Add --audio-buffer

Expose an option to add a buffering delay (in milliseconds) before
playing audio.

This is similar to the options --display-buffer and --v4l2-buffer for
video frames.

PR #3757 <Genymobile/scrcpy#3757>

Author: rom1v

app/scrcpy.1

@@ -25,6 +25,12 @@ Encode the audio at the given bit\-rate, expressed in bits/s. Unit suffixes are
 
 Default is 196K (196000).
 
+.TP
+.BI "\-\-audio\-buffer ms
+Add a buffering delay (in milliseconds) before playing audio. This increases latency to compensate for jitter.
+
+Default is 0 (no buffering).
+
 .TP
 .BI "\-\-audio\-codec " name
 Select an audio codec (opus or aac).

app/src/cli.c

@@ -70,6 +70,7 @@ enum {
     OPT_LIST_ENCODERS,
     OPT_LIST_DISPLAYS,
     OPT_REQUIRE_AUDIO,
+    OPT_AUDIO_BUFFER,
 };
 
 struct sc_option {
@@ -119,6 +120,14 @@ static const struct sc_option options[] = {
                 "Unit suffixes are supported: 'K' (x1000) and 'M' (x1000000).\n"
                 "Default is 196K (196000).",
     },
+    {
+        .longopt_id = OPT_AUDIO_BUFFER,
+        .longopt = "audio-buffer",
+        .argdesc = "ms",
+        .text = "Add a buffering delay (in milliseconds) before playing audio. "
+                "This increases latency to compensate for jitter.\n"
+                "Default is 0 (no buffering).",
+    },
     {
         .longopt_id = OPT_AUDIO_CODEC,
         .longopt = "audio-codec",
@@ -1812,6 +1821,11 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
             case OPT_REQUIRE_AUDIO:
                 opts->require_audio = true;
                 break;
+            case OPT_AUDIO_BUFFER:
+                if (!parse_buffering_time(optarg, &opts->audio_buffer)) {
+                    return false;
+                }
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;

app/src/options.c

@@ -43,6 +43,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .display_id = 0,
     .display_buffer = 0,
     .v4l2_buffer = 0,
+    .audio_buffer = 0,
 #ifdef HAVE_USB
     .otg = false,
 #endif

app/src/options.h

@@ -125,6 +125,7 @@ struct scrcpy_options {
     uint32_t display_id;
     sc_tick display_buffer;
     sc_tick v4l2_buffer;
+    sc_tick audio_buffer;
 #ifdef HAVE_USB
     bool otg;
 #endif

app/src/scrcpy.c

@@ -43,6 +43,7 @@ struct scrcpy {
     struct sc_server server;
     struct sc_screen screen;
     struct sc_audio_player audio_player;
+    struct sc_delay_buffer audio_buffer;
     struct sc_demuxer video_demuxer;
     struct sc_demuxer audio_demuxer;
     struct sc_decoder video_decoder;
@@ -694,9 +695,16 @@ scrcpy(struct scrcpy_options *options) {
         sc_frame_source_add_sink(src, &s->screen.frame_sink);
 
         if (options->audio) {
+            struct sc_frame_source *src = &s->audio_decoder.frame_source;
+            if (options->audio_buffer) {
+                sc_delay_buffer_init(&s->audio_buffer, options->audio_buffer,
+                                     false);
+                sc_frame_source_add_sink(src, &s->audio_buffer.frame_sink);
+                src = &s->audio_buffer.frame_source;
+            }
+
             sc_audio_player_init(&s->audio_player);
-            sc_frame_source_add_sink(&s->audio_decoder.frame_source,
-                                     &s->audio_player.frame_sink);
+            sc_frame_source_add_sink(src, &s->audio_player.frame_sink);
         }
     }