Support camera size selection using -m/--camera-ar

In addition to --camera-size to specify an explicit size, make it
possible to select the camera size automatically, respecting the maximum
size (already used for display mirroring) and an aspect ratio.

For example, "scrcpy --video-source=camera" followed by:
 - (no additional arguments)
    : mirrors at the maximum size, any a-r
 - -m1920
    : only consider valid sizes having both dimensions not above 1920
 - --camera-ar=4:3
    : only consider valid sizes having an aspect ratio of 4:3 (+/- 10%)
 - -m2048 --camera-ar=1.6
    : only consider valid sizes having both dimensions not above 2048
      and an aspect ratio of 1.6 (+/- 10%)

Co-authored-by: Simon Chan <1330321+yume-chan@users.noreply.github.com>

app/data/bash-completion/scrcpy

@@ -10,10 +10,14 @@ _scrcpy() {
         --audio-source=
         --audio-output-buffer=
         -b --video-bit-rate=
+        --camera-ar=
+        --camera-id=
+        --camera-facing=
+        --camera-size=
         --crop=
         -d --select-usb
         --disable-screensaver
-        --display=
+        --display-id=
         --display-buffer=
         -e --select-tcpip
         -f --fullscreen
@@ -74,6 +78,7 @@ _scrcpy() {
         --video-codec=
         --video-codec-options=
         --video-encoder=
+        --video-source=
         -w --stay-awake
         --window-borderless
         --window-title=
@@ -93,10 +98,18 @@ _scrcpy() {
             COMPREPLY=($(compgen -W 'opus aac raw' -- "$cur"))
             return
             ;;
+        --video-source)
+            COMPREPLY=($(compgen -W 'display camera' -- "$cur"))
+            return
+            ;;
         --audio-source)
             COMPREPLY=($(compgen -W 'output mic' -- "$cur"))
             return
             ;;
+        --camera-facing)
+            COMPREPLY=($(compgen -W 'front back external' -- "$cur"))
+            return
+            ;;
         --lock-video-orientation)
             COMPREPLY=($(compgen -W 'unlocked initial 0 1 2 3' -- "$cur"))
             return
@@ -141,8 +154,11 @@ _scrcpy() {
         |--audio-codec-options \
         |--audio-encoder \
         |--audio-output-buffer \
+        |--camera-ar \
+        |--camera-id \
+        |--camera-size \
         |--crop \
-        |--display \
+        |--display-id \
         |--display-buffer \
         |--max-fps \
         |-m|--max-size \

app/data/zsh-completion/_scrcpy

@@ -17,10 +17,14 @@ arguments=(
     '--audio-source=[Select the audio source]:source:(output mic)'
     '--audio-output-buffer=[Configure the size of the SDL audio output buffer (in milliseconds)]'
     {-b,--video-bit-rate=}'[Encode the video at the given bit-rate]'
+    '--camera-ar=[Select the camera size by its aspect ratio]'
+    '--camera-id=[Specify the camera id to mirror]'
+    '--camera-facing=[Select the device camera by its facing direction]:facing:(front back external)'
+    '--camera-size=[Specify an explicit camera capture size]'
     '--crop=[\[width\:height\:x\:y\] Crop the device screen on the server]'
     {-d,--select-usb}'[Use USB device]'
     '--disable-screensaver[Disable screensaver while scrcpy is running]'
-    '--display=[Specify the display id to mirror]'
+    '--display-id=[Specify the display id to mirror]'
     '--display-buffer=[Add a buffering delay \(in milliseconds\) before displaying]'
     {-e,--select-tcpip}'[Use TCP/IP device]'
     {-f,--fullscreen}'[Start in fullscreen]'
@@ -78,6 +82,7 @@ arguments=(
     '--video-codec=[Select the video codec]:codec:(h264 h265 av1)'
     '--video-codec-options=[Set a list of comma-separated key\:type=value options for the device video encoder]'
     '--video-encoder=[Use a specific MediaCodec video encoder]'
+    '--video-source=[Select the video source]:source:(display camera)'
     {-w,--stay-awake}'[Keep the device on while scrcpy is running, when the device is plugged in]'
     '--window-borderless[Disable window decorations \(display borderless window\)]'
     '--window-title=[Set a custom window title]'

app/scrcpy.1

@@ -75,6 +75,28 @@ Encode the video at the given bit rate, expressed in bits/s. Unit suffixes are s
 
 Default is 8M (8000000).
 
