I have some video files with the extension .MPEG.
I need them to have the extension .MP4.
I ran a converter program and the files actually grew about 15%.
Experimenting on an unconverted MPEG file, I just changed the file name extension to .MP4.
The file played without any noticeable issues.
What am I missing here???
A file extension is just that, a file extension. Basically it’s just part of the file name and it does not change the content of the file..
MPEG and MPG extensions that are normally used interchangeably, and it is used for files that contain video encoded with the mpeg-1, mpeg-2 or mpeg-4 video codecs.
MP4 specifically is intended for MPEG-4 video.
Renaming a file from MPEG or MPG to MP4 is likely to always playback fine as long as the player used is:
*) associated with the extension (MP4) - unless you specifically open the file with the player rather than double clicking on it
*) able to play the level of MPEG compression employed by the file.
From your question it appears that you want MPEG-4 content, since the target extension you want is MP4. However, if your original file is any variant of MPEG less than version 4, than renaming it to MPEG-4 is going to work fine in most cases because all MPEG-4 capable players can play MPEG-2 just fine :-)
If you end up trying to transcode a MPEG (that is, for instance, already MPEG-4) to MPEG-4 then it is very likely that:
1) the quality will be worse (MPEG is LOSSY)
2) the file might be larger than the original
Use one of these tools to find out what codec is actually used by your MPEG files.