libmpcodecs/ad_sample.c

   1 // SAMPLE audio decoder - you can use this file as template when creating new codec!
   2
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 #include "config.h"
   8 #include "ad_internal.h"
   9
  10 static const ad_info_t info = {
  11         "Sample audio decoder",  // name of the driver
  12         "sample",    // driver name. should be the same as filename without ad_
  13         "A'rpi",     // writer/maintainer of _this_ file
  14         "",          // writer/maintainer/site of the _codec_
  15         ""           // comments
  16 };
  17
  18 LIBAD_EXTERN(sample)
  19
  20 #include "libsample/sample.h" // include your codec's .h files here
  21
  22 static int preinit(sh_audio_t *sh){
  23   // let's check if the driver is available, return 0 if not.
  24   // (you should do that if you use external lib(s) which is optional)
  25   ...
  26
  27   // there are default values set for buffering, but you can override them:
  28
  29   // minimum output buffer size (should be the uncompressed max. frame size)
  30   sh->audio_out_minsize=4*2*1024; // in this sample, we assume max 4 channels,
  31                                   // 2 bytes/sample and 1024 samples/frame
  32                                   // Default: 8192
  33
  34   // minimum input buffer size (set only if you need input buffering)
  35   // (should be the max compressed frame size)
  36   sh->audio_in_minsize=2048; // Default: 0 (no input buffer)
  37
  38   // if you set audio_in_minsize non-zero, the buffer will be allocated
  39   // before the init() call by the core, and you can access it via
  40   // pointer: sh->audio_in_buffer
  41   // it will free'd after uninit(), so you don't have to use malloc/free here!
  42
  43   // the next few parameters define the audio format (channels, sample type,
  44   // in/out bitrate etc.). it's OK to move these to init() if you can set
  45   // them only after some initialization:
  46
  47   sh->samplesize=2;              // bytes (not bits!) per sample per channel
  48   sh->channels=2;                // number of channels
  49   sh->samplerate=44100;          // samplerate
  50   sh->sample_format=AF_FORMAT_S16_LE; // sample format, see libao2/afmt.h
  51
  52   sh->i_bps=64000/8; // input data rate (compressed bytes per second)
  53   // Note: if you have VBR or unknown input rate, set it to some common or
  54   // average value, instead of zero. it's used to predict time delay of
  55   // buffered compressed bytes, so it must be more-or-less real!
  56
  57 //sh->o_bps=...     // output data rate (uncompressed bytes per second)
  58   // Note: you DON'T need to set o_bps in most cases, as it defaults to:
  59   //   sh->samplesize*sh->channels*sh->samplerate;
  60
  61   // for constant rate compressed QuickTime (.mov files) codecs you MUST
  62   // set the compressed and uncompressed packet size (used by the demuxer):
  63   sh->ds->ss_mul = 34; // compressed packet size
  64   sh->ds->ss_div = 64; // samples per packet
  65
  66   return 1; // return values: 1=OK 0=ERROR
  67 }
  68
  69 static int init(sh_audio_t *sh_audio){
  70   // initialize the decoder, set tables etc...
  71
  72   // you can store HANDLE or private struct pointer at sh->context
  73   // you can access WAVEFORMATEX header at sh->wf
  74
  75   // set sample format/rate parameters if you didn't do it in preinit() yet.
  76
  77   return 1; // return values: 1=OK 0=ERROR
  78 }
  79
  80 static void uninit(sh_audio_t *sh){
  81   // uninit the decoder etc...
  82   // again: you don't have to free() a_in_buffer here! it's done by the core.
  83 }
  84
  85 static int decode_audio(sh_audio_t *sh_audio,unsigned char *buf,int minlen,int maxlen){
  86
  87   // audio decoding. the most important thing :)
  88   // parameters you get:
  89   //  buf = pointer to the output buffer, you have to store uncompressed
  90   //        samples there
  91   //  minlen = requested minimum size (in bytes!) of output. it's just a
  92   //        _recommendation_, you can decode more or less, it just tell you that
  93   //        the caller process needs 'minlen' bytes. if it gets less, it will
  94   //        call decode_audio() again.
  95   //  maxlen = maximum size (bytes) of output. you MUST NOT write more to the
  96   //        buffer, it's the upper-most limit!
  97   //        note: maxlen will be always greater or equal to sh->audio_out_minsize
  98
  99   // now, let's decode...
 100
 101   // you can read the compressed stream using the demux stream functions:
 102   //  demux_read_data(sh->ds, buffer, length) - read 'length' bytes to 'buffer'
 103   //  ds_get_packet(sh->ds, &buffer) - set ptr buffer to next data packet
 104   // (both func return number of bytes or 0 for error)
 105
 106   return len; // return value: number of _bytes_ written to output buffer,
 107               // or -1 for EOF (or uncorrectable error)
 108 }
 109
 110 static int control(sh_audio_t *sh,int cmd,void* arg, ...){
 111     // various optional functions you MAY implement:
 112     switch(cmd){
 113       case ADCTRL_RESYNC_STREAM:
 114         // it is called once after seeking, to resync.
 115         // Note: sh_audio->a_in_buffer_len=0; is done _before_ this call!
 116         ...
 117         return CONTROL_TRUE;
 118       case ADCTRL_SKIP_FRAME:
 119         // it is called to skip (jump over) small amount (1/10 sec or 1 frame)
 120         // of audio data - used to sync audio to video after seeking
 121         // if you don't return CONTROL_TRUE, it will defaults to:
 122         //      ds_fill_buffer(sh_audio->ds);  // skip 1 demux packet
 123         ...
 124         return CONTROL_TRUE;
 125     }
 126   return CONTROL_UNKNOWN;
 127 }