audio_dummy.c

   1 /*
   2  * dummy output driver. This file is part of Shairport.
   3  * Copyright (c) James Laird 2013
   4  * All rights reserved.
   5  *
   6  * Modifications for audio synchronisation
   7  * and related work, copyright (c) Mike Brady 2014 -- 2022
   8  * All rights reserved.
   9  *
  10  * Permission is hereby granted, free of charge, to any person
  11  * obtaining a copy of this software and associated documentation
  12  * files (the "Software"), to deal in the Software without
  13  * restriction, including without limitation the rights to use,
  14  * copy, modify, merge, publish, distribute, sublicense, and/or
  15  * sell copies of the Software, and to permit persons to whom the
  16  * Software is furnished to do so, subject to the following conditions:
  17  *
  18  * The above copyright notice and this permission notice shall be
  19  * included in all copies or substantial portions of the Software.
  20  *
  21  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  22  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  23  * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  24  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  25  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  26  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  27  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  28  * OTHER DEALINGS IN THE SOFTWARE.
  29  */
  30
  31 #include "audio.h"
  32 #include "common.h"
  33 #include <inttypes.h> // for PRId64 and friends
  34 #include <stdio.h>
  35 #include <sys/time.h>
  36 #include <unistd.h>
  37
  38 static int init(__attribute__((unused)) int argc, __attribute__((unused)) char **argv) { return 0; }
  39
  40 static void deinit(void) {}
  41
  42 static void start(int sample_rate, __attribute__((unused)) int sample_format) {
  43   debug(1, "dummy audio output started at %d frames per second.", sample_rate);
  44 }
  45 // clang-format off
  46 // Here is a brief explanation of the parameters:
  47 // sample_type is 'play_samples_are_untimed' or 'play_samples_are_timed' defined in audio.h.
  48 //   untimed samples are typically silence used by Shairport Sync itself to set up synchronisation or to fill for missing packets of audio -- the timestamp and playtime are zero.
  49 //   timed samples come from the client.
  50 // timestamp is the RTP timestamp given to the first frame by the client
  51 // playtime is when the first frame should to be played. It is given in "local time".
  52 // local time is CLOCK_MONOTONIC_RAW if available, or CLOCK_MONOTONIC otherwise, expressed in nanoseconds as an unsigned 64-bit integer (See get_absolute_time_in_ns() in common.c)
  53 // clang-format on
  54
  55 static int play(__attribute__((unused)) void *buf, __attribute__((unused)) int samples,
  56                 int sample_type, uint32_t timestamp, uint64_t playtime) {
  57
  58   // sample code using some of the extra information
  59   if (sample_type == play_samples_are_timed) {
  60     int64_t lead_time = playtime - get_absolute_time_in_ns();
  61     debug(2, "leadtime for frame %u is %" PRId64 " nanoseconds, i.e. %f seconds.", timestamp,
  62           lead_time, 0.000000001 * lead_time);
  63   }
  64
  65   return 0;
  66 }
  67
  68 static void stop(void) { debug(1, "dummy audio stopped\n"); }
  69
  70 audio_output audio_dummy = {.name = "dummy",
  71                             .help = NULL,
  72                             .init = &init,
  73                             .deinit = &deinit,
  74                             .prepare = NULL,
  75                             .start = &start,
  76                             .stop = &stop,
  77                             .is_running = NULL,
  78                             .flush = NULL,
  79                             .delay = NULL,
  80                             .stats = NULL,
  81                             .play = &play,
  82                             .volume = NULL,
  83                             .parameters = NULL,
  84                             .mute = NULL};