splitmuxsink: add a property "location-format-type" to allow filenames with values other than fragment index

Submitted by Abhinav

Link to original bug (#793681)

Description

At present, location property only accepts "%d" format specifier which represents fragment-index. In many cases, it would be helpful to allow specifying other values such as first buffer PTS in filenames.

An additional property for splitmuxsink, called "location-format-type" can be added to specify value type represented by format specifier in location string pattern. For e.g. if user wants to have first buffer's time in filenames, he should be able to specify the same by following property values :

e.g.
max-size-time=120000000000
location=video_%Y-%m-%d_%H:%M:%S
location-format-type=2

Where, location-format-type can specify different format types such as
(1): fragment-index - Fragment Index(Default)
(2): first-buffer-pts - First Buffer PTS

.. and so on

Note:
In plugin version 1.12, a new signal location-format-full was added, which is flexible to support above mentioned requirement, but it requires users to do signal handling stuff. While "first buffer's time" as part of filenames, is a very common requirement, it should be possible to specify by simple configuration, than complex signal handling stuff. This should justify above enhancement proposal.

Version: 1.10.x