Only way of getting accurate results is to play each file and calculate every correctly played section (FPS or samplerate). And with VLC this would be somewhat problematic, since you can have inputs that never end (e.g. dshow, net streams) or inputs where duration changes (net streams).
Thats a pretty poor excuse. Honestly, that is the type of logic that says "Because there are exceptions, we will not even attempt to fix the problem."
Even though plenty of people stream stuff, or listen to audio or watch video formats that have broken indices, or otherwise have indeterminate lengths...
the VAST majority of the files played on VLC are simple Mp3s, Avis, Mkvs, and WMVs.
the VAST majority of those files are "intact" and encoded using a common/familiar encoding scheme.
Hence, the VAST majority of the files that are played on VLC have easily determined lengths.
Of the litearally hundreds of thousands of Mp3s I have played (100s of audiobooks along with about 100 gigabytes of music) and thousands of movies and TV shows of varying of varying format I have played...
at least 99.9% of them have DETERMINED lengths that can be displayed in the playlist window, in windows "properties" or even as a tab displayed in windows explorer.
because such an overwhelming majority of content DOES have accurate lengths that can be predetermined without actually opening the file and playing it, I would consider it almost a no-brainer.
I found it shocking that VLC does not have this feature.
for those with undetermined lengths due to WHATEVER factor, simply augment the "total time" with an infinity sign, a little message that explains why the number is incorrect, "00:00:00" or some other obvious indicator that explains to the user that the total time is undetermined.