+.TP
+.BI "\-\-camera\-ar " ar
+Select the camera size by its aspect ratio (+/- 10%).
+
+Possible values are "sensor" (use the camera sensor aspect ratio), "<num>:<den>" (e.g. "4:3") and "<value>" (e.g. "1.6").
+
+.TP
+.BI "\-\-camera\-id " id
+Specify the device camera id to mirror.
+
+The available camera ids can be listed by \-\-list\-cameras.
+
+.TP
+.BI "\-\-camera\-facing " facing
+Select the device camera by its facing direction.
+
+Possible values are "front", "back" and "external".
+
+.TP
+.BI "\-\-camera\-size " width\fRx\fIheight
+Specify an explicit camera capture size.
+
 .TP
 .BI "\-\-crop " width\fR:\fIheight\fR:\fIx\fR:\fIy
 Crop the device screen on the server.
@@ -94,7 +116,7 @@ Also see \fB\-e\fR (\fB\-\-select\-tcpip\fR).
 Disable screensaver while scrcpy is running.
 
 .TP
-.BI "\-\-display " id
+.BI "\-\-display\-id " id
 Specify the device display id to mirror.
 
 The available display ids can be listed by \-\-list\-displays.
@@ -432,6 +454,12 @@ Use a specific MediaCodec video encoder (depending on the codec provided by \fB\
 
 The available encoders can be listed by \-\-list\-encoders.
 
+.TP
+.BI "\-\-video\-source " source
+Select the video source (display or camera).
+
+Default is display.
+
 .TP
 .B \-w, \-\-stay-awake
 Keep the device on while scrcpy is running, when the device is plugged in.

app/src/adb/adb.c

@@ -218,8 +218,16 @@ sc_adb_forward(struct sc_intr *intr, const char *serial, uint16_t local_port,
                const char *device_socket_name, unsigned flags) {
     char local[4 + 5 + 1]; // tcp:PORT
     char remote[108 + 14 + 1]; // localabstract:NAME
-    sprintf(local, "tcp:%" PRIu16, local_port);
-    snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+
+    int r = snprintf(local, sizeof(local), "tcp:%" PRIu16, local_port);
+    assert(r >= 0 && (size_t) r < sizeof(local));
+
+    r = snprintf(remote, sizeof(remote), "localabstract:%s",
+                 device_socket_name);
+    if (r < 0 || (size_t) r >= sizeof(remote)) {
+        LOGE("Could not write socket name");
+        return false;
+    }
 
     assert(serial);
     const char *const argv[] =
@@ -233,7 +241,9 @@ bool
 sc_adb_forward_remove(struct sc_intr *intr, const char *serial,
                       uint16_t local_port, unsigned flags) {
     char local[4 + 5 + 1]; // tcp:PORT
-    sprintf(local, "tcp:%" PRIu16, local_port);
+    int r = snprintf(local, sizeof(local), "tcp:%" PRIu16, local_port);
+    assert(r >= 0 && (size_t) r < sizeof(local));
+    (void) r;
 
     assert(serial);
     const char *const argv[] =
@@ -249,8 +259,16 @@ sc_adb_reverse(struct sc_intr *intr, const char *serial,
                unsigned flags) {
     char local[4 + 5 + 1]; // tcp:PORT
     char remote[108 + 14 + 1]; // localabstract:NAME
-    sprintf(local, "tcp:%" PRIu16, local_port);
-    snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+    int r = snprintf(local, sizeof(local), "tcp:%" PRIu16, local_port);
+    assert(r >= 0 && (size_t) r < sizeof(local));
+
+    r = snprintf(remote, sizeof(remote), "localabstract:%s",
+                 device_socket_name);
+    if (r < 0 || (size_t) r >= sizeof(remote)) {
+        LOGE("Could not write socket name");
+        return false;
+    }
+
     assert(serial);
     const char *const argv[] =
         SC_ADB_COMMAND("-s", serial, "reverse", remote, local);
@@ -263,7 +281,12 @@ bool
 sc_adb_reverse_remove(struct sc_intr *intr, const char *serial,
                       const char *device_socket_name, unsigned flags) {
     char remote[108 + 14 + 1]; // localabstract:NAME
-    snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+    int r = snprintf(remote, sizeof(remote), "localabstract:%s",
+                     device_socket_name);
+    if (r < 0 || (size_t) r >= sizeof(remote)) {
+        LOGE("Device socket name too long");
+        return false;
+    }
 
