add a -sync option to activate server-client sync in audio-only mode

README.html

@@ -394,6 +394,15 @@ client drops the connection; since UxPlay-1.58, the option
 <code>-nohold</code> modifies this behavior so that when a new client
 requests a connection, it removes the current client and takes
 over.</p></li>
+<li><p>In Audio-Only mode, use the <code>-sync</code> option to
+synchronize audio on the server with video on the client. This
+introduces a delay that the client adds to account for latency. There is
+an option <code>-al x</code> that sets the audio latency <em>x</em> that
+the server reports to the client that in principle might modify the
+delay a little (this is not clear). Here (non-negative decimal)
+<em>x</em> is given in seconds, default is 0.25. <em>Without the
+<code>-sync</code> option, there is no audio delay, but the client’s
+video lags behind the server’s audio.</em></p></li>
 <li><p>Since UxPlay-1.54, you can display the accompanying “Cover Art”
 from sources like Apple Music in Audio-Only (ALAC) mode: run
 “<code>uxplay -ca &lt;name&gt; &amp;</code>” in the background, then run
@@ -680,6 +689,12 @@ the mirror display (X11) window.</p>
 <p><strong>-nh</strong> Do not append “<span class="citation"
 data-cites="_hostname_">@_hostname_</span>” at the end of the AirPlay
 server name.</p>
+<p><strong>-sync</strong> (In Audio-Only (ALAC)) mode: this option
+synchronizes audio on the server with video on the client, but causes
+the client to add a delay to account for latency, so pausing the stream
+will not take effect immediately. This can be mitigated by using the
+<code>-al</code> audio latency setting to change the latency (default
+0.25 secs) that the server reports to the cient.</p>
 <p><strong>-s wxh</strong> (e.g. -s 1920x1080 , which is the default )
 sets the display resolution (width and height, in pixels). (This may be
 a request made to the AirPlay client, and perhaps will not be the final
@@ -780,8 +795,7 @@ in (decimal) seconds in Audio-only (ALAC), that is reported to the
 client. Values in the range [0.0, 10.0] seconds are allowed, and will be
 converted to a whole number of microseconds. Default is 0.25 sec (250000
 usec). (This replaces the <code>-ao</code> option introduced in v1.62,
-as a workaround for a problem that is now fixed: it is not clear if
-changing the value of <em>x</em> produces any effects, however.)</p>
+as a workaround for a problem that is now fixed).</p>
 <p><strong>-ca <em>filename</em></strong> provides a file (where
 <em>filename</em> can include a full path) used for output of “cover
 art” (from Apple Music, <em>etc.</em>,) in audio-only ALAC mode. This

README.md

@@ -333,6 +333,12 @@ per second. (You can see what framerate is actually streaming by using -vs fpsdi
 its current client until that client drops the connection; since UxPlay-1.58, the option `-nohold` modifies this
 behavior so that when a new client requests a connection, it removes the current client and takes over.
 
+* In Audio-Only mode, use the `-sync` option to synchronize audio on the server with video
+on the client. This introduces a delay that the client adds to account for latency.  There is an 
+option `-al x` that sets the audio latency _x_  that the server reports to the client that in principle
+might modify the delay a little (this is not clear).  Here (non-negative decimal) _x_ is given  in seconds, default
+is 0.25. _Without the `-sync` option, there is no audio delay, but the client's video lags behind the server's audio._
+
 * Since UxPlay-1.54, you can display the accompanying "Cover Art" from sources like Apple Music in Audio-Only (ALAC) mode:
 run "`uxplay -ca <name> &`" in the background, then run a image viewer with an autoreload feature: an example
 is "feh": run "``feh -R 1 <name>``"
@@ -566,6 +572,12 @@ Options:
 
 **-nh** Do not append "@_hostname_" at the end of the AirPlay server name.
 
+**-sync** (In Audio-Only (ALAC)) mode: this option synchronizes audio on the server with video on the client,
+   but causes the client to add a delay to account for latency, so pausing the stream will not take effect
+   immediately.  This can be mitigated by using the `-al` audio latency setting to change the latency (default 0.25 secs)
+   that the server reports to the cient.
+
+
 **-s wxh** (e.g. -s 1920x1080 , which is the default ) sets the display resolution (width and height,
    in pixels).   (This may be a
    request made to the AirPlay client, and perhaps will not
@@ -660,7 +672,7 @@ which will not work if a firewall is running.
 **-al _x_** specifies an audio latency _x_ in (decimal) seconds in Audio-only (ALAC), that is reported to the client.  Values
    in the range [0.0, 10.0] seconds are allowed, and will be converted to a whole number of microseconds.  Default
    is 0.25 sec (250000 usec).   (This replaces the `-ao` option introduced in v1.62, as a workaround for a problem that
-   is now fixed: it is not clear if changing the value of _x_ produces any effects, however.) 
+   is now fixed).
 
 **-ca _filename_** provides a file (where _filename_ can include a full path) used for output of "cover art"
    (from Apple Music, _etc._,) in audio-only ALAC mode.   This file is overwritten with the latest cover art as

README.txt

@@ -397,6 +397,15 @@ for help with this or other problems.
     modifies this behavior so that when a new client requests a
     connection, it removes the current client and takes over.
 
