[gmpi] Re: Topic 6: Time representation

>> if you don't supply musical ticks, you have to provide access to the
>> tempo map, which is a much more difficult thing to agree upon: the
>> format and mechanism of access both have to be defined.
>
>You don't necessarily need to provide the tempo map, just a way to ask the
>host to convert from absolute time to musical time.  The host can manage the
>complexities of the tempo map in that case.

yes, and in fact i realize now that just getting musical ticks is more
or less useless without an equivalent "decompress musical time"
conversion anyway (i.e. you really need something like
bars|beats|ticks, not just ticks, to do useful things).

so, my current take on this from the discussion so far is that 

1) we provide process() with:
   
      transport time (frames, int64)
      monotonic sample clock (frames, int64)
      UST (nanoseconds, int64)          

2) we choose one of:

   a) provide process() with musical time (ticks, int64) plus
        a conversion method to get to "structured musical time"
        from musical ticks.

   OR

   b) a conversion method to get "structured musical time" from
        a transport time.

i can't see any use for musical ticks by themselves, so i would tend
to prefer 2b. can anyone see a reason to do 2a?

i would want structured musical time to look something like

  struct {
      int32 bars;        // since transport_time = 0
      int32 beats;       // since start of bar
      int32 ticks;       // since start of beat
      int64 total_ticks; // since transport_time = 0
  };

possibly adding:

      /* information about the current meter */

      float beat_type;        // note divisor (eg. 4 for beat=quarter note)
      float beats_per_bar;    // beats per bar, duh.
      float beats_per_second; // tempo

this information would apply to the time that was passed in for
conversion. one could obviously derive the entire tempo map this way,
though doing so would be very inefficient.

--p




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