     assert(serial);
     const char *const argv[] =
@@ -333,7 +356,9 @@ bool
 sc_adb_tcpip(struct sc_intr *intr, const char *serial, uint16_t port,
              unsigned flags) {
     char port_string[5 + 1];
-    sprintf(port_string, "%" PRIu16, port);
+    int r = snprintf(port_string, sizeof(port_string), "%" PRIu16, port);
+    assert(r >= 0 && (size_t) r < sizeof(port_string));
+    (void) r;
 
     assert(serial);
     const char *const argv[] =

app/src/cli.c

@@ -32,6 +32,7 @@ enum {
     OPT_WINDOW_BORDERLESS,
     OPT_MAX_FPS,
     OPT_LOCK_VIDEO_ORIENTATION,
+    OPT_DISPLAY,
     OPT_DISPLAY_ID,
     OPT_ROTATION,
     OPT_RENDER_DRIVER,
@@ -85,6 +86,8 @@ enum {
     OPT_LIST_CAMERA_SIZES,
     OPT_CAMERA_ID,
     OPT_CAMERA_SIZE,
+    OPT_CAMERA_FACING,
+    OPT_CAMERA_AR,
 };
 
 struct sc_option {
@@ -201,15 +204,29 @@ static const struct sc_option options[] = {
         .longopt = "bit-rate",
         .argdesc = "value",
     },
+    {
+        .longopt_id = OPT_CAMERA_AR,
+        .longopt = "camera-ar",
+        .argdesc = "ar",
+        .text = "Select the camera size by its aspect ratio (+/- 10%).\n"
+                "Possible values are \"sensor\" (use the camera sensor aspect "
+                "ratio), \"<num>:<den>\" (e.g. \"4:3\") or \"<value>\" (e.g. "
+                "\"1.6\")."
+    },
     {
         .longopt_id = OPT_CAMERA_ID,
-        .longopt = "camera",
+        .longopt = "camera-id",
         .argdesc = "id",
-        .text = "Specify the device camera id to mirror when using "
-                "--video-source=camera.\n"
+        .text = "Specify the device camera id to mirror.\n"
                 "The available camera ids can be listed by:\n"
-                "    scrcpy --list-cameras\n"
-                "Default is \"auto\" (the first one)",
+                "    scrcpy --list-cameras",
+    },
+    {
+        .longopt_id = OPT_CAMERA_FACING,
+        .longopt = "camera-facing",
+        .argdesc = "facing",
+        .text = "Select the device camera by its facing direction.\n"
+                "Possible values are \"front\", \"back\" and \"external\".",
     },
     {
         .longopt_id = OPT_CAMERA_SIZE,
@@ -253,9 +270,15 @@ static const struct sc_option options[] = {
         .text = "Disable screensaver while scrcpy is running.",
     },
     {
-        .longopt_id = OPT_DISPLAY_ID,
+        // deprecated
+        .longopt_id = OPT_DISPLAY,
         .longopt = "display",
         .argdesc = "id",
+    },
+    {
+        .longopt_id = OPT_DISPLAY_ID,
+        .longopt = "display-id",
+        .argdesc = "id",
         .text = "Specify the device display id to mirror.\n"
                 "The available display ids can be listed by:\n"
                 "    scrcpy --list-displays\n"
@@ -1694,6 +1717,34 @@ parse_audio_source(const char *optarg, enum sc_audio_source *source) {
     return false;
 }
 
+static bool
+parse_camera_facing(const char *optarg, enum sc_camera_facing *facing) {
+    if (!strcmp(optarg, "front")) {
+        *facing = SC_CAMERA_FACING_FRONT;
+        return true;
+    }
+
+    if (!strcmp(optarg, "back")) {
+        *facing = SC_CAMERA_FACING_BACK;
+        return true;
+    }
+
+    if (!strcmp(optarg, "external")) {
+        *facing = SC_CAMERA_FACING_EXTERNAL;
+        return true;
+    }
+
+    if (*optarg == '\0') {
+        // Empty string is a valid value (equivalent to not passing the option)
+        *facing = SC_CAMERA_FACING_ANY;
+        return true;
+    }
+
+    LOGE("Unsupported camera facing: %s (expected front, back or external)",
+         optarg);
+    return false;
+}
+
 static bool
 parse_time_limit(const char *s, sc_tick *tick) {
     long value;
@@ -1756,6 +1807,9 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
             case OPT_CROP:
                 opts->crop = optarg;
                 break;
+            case OPT_DISPLAY:
+                LOGW("--display is deprecated, use --display-id instead.");
+                // fall through
             case OPT_DISPLAY_ID:
                 if (!parse_display_id(optarg, &opts->display_id)) {
                     return false;
@@ -2085,12 +2139,20 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
                     return false;
                 }
                 break;
+            case OPT_CAMERA_AR:
+                opts->camera_ar = optarg;
+                break;
             case OPT_CAMERA_ID:
                 opts->camera_id = optarg;
                 break;
             case OPT_CAMERA_SIZE:
                 opts->camera_size = optarg;
                 break;
+            case OPT_CAMERA_FACING:
+                if (!parse_camera_facing(optarg, &opts->camera_facing)) {
+                    return false;
+                }
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;
@@ -2185,27 +2247,44 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
     }
 
