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First shot at new audio data types (int32 and float32). Notable changes: - Converters between types are autogenerated. Instead of making multiple passes over the data with seperate filters for endianess, size, signedness, etc, converting between data types is always one specialized filter. This simplifies SDL_BuildAudioCVT(), which otherwise had a million edge cases with the new types, and makes the actually conversions more CPU cache friendly. Left a stub for adding specific optimized versions of these routines (SSE/MMX/Altivec, assembler, etc) - Autogenerated converters are built by SDL/src/audio/sdlgenaudiocvt.pl. This does not need to be run unless tweaking the code, and thus doesn't need integration into the build system. - Went through all the drivers and tried to weed out all the "Uint16" references that are better specified with the new SDL_AudioFormat typedef. - Cleaned out a bunch of hardcoded bitwise magic numbers and replaced them with new SDL_AUDIO_* macros. - Added initial float32 and int32 support code. Theoretically, existing drivers will push these through converters to get the data they want to feed to the hardware. Still TODO: - Optimize and debug new converters. - Update the CoreAudio backend to accept float32 data directly. - Other backends, too? - SDL_LoadWAV() needs to be updated to support int32 and float32 .wav files (both of which exist and can be generated by 'sox' for testing purposes). - Update the mixer to handle new datatypes. - Optionally update SDL_sound and SDL_mixer, etc.
author Ryan C. Gordon <icculus@icculus.org>
date Thu, 24 Aug 2006 12:10:46 +0000
parents 355632dca928
children
line wrap: on
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<HTML
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><TITLE
>SDL_AudioCVT</TITLE
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><H1
><A
NAME="SDLAUDIOCVT"
></A
>SDL_AudioCVT</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN6884"
></A
><H2
>Name</H2
>SDL_AudioCVT&nbsp;--&nbsp;Audio Conversion Structure</DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN6887"
></A
><H2
>Structure Definition</H2
><PRE
CLASS="PROGRAMLISTING"
>typedef struct{
  int needed;
  Uint16 src_format;
  Uint16 dest_format;
  double rate_incr;
  Uint8 *buf;
  int len;
  int len_cvt;
  int len_mult;
  double len_ratio;
  void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
  int filter_index;
} SDL_AudioCVT;</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN6890"
></A
><H2
>Structure Data</H2
><DIV
CLASS="INFORMALTABLE"
><A
NAME="AEN6892"
></A
><P
></P
><TABLE
BORDER="0"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>needed</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Set to one if the conversion is possible</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>src_format</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Audio format of the source</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>dest_format</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Audio format of the destination</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>rate_incr</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Rate conversion increment</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>buf</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Audio buffer</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Length of the original audio buffer in bytes</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>len_cvt</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Length of converted audio buffer in bytes (calculated)</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>buf</I
></TT
> must be <TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
>*<TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
> bytes in size(calculated)</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>len_ratio</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Final audio size is <TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
>*<TT
CLASS="STRUCTFIELD"
><I
>len_ratio</I
></TT
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>filters[10](..)</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Pointers to functions needed for this conversion</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="STRUCTFIELD"
><I
>filter_index</I
></TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>Current conversion function</TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN6944"
></A
><H2
>Description</H2
><P
>The <SPAN
CLASS="STRUCTNAME"
>SDL_AudioCVT</SPAN
> is used to convert audio data between different formats. A <SPAN
CLASS="STRUCTNAME"
>SDL_AudioCVT</SPAN
> structure is created with the <A
HREF="sdlbuildaudiocvt.html"
><TT
CLASS="FUNCTION"
>SDL_BuildAudioCVT</TT
></A
> function, while the actual conversion is done by the <A
HREF="sdlconvertaudio.html"
><TT
CLASS="FUNCTION"
>SDL_ConvertAudio</TT
></A
> function.</P
><P
>Many of the fields in the <SPAN
CLASS="STRUCTNAME"
>SDL_AudioCVT</SPAN
> structure should be considered private and their function will not be discussed here.</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="TYPE"
>Uint8 *</SPAN
><TT
CLASS="STRUCTFIELD"
><I
>buf</I
></TT
></DT
><DD
><P
>This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure <TT
CLASS="STRUCTFIELD"
><I
>buf</I
></TT
> is large enough. See below.</P
></DD
><DT
><SPAN
CLASS="TYPE"
>int</SPAN
> <TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
></DT
><DD
><P
>This is the length of the original audio data in bytes.</P
></DD
><DT
><SPAN
CLASS="TYPE"
>int</SPAN
> <TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
></DT
><DD
><P
>As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of <TT
CLASS="STRUCTFIELD"
><I
>buf</I
></TT
> should be <TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
>*<TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
>.</P
></DD
><DT
><SPAN
CLASS="TYPE"
>double</SPAN
> <TT
CLASS="STRUCTFIELD"
><I
>len_ratio</I
></TT
></DT
><DD
><P
>When you have finished converting your audio data, you need to know how much of your audio buffer is valid. <TT
CLASS="STRUCTFIELD"
><I
>len</I
></TT
>*<TT
CLASS="STRUCTFIELD"
><I
>len_ratio</I
></TT
> is the size of the converted audio data in bytes. This is very similar to <TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
>, however when the convert audio data is shorter than the original <TT
CLASS="STRUCTFIELD"
><I
>len_mult</I
></TT
> would be 1. <TT
CLASS="STRUCTFIELD"
><I
>len_ratio</I
></TT
>, on the other hand, would be a fractional number between 0 and 1.</P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN6989"
></A
><H2
>See Also</H2
><P
><A
HREF="sdlbuildaudiocvt.html"
><TT
CLASS="FUNCTION"
>SDL_BuildAudioCVT</TT
></A
>,
<A
HREF="sdlconvertaudio.html"
><TT
CLASS="FUNCTION"
>SDL_ConvertAudio</TT
></A
>,
<A
HREF="sdlaudiospec.html"
><SPAN
CLASS="STRUCTNAME"
>SDL_AudioSpec</SPAN
></A
></P
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