Ken Blake wrote:
On Thu, 18 Oct 2018 03:13:33 +0700, JJ wrote:

On 17 Oct 2018 15:41:02 GMT, Frank Slootweg wrote:

So this file has a MPEG4 *container*, but the *encoding* is *not*
MPEG4!

So this file has a .mp4 extension, but the video encoding is *not*
MPEG4 and the audio encoding is *not* MP3.

To make things clear...

It's true that file extension is irrelevant to the file contents,

It's not really irrelevant to the file contents. It's very relevant;
it describes what the file contents are.

Yes, that description can be incorrect, and that's probably what you
meant. But it's seldom incorrect, so it's far from being irrelevant.

It was actually *my* comment (That's what you get for killfiling
people for the wrong 'reasons'! :-) c.q. :-( [1] [2]).

The description *can* be correct for some simple cases, but - as I
have explained - the description is not and cannot be unambigous,
because there are too many variables to be put in just three characters.

Example: .mp4 probably implies some form of MPEG4 video encoding, but
*which* one, of the several ones? And *which* audio encoding does it
use?

[1] If you quote an attribution line with my name and quote my text,
then why don't you respond to me?

[2] Have you seen my and Paul's solutions to your killfiling problem?