     if (opts->video_source == SC_VIDEO_SOURCE_CAMERA) {
+        if (opts->display_id) {
+            LOGE("--display-id is only available with --video-source=display");
+            return false;
+        }
+
         if (opts->lock_video_orientation !=
                 SC_LOCK_VIDEO_ORIENTATION_UNLOCKED) {
             LOGE("--lock-video-orientation is not supported for camera");
             return false;
         }
 
-        if (!opts->camera_id) {
-            LOGE("Camera id must be specified by --camera=ID "
-                 "(list the available ids with --list-cameras)");
+        if (opts->camera_id && opts->camera_facing != SC_CAMERA_FACING_ANY) {
+            LOGE("Could not specify both --camera-id and --camera-facing");
             return false;
         }
 
-        if (!opts->camera_size) {
-            LOGE("Camera size must be specified by --camera-size=WIDTHxHEIGHT");
-            return false;
+        if (opts->camera_size) {
+            if (opts->camera_ar) {
+                LOGE("Could not specify both --camera-size and -m/--max-size");
+                return false;
+            }
+
+            if (opts->camera_ar) {
+                LOGE("Could not specify both --camera-size and --camera-ar");
+                return false;
+            }
         }
 
         if (opts->control) {
             LOGI("Camera video source: control disabled");
             opts->control = false;
         }
+    } else if (opts->camera_id
+            || opts->camera_ar
+            || opts->camera_facing != SC_CAMERA_FACING_ANY
+            || opts->camera_size) {
+        LOGE("Camera options are only available with --video-source=camera");
+        return false;
     }
 
     if (opts->audio && opts->audio_source == SC_AUDIO_SOURCE_AUTO) {

app/src/options.c

@@ -13,6 +13,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .audio_encoder = NULL,
     .camera_id = NULL,
     .camera_size = NULL,
+    .camera_ar = NULL,
     .log_level = SC_LOG_LEVEL_INFO,
     .video_codec = SC_CODEC_H264,
     .audio_codec = SC_CODEC_OPUS,
@@ -21,6 +22,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .record_format = SC_RECORD_FORMAT_AUTO,
     .keyboard_input_mode = SC_KEYBOARD_INPUT_MODE_INJECT,
     .mouse_input_mode = SC_MOUSE_INPUT_MODE_INJECT,
+    .camera_facing = SC_CAMERA_FACING_ANY,
     .port_range = {
         .first = DEFAULT_LOCAL_PORT_RANGE_FIRST,
         .last = DEFAULT_LOCAL_PORT_RANGE_LAST,

app/src/options.h

@@ -55,6 +55,13 @@ enum sc_audio_source {
     SC_AUDIO_SOURCE_MIC,
 };
 
+enum sc_camera_facing {
+    SC_CAMERA_FACING_ANY,
+    SC_CAMERA_FACING_FRONT,
+    SC_CAMERA_FACING_BACK,
+    SC_CAMERA_FACING_EXTERNAL,
+};
+
 enum sc_lock_video_orientation {
     SC_LOCK_VIDEO_ORIENTATION_UNLOCKED = -1,
     // lock the current orientation when scrcpy starts
@@ -125,6 +132,7 @@ struct scrcpy_options {
     const char *audio_encoder;
     const char *camera_id;
     const char *camera_size;
+    const char *camera_ar;
     enum sc_log_level log_level;
     enum sc_codec video_codec;
     enum sc_codec audio_codec;
@@ -133,6 +141,7 @@ struct scrcpy_options {
     enum sc_record_format record_format;
     enum sc_keyboard_input_mode keyboard_input_mode;
     enum sc_mouse_input_mode mouse_input_mode;
+    enum sc_camera_facing camera_facing;
     struct sc_port_range port_range;
     uint32_t tunnel_host;
     uint16_t tunnel_port;

