Add option --max-fps

Add an option to limit the capture frame rate. It only works for devices
with Android >= 10.

Fixes <https://github.com/Genymobile/scrcpy/issues/488>

app/src/main.c

@@ -50,6 +50,10 @@ static void usage(const char *arg0) {
         "    -h, --help\n"
         "        Print this help.\n"
         "\n"
+        "    --max-fps value\n"
+        "        Limit the frame rate of screen capture (only supported on\n"
+        "        devices with Android >= 10).\n"
+        "\n"
         "    -m, --max-size value\n"
         "        Limit both the width and height of the video to value. The\n"
         "        other dimension is computed so that the device aspect-ratio\n"
@@ -269,6 +273,28 @@ parse_max_size(char *optarg, uint16_t *max_size) {
     return true;
 }
 
+static bool
+parse_max_fps(const char *optarg, uint16_t *max_fps) {
+    char *endptr;
+    if (*optarg == '\0') {
+        LOGE("Max FPS parameter is empty");
+        return false;
+    }
+    long value = strtol(optarg, &endptr, 0);
+    if (*endptr != '\0') {
+        LOGE("Invalid max FPS: %s", optarg);
+        return false;
+    }
+    if (value & ~0xffff) {
+        // in practice, it should not be higher than 60
+        LOGE("Max FPS value is invalid: %ld", value);
+        return false;
+    }
+
+    *max_fps = (uint16_t) value;
+    return true;
+}
+
 static bool
 parse_window_position(char *optarg, int16_t *position) {
     char *endptr;
@@ -374,6 +400,7 @@ guess_record_format(const char *filename) {
 #define OPT_WINDOW_WIDTH          1009
 #define OPT_WINDOW_HEIGHT         1010
 #define OPT_WINDOW_BORDERLESS     1011
+#define OPT_MAX_FPS               1012
 
 static bool
 parse_args(struct args *args, int argc, char *argv[]) {
@@ -383,6 +410,7 @@ parse_args(struct args *args, int argc, char *argv[]) {
         {"crop",                  required_argument, NULL, OPT_CROP},
         {"fullscreen",            no_argument,       NULL, 'f'},
         {"help",                  no_argument,       NULL, 'h'},
+        {"max-fps",               required_argument, NULL, OPT_MAX_FPS},
         {"max-size",              required_argument, NULL, 'm'},
         {"no-control",            no_argument,       NULL, 'n'},
         {"no-display",            no_argument,       NULL, 'N'},
@@ -438,6 +466,11 @@ parse_args(struct args *args, int argc, char *argv[]) {
             case 'h':
                 args->help = true;
                 break;
+            case OPT_MAX_FPS:
+                if (!parse_max_fps(optarg, &opts->max_fps)) {
+                    return false;
+                }
+                break;
             case 'm':
                 if (!parse_max_size(optarg, &opts->max_size)) {
                     return false;

app/src/scrcpy.c

@@ -280,6 +280,7 @@ scrcpy(const struct scrcpy_options *options) {
         .local_port = options->port,
         .max_size = options->max_size,
         .bit_rate = options->bit_rate,
+        .max_fps = options->max_fps,
         .control = options->control,
     };
     if (!server_start(&server, options->serial, &params)) {

app/src/scrcpy.h

@@ -18,6 +18,7 @@ struct scrcpy_options {
     uint16_t port;
     uint16_t max_size;
     uint32_t bit_rate;
+    uint16_t max_fps;
     int16_t window_x;
     int16_t window_y;
     uint16_t window_width;
@@ -43,6 +44,7 @@ struct scrcpy_options {
     .port = DEFAULT_LOCAL_PORT, \
     .max_size = DEFAULT_LOCAL_PORT, \
     .bit_rate = DEFAULT_BIT_RATE, \
+    .max_fps = 0, \
     .window_x = -1, \
     .window_y = -1, \
     .window_width = 0, \

app/src/server.c

@@ -118,8 +118,10 @@ static process_t
 execute_server(struct server *server, const struct server_params *params) {
     char max_size_string[6];
     char bit_rate_string[11];
+    char max_fps_string[6];
     sprintf(max_size_string, "%"PRIu16, params->max_size);
     sprintf(bit_rate_string, "%"PRIu32, params->bit_rate);
+    sprintf(max_fps_string, "%"PRIu16, params->max_fps);
     const char *const cmd[] = {
         "shell",
         "CLASSPATH=/data/local/tmp/" SERVER_FILENAME,
@@ -134,6 +136,7 @@ execute_server(struct server *server, const struct server_params *params) {
         SCRCPY_VERSION,
         max_size_string,
         bit_rate_string,
+        max_fps_string,
         server->tunnel_forward ? "true" : "false",
         params->crop ? params->crop : "-",
         "true", // always send frame meta (packet boundaries + timestamp)

app/src/server.h

@@ -35,6 +35,7 @@ struct server_params {
     uint16_t local_port;
     uint16_t max_size;
     uint32_t bit_rate;
+    uint16_t max_fps;
     bool control;
 };