Are we going to have a release before we start this? Jeremiah
Sent from my Samsung smartphone on AT&T Richard Shann <[email protected]> wrote: >I think the next big step for Denemo will be to get the playback working >in its own thread. > >Below are some ideas for how to do this, first there are some notes >which you can cut out if you already know how the soc code is working. > >8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< >I have studied the soc branch code and made the following notes: > >The playback works by using two threads, one is the >process_thread_func() of the backend chosen (I see alsabackend.c and >dummybackend.c so far) and the other is the queue_thread_func() in >audiointerface.c > >The process_thread_func() creates a mutex and then runs a loop: >the loop gets the system time g_get_current_time() and to it adds 5ms (a >compiler constant called PLAYBACK_INTERVAL). This time is then used for >a timed wait on a condition with the mutex, that is a call to >g_cond_timed_wait(). This means that the thread waits for the condition >process_cond to be signalled or until the 5ms have elapsed. >The g_cond_timed_wait() unlocks the mutex before the thread sleeps and >locks it when it continues. >***Question*** is it ok that the mutex has not been locked for the first >time (and correspondingly, at the end g_mutex_free() is called without >unlocking the mutex, is that ok?). > >Next a check is made for quitting the loop - this is done by making an >atomic access to an int which is set by the alsa_seq_destroy() call. >***Question*** does that need to be an atomic access? The int in >question is just a boolean, so in C it just means that if any of the >bits are set it is true. So it really doesn't matter if another thread >is halfway through setting it. > >Next is code which I think is for MIDI input - I ignore this here. > >Now the playback code continues by getting the current time and >subtracting a value called playback_start_time. This latter value is set >up when starting the playing by getting the system time and subtracting >a value "playback_time" which is kept in audiointerface.c and controlled >by calls to the function update_playback_time() and initialized by >midi_play() to Denemo.gui->si->start_time. This last is the time in >seconds from the start of the piece which the user has set as the time >to start from (e.g. via d-SetPlaybackInterval etc). >So for the case of playing an entire movement, this is zero, and the >playback_start_time is the system time when the play was initiated. > >Back to the loop which the process_thread_func() runs... > >The difference between the current time and the playback_start_time is >called the playback_time and is time in seconds along the midi track >where the next event should be taken from. > >After a check for reset (I ignore that here) an event is read from the >queue. This is the call read_event_from_queue() in audiointerface.c. >This is called with a parameter called until_time which is set to the >playback_time plus 5ms (the PLAYBACK_INTERVAL value again). After >checking for stop play conditions (discuss later) this calls into >eventqueue.c for the function event_queue_read_output(). This checks the >midi event time is < the until_time and returns TRUE and the event if so >otherwise FALSE. >Further events are read until this call to get an event from the queue >fails. >Finally before the loop begins again the playback_time that the backend >has, is "sent back" to audiointerface.c via update_playback_time(). > >8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< 8>< > >This code lacks the flexibility to speed up, slow down or pause the >playback - once the playback_start_time has been fixed the midi events >following that time will be sent out by referencing the current system >time. >This could be changed so that instead of executing g_get_current_time() >the time is obtained from a thread which manages the requests from the >user to pause, change tempo etc. > >Currently, I think there are two examples of how to do this in Denemo. >The first was the one I wrote to allow live change of tempo - very >useful for getting the right tempo by adjusting the slider while the >music is playing. The second I wrote to allow the playback to follow a >user playing along with it. >Only the first of these is easy enough to understand that I still have >it in my head: when the tempo slider is moved all the elapsed times that >are obtained are scaled. To make this work, the playback_start_time has >to be re-calculated - so it is as if we had been playing since then at >the new tempo and had just reached the current playback time. In this >way we do not have to keep a history of all the tempo changes. >The second method of controlling the playback was for following the >player (or conductor). In this case the user is setting a time at which >the playback should pause (unless the user has updated it meanwhile). >I am not sure if these could be unified. > >What would the new time-control thread look like? Well, for all the >paused time it could add up the total of pauses so far and subtract >these from the time value it returns. While actually in a pause, I guess >it would just keep returning the same time - only when the pause is >ended would it increment the total amount of pause time and subtract >that from the time value it would otherwise return. I guess it could >also manage the tempo change signal, adjusting the playback_start_time >and scaling the times it returns. Perhaps though, it should be returning >not absolute times but times since start? So it would be returning 0 >during a pause and a scaled difference of (g_get_current_time() - >playback_start_time) and the total_pause_time. (?) > >I would welcome comments. > >Richard Shann > > > > > > > > > > > > > > > > > > >_______________________________________________ >Denemo-devel mailing list >[email protected] >https://lists.gnu.org/mailman/listinfo/denemo-devel _______________________________________________ Denemo-devel mailing list [email protected] https://lists.gnu.org/mailman/listinfo/denemo-devel