app/src/scrcpy.c

@@ -353,6 +353,7 @@ scrcpy(struct scrcpy_options *options) {
         .audio_codec = options->audio_codec,
         .video_source = options->video_source,
         .audio_source = options->audio_source,
+        .camera_facing = options->camera_facing,
         .crop = options->crop,
         .port_range = options->port_range,
         .tunnel_host = options->tunnel_host,
@@ -374,6 +375,7 @@ scrcpy(struct scrcpy_options *options) {
         .audio_encoder = options->audio_encoder,
         .camera_id = options->camera_id,
         .camera_size = options->camera_size,
+        .camera_ar = options->camera_ar,
         .force_adb_forward = options->force_adb_forward,
         .power_off_on_close = options->power_off_on_close,
         .clipboard_autosync = options->clipboard_autosync,

app/src/server.c

@@ -77,6 +77,7 @@ sc_server_params_destroy(struct sc_server_params *params) {
     free((char *) params->audio_encoder);
     free((char *) params->tcpip_dst);
     free((char *) params->camera_id);
+    free((char *) params->camera_ar);
 }
 
 static bool
@@ -105,6 +106,7 @@ sc_server_params_copy(struct sc_server_params *dst,
     COPY(audio_encoder);
     COPY(tcpip_dst);
     COPY(camera_id);
+    COPY(camera_ar);
 #undef COPY
 
     return true;
@@ -183,6 +185,20 @@ sc_server_get_codec_name(enum sc_codec codec) {
     }
 }
 
+static const char *
+sc_server_get_camera_facing_name(enum sc_camera_facing camera_facing) {
+    switch (camera_facing) {
+        case SC_CAMERA_FACING_FRONT:
+            return "front";
+        case SC_CAMERA_FACING_BACK:
+            return "back";
+        case SC_CAMERA_FACING_EXTERNAL:
+            return "external";
+        default:
+            return NULL;
+    }
+}
+
 static sc_pid
 execute_server(struct sc_server *server,
                const struct sc_server_params *params) {
@@ -285,6 +301,13 @@ execute_server(struct sc_server *server,
     if (params->camera_size) {
         ADD_PARAM("camera_size=%s", params->camera_size);
     }
+    if (params->camera_facing != SC_CAMERA_FACING_ANY) {
+        ADD_PARAM("camera_facing=%s",
+            sc_server_get_camera_facing_name(params->camera_facing));
+    }
+    if (params->camera_ar) {
+        ADD_PARAM("camera_ar=%s", params->camera_ar);
+    }
     if (params->show_touches) {
         ADD_PARAM("show_touches=true");
     }

app/src/server.h

@@ -28,6 +28,7 @@ struct sc_server_params {
     enum sc_codec audio_codec;
     enum sc_video_source video_source;
     enum sc_audio_source audio_source;
+    enum sc_camera_facing camera_facing;
     const char *crop;
     const char *video_codec_options;
     const char *audio_codec_options;
@@ -35,6 +36,7 @@ struct sc_server_params {
     const char *audio_encoder;
     const char *camera_id;
     const char *camera_size;
+    const char *camera_ar;
     struct sc_port_range port_range;
     uint32_t tunnel_host;
     uint16_t tunnel_port;

app/src/usb/hid_keyboard.c

@@ -27,7 +27,8 @@
 // keyboard support, though OS could support more keys via modifying the report
 // desc. 6 should be enough for scrcpy.
 #define HID_KEYBOARD_MAX_KEYS 6
-#define HID_KEYBOARD_EVENT_SIZE (2 + HID_KEYBOARD_MAX_KEYS)
+#define HID_KEYBOARD_EVENT_SIZE \
+    (HID_KEYBOARD_INDEX_KEYS + HID_KEYBOARD_MAX_KEYS)
 
 #define HID_RESERVED 0x00
 #define HID_ERROR_ROLL_OVER 0x01

app/tests/test_str.c

@@ -269,21 +269,25 @@ static void test_parse_integer_with_suffix(void) {
 
     char buf[32];
 
-    sprintf(buf, "%ldk", LONG_MAX / 2000);
+    int r = snprintf(buf, sizeof(buf), "%ldk", LONG_MAX / 2000);
+    assert(r >= 0 && (size_t) r < sizeof(buf));
     ok = sc_str_parse_integer_with_suffix(buf, &value);
     assert(ok);
     assert(value == LONG_MAX / 2000 * 1000);
 
