These sound files are identical but they play differently
=========================================================

[Published 2023-04-08]

Today I wanted to listen to one of my sound files that I have on my
web server.  This sound file is a flac file that contains an audio
track and nothing else.  I have listened to this file many times
before using mpv so I know exactly what the experience is like.

But today, listening to the file gave me a different experience.
There was an image displayed while the sound was playing.  This
image had nothing to do with the sound playing; the image was a
screenshot of a clock settings window.

I was very surprised.  How did my audio file suddenly include an
unrelated image?  Has someone hacked my server and replaced my
files?  I have this file on my desktop computer too so I compared
their md5 sums.  They were identical.  Sha256 and sha512 were
identical too.  I opened w3m's cache directory (since I used w3m to
download the file) and used the `diff` tool which showed me that the
cached file was identical to the one I have in another directory.
Still when I play the cached file directly using mpv it showed the
image, but not the other file.

I figured out that if I renamed the file, the behavior changed.
Apparently this unrelated image was another cached image that I had
opened using w3m in the past and the sound file just happened to get
the same filename as that image but with a flac extension instead of
png.  Mpv then looks for an image with the same name as the sound
file and displays it while playing, if one is found.

The file I played was cached as ~/.w3m/w3mtmp704-12.flac while there
was an old cached image with name ~/.w3m/w3mtmp704-12.png .  I was
surprised to learn that mpv displays other image files as audio
images if they have the same base name, but changing that would
break a use case so maybe what needs to change is w3m's cache file
naming to always use unique names even if we exclude extension.