- .loop file doesn't need to exist, used to work with playlist (.m3u, .mtags).
- support "LOOP_CONTENT" in filename.
- filename.ext.loop?LOOP_CONTENT
- filename.ext.loop?type=loopstartlength?LOOPSTART=xxx?LOOPLENGTH=xxx
- filename.ext.loop?type=loopstartlength LOOPSTART=xxx LOOPLENGTH=xxx
- filename.ext.$=[LOOP_CONTENT].loop
- filename.ext.$=[type=loopstartlength LOOPSTART=xxx LOOPLENGTH=xxx].loop
- filename.ext.loop?LOOP_CONTENT