-    sprintf(buf, "%ldm", LONG_MAX / 2000);
+    r = snprintf(buf, sizeof(buf), "%ldm", LONG_MAX / 2000);
+    assert(r >= 0 && (size_t) r < sizeof(buf));
     ok = sc_str_parse_integer_with_suffix(buf, &value);
     assert(!ok);
 
-    sprintf(buf, "%ldk", LONG_MIN / 2000);
+    r = snprintf(buf, sizeof(buf), "%ldk", LONG_MIN / 2000);
+    assert(r >= 0 && (size_t) r < sizeof(buf));
     ok = sc_str_parse_integer_with_suffix(buf, &value);
     assert(ok);
     assert(value == LONG_MIN / 2000 * 1000);
 
-    sprintf(buf, "%ldm", LONG_MIN / 2000);
+    r = snprintf(buf, sizeof(buf), "%ldm", LONG_MIN / 2000);
+    assert(r >= 0 && (size_t) r < sizeof(buf));
     ok = sc_str_parse_integer_with_suffix(buf, &value);
     assert(!ok);
 }

doc/video.md

@@ -143,7 +143,7 @@ If several displays are available on the Android device, it is possible to
 select the display to mirror:
 
 ```bash
-scrcpy --display=1
+scrcpy --display-id=1
 ```
 
 The list of display ids can be retrieved by:

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

@@ -0,0 +1,37 @@
+package com.genymobile.scrcpy;
+
+public class CameraAspectRatio {
+    private static final float SENSOR = -1;
+
+    private float ar;
+
+    private CameraAspectRatio(float ar) {
+        this.ar = ar;
+    }
+
+    public static CameraAspectRatio fromFloat(float ar) {
+        if (ar < 0) {
+            throw new IllegalArgumentException("Invalid aspect ratio: " + ar);
+        }
+        return new CameraAspectRatio(ar);
+    }
+
+    public static CameraAspectRatio fromFraction(int w, int h) {
+        if (w <= 0 || h <= 0) {
+            throw new IllegalArgumentException("Invalid aspect ratio: " + w + ":" + h);
+        }
+        return new CameraAspectRatio((float) w / h);
+    }
+
+    public static CameraAspectRatio sensorAspectRatio() {
+        return new CameraAspectRatio(SENSOR);
+    }
+
+    public boolean isSensor() {
+        return ar == SENSOR;
+    }
+
+    public float getAspectRatio() {
+        return ar;
+    }
+}

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

@@ -4,13 +4,18 @@ import com.genymobile.scrcpy.wrappers.ServiceManager;
 
 import android.annotation.SuppressLint;
 import android.annotation.TargetApi;
+import android.graphics.Rect;
 import android.hardware.camera2.CameraAccessException;
 import android.hardware.camera2.CameraCaptureSession;
+import android.hardware.camera2.CameraCharacteristics;
 import android.hardware.camera2.CameraDevice;
+import android.hardware.camera2.CameraManager;
 import android.hardware.camera2.CaptureFailure;
 import android.hardware.camera2.CaptureRequest;
 import android.hardware.camera2.params.OutputConfiguration;
 import android.hardware.camera2.params.SessionConfiguration;
+import android.hardware.camera2.params.StreamConfigurationMap;
+import android.media.MediaCodec;
 import android.os.Build;
 import android.os.Handler;
 import android.os.HandlerThread;
@@ -18,16 +23,25 @@ import android.view.Surface;
 
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.stream.Stream;
 
 public class CameraCapture extends SurfaceCapture {
 
-    private final String cameraId;
+    private final String explicitCameraId;
+    private final CameraFacing cameraFacing;
     private final Size explicitSize;
+    private int maxSize;
+    private final CameraAspectRatio aspectRatio;
+
+    private String cameraId;
+    private Size size;
 
     private HandlerThread cameraThread;
     private Handler cameraHandler;
@@ -36,9 +50,12 @@ public class CameraCapture extends SurfaceCapture {
 
     private final AtomicBoolean disconnected = new AtomicBoolean();
 
-    public CameraCapture(String cameraId, Size explicitSize) {
-        this.cameraId = cameraId;
+    public CameraCapture(String explicitCameraId, CameraFacing cameraFacing, Size explicitSize, int maxSize, CameraAspectRatio aspectRatio) {
+        this.explicitCameraId = explicitCameraId;
+        this.cameraFacing = cameraFacing;
         this.explicitSize = explicitSize;
+        this.maxSize = maxSize;
+        this.aspectRatio = aspectRatio;
     }
 
