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Change: Compensate for MIDI transmission time when skipping start of song

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This commit is contained in:
Niels Martin Hansen 2018-06-06 18:20:22 +02:00 committed by Michael Lutz
parent 276192f714
commit 11a846e3d5
2 changed files with 10 additions and 2 deletions
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3
src/music/dmusic.cpp
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@ -693,6 +693,9 @@ static void MidiThreadProc(void *)
current_segment.start_block = bl;
break;
} else {
/* Skip the transmission delay compensation performed in the Win32 MIDI driver.
* The DMusic driver will most likely be used with the MS softsynth, which is not subject to transmission delays.
*/
DEBUG(driver, 2, "DMusic: timer: start from block %d (ticktime %d, realtime %.3f, bytes %d)", (int)bl, (int)block.ticktime, ((int)block.realtime) / 1000.0, (int)preload_bytes);
playback_start_time -= block.realtime * MIDITIME_TO_REFTIME;
break;

9
src/music/win32_m.cpp
View File

@ -184,7 +184,7 @@ void CALLBACK TimerCallback(UINT uTimerID, UINT, DWORD_PTR dwUser, DWORD_PTR, DW
/* find first block after start time and pretend playback started earlier
* this is to allow all blocks prior to the actual start to still affect playback,
* as they may contain important controller and program changes */
size_t preload_bytes = 0;
uint preload_bytes = 0;
for (size_t bl = 0; bl < _midi.current_file.blocks.size(); bl++) {
MidiFile::DataBlock &block = _midi.current_file.blocks[bl];
preload_bytes += block.data.Length();
@ -194,8 +194,13 @@ void CALLBACK TimerCallback(UINT uTimerID, UINT, DWORD_PTR dwUser, DWORD_PTR, DW
_midi.current_segment.start_block = bl;
break;
} else {
/* Calculate offset start time for playback.
* The preload_bytes are used to compensate for delay in transmission over traditional serial MIDI interfaces,
* which have a bitrate of 31,250 bits/sec, and transmit 1+8+1 start/data/stop bits per byte.
* The delay compensation is needed to avoid time-compression of following messages.
*/
DEBUG(driver, 2, "Win32-MIDI: timer: start from block %d (ticktime %d, realtime %.3f, bytes %d)", (int)bl, (int)block.ticktime, ((int)block.realtime) / 1000.0, (int)preload_bytes);
_midi.playback_start_time -= block.realtime / 1000;
_midi.playback_start_time -= block.realtime / 1000 - preload_bytes * 1000 / 3125;
break;
}
}