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Added option to loop play position back to beginning of audio buffer when a buffer under-run occurs, rather than stalling output as before. This option is now the default behaviour.

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This commit is contained in:
Nik Henson 2011-08-07 23:09:18 +00:00
parent 6c71ec28af
commit 07fd26003e
1 changed files with 84 additions and 28 deletions
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112
Src/OSD/SDL/Audio.cpp
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@ -23,6 +23,7 @@
static bool enabled = true; // True if sound output is enabled
static unsigned latency = 20; // Audio latency to use (ie size of audio buffer) as percentage of max buffer size
static bool underRunLoop = true; // True if should loop back to beginning of buffer on under-run, otherwise sound is just skipped
static unsigned playSamples = 512; // Size (in samples) of callback play buffer
@ -41,20 +42,40 @@ static void PlayCallback(void *data, Uint8 *stream, int len)
{
//printf("PlayCallback(%d)\n", len);
// Get current write position and adjust it if write has wrapped
// Get current write position and adjust it if write has wrapped but play position has not
UINT32 adjWritePos = writePos;
if (writeWrapped)
adjWritePos += audioBufferSize;
// Check if play position overlaps write position (ie buffer under-run)
if (adjWritePos < playPos + len)
if (playPos + len > adjWritePos)
{
// If so, just copy silence to audio output stream and exit
memset(stream, 0, len);
//printf("Audio buffer under-run in PlayCallback\n");
underRuns++;
return;
// See what action to take on under-run
if (underRunLoop)
{
// If loop, then move play position back to beginning of data in buffer
playPos = adjWritePos + BYTES_PER_FRAME;
// Check if play position has moved past end of buffer
if (playPos >= audioBufferSize)
{
// If so, wrap it around to beginning again and reset write wrapped flag
playPos -= audioBufferSize;
writeWrapped = false;
}
else
// Otherwise, set write wrapped flag as will now appear as if write has wrapped but play position has not
writeWrapped = true;
}
else
{
// Otherwise, just copy silence to audio output stream and exit
memset(stream, 0, len);
return;
}
}
INT8* src1;
@ -83,15 +104,21 @@ static void PlayCallback(void *data, Uint8 *stream, int len)
// Check if audio is enabled
if (enabled)
{
// If so, copy play region into audio output stream and blank region out afterwards
// If so, copy play region into audio output stream
memcpy(stream, src1, len1);
memset(src1, 0, len1);
// Also, if not looping on under-runs then blank region out
if (!underRunLoop)
memset(src1, 0, len1);
if (len2)
{
// If region was split into two, copy second half into audio output stream as well and blank region out afterwards
// If region was split into two, copy second half into audio output stream as well
memcpy(stream + len1, src2, len2);
memset(src2, 0, len2);
// Also, if not looping on under-runs then blank region out
if (!underRunLoop)
memset(src2, 0, len2);
}
}
else
@ -104,7 +131,7 @@ static void PlayCallback(void *data, Uint8 *stream, int len)
// Check if play position has moved past end of buffer
if (playPos >= audioBufferSize)
{
// If so, wrap it around to beginning again and reset write wrap flag
// If so, wrap it around to beginning again and reset write wrapped flag
playPos -= audioBufferSize;
writeWrapped = false;
}
@ -128,10 +155,7 @@ BOOL OpenAudio()
{
// Initialize SDL audio sub-system
if (SDL_InitSubSystem(SDL_INIT_AUDIO) != 0)
{
ErrorLog("Unable to initialize SDL audio sub-system: %s\n", SDL_GetError());
return FAIL;
}
return ErrorLog("Unable to initialize SDL audio sub-system: %s\n", SDL_GetError());
// Set up audio specification
SDL_AudioSpec fmt;
@ -145,10 +169,7 @@ BOOL OpenAudio()
// Try opening SDL audio output with that specification
SDL_AudioSpec obtained;
if (SDL_OpenAudio(&fmt, &obtained) < 0)
{
ErrorLog("Unable to open 44.1KHz 2-channel audio with SDL: %s\n", SDL_GetError());
return FAIL;
}
return ErrorLog("Unable to open 44.1KHz 2-channel audio with SDL: %s\n", SDL_GetError());
// Check what buffer sample size was actually obtained, and use that
playSamples = obtained.samples;
@ -157,7 +178,12 @@ BOOL OpenAudio()
audioBufferSize = SAMPLE_RATE * BYTES_PER_SAMPLE * latency / MAX_LATENCY;
int roundBuffer = 2 * playSamples;
audioBufferSize = max<int>(roundBuffer, (audioBufferSize / roundBuffer) * roundBuffer);
audioBuffer = new INT8[audioBufferSize];
audioBuffer = new(std::nothrow) INT8[audioBufferSize];
if (audioBuffer == NULL)
{
float audioBufMB = (float)audioBufferSize / (float)0x100000;
return ErrorLog("Insufficient memory for audio latency buffer (need %1.1f MB).", audioBufMB);
}
memset(audioBuffer, 0, sizeof(INT8) * audioBufferSize);
// Set initial play position to be beginning of buffer and initial write position to be half-way into buffer
@ -200,30 +226,60 @@ void OutputAudio(unsigned numSamples, INT16 *leftBuffer, INT16 *rightBuffer)
UINT32 playEndPos = playPos + BYTES_PER_FRAME;
// Undo any wrap-around of the write position that may have occured to create following ordering: playPos < playEndPos < writePos
if (writePos < playEndPos && writeWrapped)
if (playEndPos > writePos && writeWrapped)
writePos += audioBufferSize;
// If play region has caught up with write position and now overlaps it (ie buffer under-run), then bump write position forward in chunks
// until it is past end of play region
while (writePos < playEndPos)
// Check if play region has caught up with write position and now overlaps it (ie buffer under-run)
if (playEndPos > writePos)
{
//printf("Audio buffer under-run in OutputAudio\n");
underRuns++;
writePos += numBytes;
// See what action to take on under-run
if (underRunLoop)
{
// If loop, then move play position back to beginning of data in buffer
playPos = writePos + numBytes + BYTES_PER_FRAME;
// Check if play position has moved past end of buffer
if (playPos >= audioBufferSize)
{
// If so, wrap it around to beginning again and reset write wrapped flag
playPos -= audioBufferSize;
writeWrapped = false;
}
else
{
// Otherwise, set write wrapped flag as will now appear as if write has wrapped but play position has not
writeWrapped = true;
writePos += audioBufferSize;
}
}
else
{
// Otherwise, bump write position forward in chunks until it is past end of play region
do
{
writePos += numBytes;
}
while (playEndPos > writePos);
}
}
// If write position has caught up with play region and now overlaps it (ie buffer over-run), then discard current chunk of data
// Check if write position has caught up with play region and now overlaps it (ie buffer over-run)
if (writePos + numBytes > playPos + audioBufferSize)
{
//printf("Audio buffer over-run in OutputAudio\n");
overRuns++;
// If so, then discard current chunk of data
goto Finish;
}
// Check if write position has moved past end of buffer
if (writePos >= audioBufferSize)
{
// If so, wrap it around to beginning again and set write wrap flag
// If so, wrap it around to beginning again and set write wrapped flag
writePos -= audioBufferSize;
writeWrapped = true;
}
@ -274,7 +330,7 @@ void OutputAudio(unsigned numSamples, INT16 *leftBuffer, INT16 *rightBuffer)
// Check if write position has moved past end of buffer
if (writePos >= audioBufferSize)
{
// If so wrap it around to beginning again and set write wrap flag
// If so, wrap it around to beginning again and set write wrapped flag
writePos -= audioBufferSize;
writeWrapped = true;
}