Accept float values for --max-fps

Android accepts a float value, there is no reason to limit the option
to be an integer.

In particular, it allows to capture at a rate lower than 1 fps. For
example, to capture 1 frame every 5 seconds:

    scrcpy --video-source=camera --max-fps=0.2

It was already possible to pass a float manually:

    scrcpy --video-source=camera \
        --video-codec-options=max-fps-to-encoder:float=0.2

But accepting a float directly for --max-fps is more convenient.

Refs <https://developer.android.com/reference/android/media/MediaFormat#KEY_MAX_FPS_TO_ENCODER>

app/src/cli.c

@@ -1447,6 +1447,26 @@ parse_integers_arg(const char *s, const char sep, size_t max_items, long *out,
     return count;
 }
 
+static bool
+parse_float_arg(const char *s, float *out, float min, float max,
+                const char *name) {
+    float value;
+    bool ok = sc_str_parse_float(s, &value);
+    if (!ok) {
+        LOGE("Could not parse %s: %s", name, s);
+        return false;
+    }
+
+    if (value < min || value > max) {
+        LOGE("Could not parse %s: value (%f) out-of-range (%f; %f)",
+             name, value, min, max);
+        return false;
+    }
+
+    *out = value;
+    return true;
+}
+
 static bool
 parse_bit_rate(const char *s, uint32_t *bit_rate) {
     long value;
@@ -1474,14 +1494,14 @@ parse_max_size(const char *s, uint16_t *max_size) {
 }
 
 static bool
-parse_max_fps(const char *s, uint16_t *max_fps) {
-    long value;
-    bool ok = parse_integer_arg(s, &value, false, 0, 0xFFFF, "max fps");
+parse_max_fps(const char *s, float *max_fps) {
+    float value;
+    bool ok = parse_float_arg(s, &value, 0, (float) (1 << 16), "max fps");
     if (!ok) {
         return false;
     }
 
-    *max_fps = (uint16_t) value;
+    *max_fps = value;
     return true;
 }
 

app/src/options.h

@@ -240,7 +240,7 @@ struct scrcpy_options {
     uint16_t max_size;
     uint32_t video_bit_rate;
     uint32_t audio_bit_rate;
-    uint16_t max_fps;
+    float max_fps;
     enum sc_lock_video_orientation lock_video_orientation;
     enum sc_orientation display_orientation;
     enum sc_orientation record_orientation;

app/src/server.c

@@ -321,7 +321,7 @@ execute_server(struct sc_server *server,
         ADD_PARAM("max_size=%" PRIu16, params->max_size);
     }
     if (params->max_fps) {
-        ADD_PARAM("max_fps=%" PRIu16, params->max_fps);
+        ADD_PARAM("max_fps=%f" , params->max_fps);
     }
     if (params->lock_video_orientation != SC_LOCK_VIDEO_ORIENTATION_UNLOCKED) {
         ADD_PARAM("lock_video_orientation=%" PRIi8,

app/src/server.h

@@ -44,7 +44,7 @@ struct sc_server_params {
     uint16_t max_size;
     uint32_t video_bit_rate;
     uint32_t audio_bit_rate;
-    uint16_t max_fps;
+    float max_fps;
     int8_t lock_video_orientation;
     bool control;
     uint32_t display_id;

app/src/util/str.c

@@ -147,6 +147,25 @@ sc_str_parse_integer_with_suffix(const char *s, long *out) {
     return true;
 }
 
+bool
+sc_str_parse_float(const char *s, float *out) {
+    char *endptr;
+    if (*s == '\0') {
+        return false;
+    }
+    errno = 0;
+    float value = strtof(s, &endptr);
+    if (errno == ERANGE) {
+        return false;
+    }
+    if (*endptr != '\0') {
+        return false;
+    }
+
+    *out = value;
+    return true;
+}
+
 bool
 sc_str_list_contains(const char *list, char sep, const char *s) {
     char *p;

app/src/util/str.h

@@ -66,6 +66,14 @@ sc_str_parse_integers(const char *s, const char sep, size_t max_items,
 bool
 sc_str_parse_integer_with_suffix(const char *s, long *out);
 
+/**
+ * `Parse `s` as a float into `out`
+ *
+ * Return true if the conversion succeeded, false otherwise.
+ */
+bool
+sc_str_parse_float(const char *s, float *out);
+
 /**
  * Search `s` in the list separated by `sep`
  *

server/src/main/java/com/genymobile/scrcpy/Options.java

@@ -29,7 +29,7 @@ public class Options {
     private boolean audioDup;
     private int videoBitRate = 8000000;
     private int audioBitRate = 128000;
-    private int maxFps;
+    private float maxFps;
     private int lockVideoOrientation = -1;
     private boolean tunnelForward;
     private Rect crop;
@@ -113,7 +113,7 @@ public class Options {
         return audioBitRate;
     }
 
-    public int getMaxFps() {
+    public float getMaxFps() {
         return maxFps;
     }
 
@@ -321,7 +321,7 @@ public class Options {
                     options.audioBitRate = Integer.parseInt(value);
                     break;
                 case "max_fps":
-                    options.maxFps = Integer.parseInt(value);
+                    options.maxFps = parseFloat("max_fps", value);
                     break;
                 case "lock_video_orientation":
                     options.lockVideoOrientation = Integer.parseInt(value);
@@ -493,4 +493,12 @@ public class Options {
         float floatAr = Float.parseFloat(tokens[0]);
         return CameraAspectRatio.fromFloat(floatAr);
     }
+
+    private static float parseFloat(String key, String value) {
+        try {
+            return Float.parseFloat(value);
+        } catch (NumberFormatException e) {
+            throw new IllegalArgumentException("Invalid float value for " + key + ": \"" + value + "\"");
+        }
+    }
 }

server/src/main/java/com/genymobile/scrcpy/video/SurfaceEncoder.java

@@ -39,7 +39,7 @@ public class SurfaceEncoder implements AsyncProcessor {
     private final String encoderName;
     private final List<CodecOption> codecOptions;
     private final int videoBitRate;
-    private final int maxFps;
+    private final float maxFps;
     private final boolean downsizeOnError;
 
     private boolean firstFrameSent;
@@ -48,8 +48,8 @@ public class SurfaceEncoder implements AsyncProcessor {
     private Thread thread;
     private final AtomicBoolean stopped = new AtomicBoolean();
 
-    public SurfaceEncoder(SurfaceCapture capture, Streamer streamer, int videoBitRate, int maxFps, List<CodecOption> codecOptions, String encoderName,
-            boolean downsizeOnError) {
+    public SurfaceEncoder(SurfaceCapture capture, Streamer streamer, int videoBitRate, float maxFps, List<CodecOption> codecOptions,
+            String encoderName, boolean downsizeOnError) {
         this.capture = capture;
         this.streamer = streamer;
         this.videoBitRate = videoBitRate;
@@ -225,7 +225,7 @@ public class SurfaceEncoder implements AsyncProcessor {
         }
     }
 
-    private static MediaFormat createFormat(String videoMimeType, int bitRate, int maxFps, List<CodecOption> codecOptions) {
+    private static MediaFormat createFormat(String videoMimeType, int bitRate, float maxFps, List<CodecOption> codecOptions) {
         MediaFormat format = new MediaFormat();
         format.setString(MediaFormat.KEY_MIME, videoMimeType);
         format.setInteger(MediaFormat.KEY_BIT_RATE, bitRate);