+-   In Audio-Only mode, use the `-sync` option to synchronize audio on
+    the server with video on the client. This introduces a delay that
+    the client adds to account for latency. There is an option `-al x`
+    that sets the audio latency *x* that the server reports to the
+    client that in principle might modify the delay a little (this is
+    not clear). Here (non-negative decimal) *x* is given in seconds,
+    default is 0.25. *Without the `-sync` option, there is no audio
+    delay, but the client's video lags behind the server's audio.*
+
 -   Since UxPlay-1.54, you can display the accompanying "Cover Art" from
     sources like Apple Music in Audio-Only (ALAC) mode: run
     "`uxplay -ca <name> &`" in the background, then run a image viewer
@@ -691,6 +700,13 @@ will also now be the name shown above the mirror display (X11) window.
 **-nh** Do not append "@_hostname_" at the end of the AirPlay server
 name.
 
+**-sync** (In Audio-Only (ALAC)) mode: this option synchronizes audio on
+the server with video on the client, but causes the client to add a
+delay to account for latency, so pausing the stream will not take effect
+immediately. This can be mitigated by using the `-al` audio latency
+setting to change the latency (default 0.25 secs) that the server
+reports to the cient.
+
 **-s wxh** (e.g. -s 1920x1080 , which is the default ) sets the display
 resolution (width and height, in pixels). (This may be a request made to
 the AirPlay client, and perhaps will not be the final resolution you
@@ -801,8 +817,7 @@ Audio-only (ALAC), that is reported to the client. Values in the range
 \[0.0, 10.0\] seconds are allowed, and will be converted to a whole
 number of microseconds. Default is 0.25 sec (250000 usec). (This
 replaces the `-ao` option introduced in v1.62, as a workaround for a
-problem that is now fixed: it is not clear if changing the value of *x*
-produces any effects, however.)
+problem that is now fixed).
 
 **-ca *filename*** provides a file (where *filename* can include a full
 path) used for output of "cover art" (from Apple Music, *etc.*,) in

renderers/audio_renderer.h

@@ -30,7 +30,7 @@ extern "C" {
 #include "../lib/logger.h"
 
 bool gstreamer_init();
-void audio_renderer_init(logger_t *logger, const char* audiosink);
+void audio_renderer_init(logger_t *logger, const char* audiosink, const bool *audio_sync);
 void audio_renderer_start(unsigned char* compression_type);
 void audio_renderer_stop();
 void audio_renderer_render_buffer(unsigned char* data, int *data_len, unsigned short *seqnum, uint64_t *ntp_time);

renderers/audio_renderer_gstreamer.c

@@ -82,7 +82,7 @@ static GstClockTime gst_audio_pipeline_base_time = GST_CLOCK_TIME_NONE;
 static logger_t *logger = NULL;
 const char * format[NFORMATS];
 
-void audio_renderer_init(logger_t *render_logger, const char* audiosink) {
+void audio_renderer_init(logger_t *render_logger, const char* audiosink, const bool* audio_sync) {
     GError *error = NULL;
     GstCaps *caps = NULL;
     GstClock *clock = gst_system_clock_obtain();
@@ -114,7 +114,11 @@ void audio_renderer_init(logger_t *render_logger, const char* audiosink) {
         g_string_append (launch, audiosink);
         switch(i) {
         case 1:  /*ALAC*/
-            g_string_append (launch, " sync=true");
+	    if (*audio_sync) {
+                g_string_append (launch, " sync=true");
+	    } else {
+                g_string_append (launch, " sync=false");
+	    }
             break;
         default:
             g_string_append (launch, " sync=false");

uxplay.1

@@ -13,7 +13,8 @@ UxPlay 1.63: An open\-source AirPlay mirroring (+ audio streaming) server.
 .TP
 \fB\-nh\fR       Do \fBNOT\fR append "@\fIhostname\fR" at end of the AirPlay server name
 .TP
-.B
+\fB\-sync\fR     (In Audio-Only mode) sync audio on server with video on client.
+.TP
 \fB\-s\fR wxh[@r]Set display resolution [refresh_rate] default 1920x1080[@60]
 .TP
 \fB\-o\fR        Set display "overscanned" mode on (not usually needed)

uxplay.cpp

@@ -65,7 +65,7 @@ static std::string server_name = DEFAULT_NAME;
 static dnssd_t *dnssd = NULL;
 static raop_t *raop = NULL;
 static logger_t *render_logger = NULL;
-
+static bool audio_sync = false;
 static bool relaunch_video = false;
 static bool reset_loop = false;
 static unsigned int open_connections= 0;
@@ -359,6 +359,7 @@ static void print_info (char *name) {
     printf("Options:\n");
     printf("-n name   Specify the network name of the AirPlay server\n");
     printf("-nh       Do not add \"@hostname\" at the end of the AirPlay server name\n");
+    printf("-sync     (In Audio-Only mode) sync audio on server with video on client\n");
     printf("-s wxh[@r]Set display resolution [refresh_rate] default 1920x1080[@60]\n");
     printf("-o        Set display \"overscanned\" mode on (not usually needed)\n");
     printf("-fs       Full-screen (only works with X11, Wayland and VAAPI)\n");
@@ -552,6 +553,8 @@ static void parse_arguments (int argc, char *argv[]) {
             server_name = std::string(argv[++i]);
         } else if (arg == "-nh") {
             do_append_hostname = false;
+        } else if (arg == "-sync") {
+            audio_sync = true;
         } else if (arg == "-s") {
             if (!option_has_value(i, argc, argv[i], argv[i+1])) exit(1);
             std::string value(argv[++i]);
@@ -1280,7 +1283,7 @@ int main (int argc, char *argv[]) {
     logger_set_level(render_logger, debug_log ? LOGGER_DEBUG : LOGGER_INFO);
 
     if (use_audio) {
-        audio_renderer_init(render_logger, audiosink.c_str());
+        audio_renderer_init(render_logger, audiosink.c_str(), &audio_sync);
     } else {
         LOGI("audio_disabled");
     }