     @Override
@@ -49,12 +66,99 @@ public class CameraCapture extends SurfaceCapture {
         cameraExecutor = new HandlerExecutor(cameraHandler);
 
         try {
+            cameraId = selectCamera(explicitCameraId, cameraFacing);
+            if (cameraId == null) {
+                throw new IOException("No matching camera found");
+            }
+
+            size = selectSize(cameraId, explicitSize, maxSize, aspectRatio);
+            if (size == null) {
+                throw new IOException("Could not select camera size");
+            }
+
+            Ln.i("Using camera '" + cameraId + "'");
             cameraDevice = openCamera(cameraId);
         } catch (CameraAccessException | InterruptedException e) {
             throw new IOException(e);
         }
     }
 
+    private static String selectCamera(String explicitCameraId, CameraFacing cameraFacing) throws CameraAccessException {
+        if (explicitCameraId != null) {
+            return explicitCameraId;
+        }
+
+        CameraManager cameraManager = ServiceManager.getCameraManager();
+
+        String[] cameraIds = cameraManager.getCameraIdList();
+        if (cameraFacing == null) {
+            // Use the first one
+            return cameraIds.length > 0 ? cameraIds[0] : null;
+        }
+
+        for (String cameraId : cameraIds) {
+            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
+
+            int facing = characteristics.get(CameraCharacteristics.LENS_FACING);
+            if (cameraFacing.value() == facing) {
+                return cameraId;
+            }
+        }
+
+        // Not found
+        return null;
+    }
+
+    @TargetApi(Build.VERSION_CODES.N)
+    private static Size selectSize(String cameraId, Size explicitSize, int maxSize, CameraAspectRatio aspectRatio) throws CameraAccessException {
+        if (explicitSize != null) {
+            return explicitSize;
+        }
+
+        CameraManager cameraManager = ServiceManager.getCameraManager();
+        CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
+
+        StreamConfigurationMap configs = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
+        android.util.Size[] sizes = configs.getOutputSizes(MediaCodec.class);
+        Stream<android.util.Size> stream = Arrays.stream(sizes);
+        if (maxSize > 0) {
+            stream = stream.filter(it -> it.getWidth() <= maxSize && it.getHeight() <= maxSize);
+        }
+
+        Float targetAspectRatio = resolveAspectRatio(aspectRatio, characteristics);
+        if (targetAspectRatio != null) {
+            stream = stream.filter(it -> {
+                float ar = ((float) it.getWidth() / it.getHeight());
+                float arRatio = ar / targetAspectRatio;
+                // Accept if the aspect ratio is the target aspect ratio + or - 10%
+                return arRatio >= 0.9f && arRatio <= 1.1f;
+            });
+        }
+
+        Optional<android.util.Size> selected = stream.min(
+                Comparator.comparing(android.util.Size::getWidth).thenComparing(android.util.Size::getHeight).reversed());
+        if (selected.isPresent()) {
+            android.util.Size size = selected.get();
+            return new Size(size.getWidth(), size.getHeight());
+        }
+
+        // Not found
+        return null;
+    }
+
+    private static Float resolveAspectRatio(CameraAspectRatio ratio, CameraCharacteristics characteristics) {
+        if (ratio == null) {
+            return null;
+        }
+
+        if (ratio.isSensor()) {
+            Rect activeSize = characteristics.get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE);
+            return (float) activeSize.width() / activeSize.height();
+        }
+
+        return ratio.getAspectRatio();
+    }
+
     @Override
     public void start(Surface surface) throws IOException {
         try {
@@ -80,12 +184,23 @@ public class CameraCapture extends SurfaceCapture {
 
     @Override
     public Size getSize() {
-        return explicitSize;
+        return size;
     }
 
     @Override
-    public boolean setMaxSize(int size) {
-        return false;
+    public boolean setMaxSize(int maxSize) {
+        if (explicitSize != null) {
+            return false;
+        }
+
+        this.maxSize = maxSize;
+        try {
+            size = selectSize(cameraId, null, maxSize, aspectRatio);
+            return true;
+        } catch (CameraAccessException e) {
+            Ln.w("Could not select camera size", e);
+            return false;
+        }
     }
 
     @SuppressLint("MissingPermission")

