I have two .m4v MPEG4-Visual elementary streams which need to be truncated down to a specific length, leaving the same starting point and simply specifying a frame number at which to end.
I have searched in all the places I know to try and find a tool to do this, but so far have been unsuccessful. I have even tried a couple of tools, but they were unable to open the files, presumably because they are elementary streams.
If it becomes absolutely necessary, I will probably be able to do it by hand using a Hex Editor, but a tool would make things so much quicker and easier.