api

MPEG-4编解码的实现(包括MPEG4视音频编解码)

The LAME API

This is the simple interface to the lightweight encoding library
obtained by compiling libmp3lame.a without defining any of
the following extra features:

#define HAVEMPGLIB   to use mpglib's mp3 *decoding* capibility
#define AMIGA_MPEGA  to use mpega.library (Amiga), don't use with HAVEMPGLIB
#define BRHIST       to allow the display of the VBR historgram
#define LIBSNDFILE   to use Erik de Castro Lopo's libsndfile
#define LAMESNDFILE  to use LAME's minimial internal sndfile I/O
#define LAMEPARSE    to use LAME's command line parsing/option setting routines
#define HAVEGTK      to compile in support for the GTK mp3 frame analyzer

To use any of the above features, see lame.h more for details.
For an example of a simple command line interface to lame, see
main.c


=========================================================================

1. (optional) Get the version number of the encoder, if you are interested.  
   lame_version(char *);

2. Initialize the encoder.  sets default for all encoder parameters,
returns pointer to encoder parameters listed above 

   #include "lame.h"
   lame_global_flags gf;
   lame_init(%gf);

Then override various default settings as necessary, for example:

   gf.num_channels=2;
   gf.in_samplerate = 44100;
   gf.brate = 128;
   gf.mode = 0,1 or 3      /* stereo, jstereo, mono */
   gf.quality = 2,5 or 9       /* 2=high, 5=medium 9=low */

see lame.h for the complete list of options.


3. sets more internal configuration based on data provided above:
   lame_init_params(&gf);



4. Encode some data.  input pcm data, output (maybe) mp3 frames.
This routine handles all buffering, resampling and filtering for you.
The required mp3buffer_size can be computed from num_samples, 
samplerate and encoding rate, but here is a worst case estimate:
mp3buffer_size (in bytes) = 1.25*num_samples + 7200
The return code = number of bytes output in mp3buffer.  This can be 0.
If it is -1, an error occured.  

   int lame_encode_buffer(lame_global_flags *gfp,
         short int leftpcm[], short int rightpcm[],
         int num_samples,char *mp3buffer,int  mp3buffer_size);


5. lame_encode_finish will flush the buffers and may return a 
final few mp3 frames.  mp3buffer should be at least 7200 bytes.
return code = number of bytes output to mp3buffer.  This can be 0.

   int lame_encode_finish(lame_global_flags *gfp,char *mp3buffer);