http, pipes, devices..etc. > > > >This patch doesn't affect the semantics of '-y' and adds the check after it. > > Instead of this, maybe we should add support to write lock the files when > opening them for reading. Then ffmpeg can request this. That would be an > useful option, and not just for unexperienced users.
depending on how this is done, it could interfere with reading a file while it is being written/appeneded to by another process [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Good people do not need laws to tell them to act responsibly, while bad people will find a way around the laws. -- Plato
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