our_sdl_audio.h

完整的RTP RTSP代码库

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2004 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Sam Lantinga
    [e-mail]
*/

#ifdef SAVE_RCSID
static char rcsid =
 "@(#) $Id: Our_SDL_audio.h,v 1.5 2004/12/03 23:33:38 wmaycisco Exp $";
#endif

/* Access to the raw audio mixing buffer for the SDL library */

#ifndef _OURSDL_audio_h
#define _OURSDL_audio_h

#include <SDL.h>
#include <SDL_thread.h>
#include <begin_code.h>
/* Set up for C function definitions, even when using C++ */
#ifdef __cplusplus
extern "C" {
#endif

/* Function prototypes */

/* These functions are used internally, and should not be used unless you
 * have a specific need to specify the audio driver you want to use.
 * You should normally use SDL_Init() or SDL_InitSubSystem().
 */
extern DECLSPEC int SDLCALL Our_SDL_AudioInit(const char *driver_name);
extern DECLSPEC void SDLCALL Our_SDL_AudioQuit(void);

/* This function fills the given character buffer with the name of the
 * current audio driver, and returns a pointer to it if the audio driver has
 * been initialized.  It returns NULL if no driver has been initialized.
 */
extern DECLSPEC char * SDLCALL Our_SDL_AudioDriverName(char *namebuf, int maxlen);

/*
 * This function opens the audio device with the desired parameters, and
 * returns 0 if successful, placing the actual hardware parameters in the
 * structure pointed to by 'obtained'.  If 'obtained' is NULL, the audio
 * data passed to the callback function will be guaranteed to be in the
 * requested format, and will be automatically converted to the hardware
 * audio format if necessary.  This function returns -1 if it failed 
 * to open the audio device, or couldn't set up the audio thread.
 *
 * When filling in the desired audio spec structure,
 *  'desired->freq' should be the desired audio frequency in samples-per-second.
 *  'desired->format' should be the desired audio format.
 *  'desired->samples' is the desired size of the audio buffer, in samples.
 *     This number should be a power of two, and may be adjusted by the audio
 *     driver to a value more suitable for the hardware.  Good values seem to
 *     range between 512 and 8096 inclusive, depending on the application and
 *     CPU speed.  Smaller values yield faster response time, but can lead
 *     to underflow if the application is doing heavy processing and cannot
 *     fill the audio buffer in time.  A stereo sample consists of both right
 *     and left channels in LR ordering.
 *     Note that the number of samples is directly related to time by the
 *     following formula:  ms = (samples*1000)/freq
 *  'desired->size' is the size in bytes of the audio buffer, and is
 *     calculated by SDL_OpenAudio().
 *  'desired->silence' is the value used to set the buffer to silence,
 *     and is calculated by SDL_OpenAudio().
 *  'desired->callback' should be set to a function that will be called
 *     when the audio device is ready for more data.  It is passed a pointer
 *     to the audio buffer, and the length in bytes of the audio buffer.
 *     This function usually runs in a separate thread, and so you should
 *     protect data structures that it accesses by calling SDL_LockAudio()
 *     and SDL_UnlockAudio() in your code.
 *  'desired->userdata' is passed as the first parameter to your callback
 *     function.
 *
 * The audio device starts out playing silence when it's opened, and should
 * be enabled for playing by calling SDL_PauseAudio(0) when you are ready
 * for your audio callback function to be called.  Since the audio driver
 * may modify the requested size of the audio buffer, you should allocate
 * any local mixing buffers after you open the audio device.
 */
#define AUDIO_FORMAT_HW_AC3 0xfefe

extern DECLSPEC int SDLCALL Our_SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained);

/*
 * Get the current audio state:
 */
extern DECLSPEC SDL_audiostatus SDLCALL Our_SDL_GetAudioStatus(void);

/*
 * This function pauses and unpauses the audio callback processing.
 * It should be called with a parameter of 0 after opening the audio
 * device to start playing sound.  This is so you can safely initialize
 * data for your callback function after opening the audio device.
 * Silence will be written to the audio device during the pause.
 */
extern DECLSPEC void SDLCALL Our_SDL_PauseAudio(int pause_on);

/*
 * This function takes a source format and rate and a destination format
 * and rate, and initializes the 'cvt' structure with information needed
 * by SDL_ConvertAudio() to convert a buffer of audio data from one format
 * to the other.
 * This function returns 0, or -1 if there was an error.
 */
extern DECLSPEC int SDLCALL Our_SDL_BuildAudioCVT(SDL_AudioCVT *cvt,
		Uint16 src_format, Uint8 src_channels, int src_rate,
		Uint16 dst_format, Uint8 dst_channels, int dst_rate);

/* Once you have initialized the 'cvt' structure using SDL_BuildAudioCVT(),
 * created an audio buffer cvt->buf, and filled it with cvt->len bytes of
 * audio data in the source format, this function will convert it in-place
 * to the desired format.
 * The data conversion may expand the size of the audio data, so the buffer
 * cvt->buf should be allocated after the cvt structure is initialized by
 * SDL_BuildAudioCVT(), and should be cvt->len*cvt->len_mult bytes long.
 */
extern DECLSPEC int SDLCALL Our_SDL_ConvertAudio(SDL_AudioCVT *cvt);

/*
 * This takes two audio buffers of the playing audio format and mixes
 * them, performing addition, volume adjustment, and overflow clipping.
 * The volume ranges from 0 - 128, and should be set to SDL_MIX_MAXVOLUME
 * for full audio volume.  Note this does not change hardware volume.
 * This is provided for convenience -- you can mix your own audio data.
 */
#define SDL_MIX_MAXVOLUME 128
extern DECLSPEC void SDLCALL Our_SDL_MixAudio(Uint8 *dst, const Uint8 *src, Uint32 len, int volume);

/*
 * The lock manipulated by these functions protects the callback function.
 * During a LockAudio/UnlockAudio pair, you can be guaranteed that the
 * callback function is not running.  Do not call these from the callback
 * function or you will cause deadlock.
 */
extern DECLSPEC void SDLCALL Our_SDL_LockAudio(void);
extern DECLSPEC void SDLCALL Our_SDL_UnlockAudio(void);

/*
 * This function shuts down audio processing and closes the audio device.
 */
extern DECLSPEC void SDLCALL Our_SDL_CloseAudio(void);

/*
 * Determine if we have the ability to detect the audio buffer delay
 */
extern DECLSPEC int Our_SDL_HasAudioDelay(void);

/*
 * Determine the audio buffer delay in samples
 */
extern DECLSPEC int Our_SDL_AudioDelay(void);


/* Ends C function definitions when using C++ */
#ifdef __cplusplus
}
#endif
#include <close_code.h>
#endif /* _SDL_audio_h */