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

@@ -0,0 +1,31 @@
+package com.genymobile.scrcpy;
+
+import android.hardware.camera2.CameraCharacteristics;
+
+public enum CameraFacing {
+    FRONT("front", CameraCharacteristics.LENS_FACING_FRONT),
+    BACK("back", CameraCharacteristics.LENS_FACING_BACK),
+    EXTERNAL("external", CameraCharacteristics.LENS_FACING_EXTERNAL);
+
+    private final String name;
+    private final int value;
+
+    CameraFacing(String name, int value) {
+        this.name = name;
+        this.value = value;
+    }
+
+    int value() {
+        return value;
+    }
+
+    static CameraFacing findByName(String name) {
+        for (CameraFacing facing : CameraFacing.values()) {
+            if (name.equals(facing.name)) {
+                return facing;
+            }
+        }
+
+        return null;
+    }
+}

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

@@ -54,7 +54,7 @@ public final class LogUtils {
             builder.append("\n    (none)");
         } else {
             for (int id : displayIds) {
-                builder.append("\n    --display=").append(id).append("    (");
+                builder.append("\n    --display-id=").append(id).append("    (");
                 DisplayInfo displayInfo = displayManager.getDisplayInfo(id);
                 if (displayInfo != null) {
                     Size size = displayInfo.getSize();
@@ -90,7 +90,7 @@ public final class LogUtils {
                 builder.append("\n    (none)");
             } else {
                 for (String id : cameraIds) {
-                    builder.append("\n    --video-source=camera --camera=").append(id);
+                    builder.append("\n    --video-source=camera --camera-id=").append(id);
                     CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(id);
                     int facing = characteristics.get(CameraCharacteristics.LENS_FACING);
                     builder.append("    (").append(getCameraFacingName(facing)).append(", ");

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

@@ -26,6 +26,8 @@ public class Options {
     private int displayId;
     private String cameraId;
     private Size cameraSize;
+    private CameraFacing cameraFacing;
+    private CameraAspectRatio cameraAspectRatio;
     private boolean showTouches;
     private boolean stayAwake;
     private List<CodecOption> videoCodecOptions;
@@ -126,6 +128,14 @@ public class Options {
         return cameraSize;
     }
 
+    public CameraFacing getCameraFacing() {
+        return cameraFacing;
+    }
+
+    public CameraAspectRatio getCameraAspectRatio() {
+        return cameraAspectRatio;
+    }
+
     public boolean getShowTouches() {
         return showTouches;
     }
@@ -292,7 +302,9 @@ public class Options {
                     options.tunnelForward = Boolean.parseBoolean(value);
                     break;
                 case "crop":
-                    options.crop = parseCrop(value);
+                    if (!value.isEmpty()) {
+                        options.crop = parseCrop(value);
+                    }
                     break;
                 case "control":
                     options.control = Boolean.parseBoolean(value);
@@ -349,10 +361,28 @@ public class Options {
                     options.listCameraSizes = Boolean.parseBoolean(value);
                     break;
                 case "camera_id":
-                    options.cameraId = value;
+                    if (!value.isEmpty()) {
+                        options.cameraId = value;
+                    }
                     break;
                 case "camera_size":
-                    options.cameraSize = parseSize(value);
+                    if (!value.isEmpty()) {
+                        options.cameraSize = parseSize(value);
+                    }
+                    break;
+                case "camera_facing":
+                    if (!value.isEmpty()) {
+                        CameraFacing facing = CameraFacing.findByName(value);
+                        if (facing == null) {
+                            throw new IllegalArgumentException("Camera facing " + value + " not supported");
+                        }
+                        options.cameraFacing = facing;
+                    }
+                    break;
+                case "camera_ar":
+                    if (!value.isEmpty()) {
+                        options.cameraAspectRatio = parseCameraAspectRatio(value);
+                    }
                     break;
                 case "send_device_meta":
                     options.sendDeviceMeta = Boolean.parseBoolean(value);
@@ -385,9 +415,6 @@ public class Options {
     }
 
     private static Rect parseCrop(String crop) {
-        if (crop.isEmpty()) {
-            return null;
-        }
         // input format: "width:height:x:y"
         String[] tokens = crop.split(":");
         if (tokens.length != 4) {
@@ -401,9 +428,6 @@ public class Options {
     }
 
     private static Size parseSize(String size) {
-        if (size.isEmpty()) {
-            return null;
-        }
         // input format: "<width>x<height>"
         String[] tokens = size.split("x");
         if (tokens.length != 2) {
@@ -413,4 +437,20 @@ public class Options {
         int height = Integer.parseInt(tokens[1]);
         return new Size(width, height);
     }
+
+    private static CameraAspectRatio parseCameraAspectRatio(String ar) {
+        if ("sensor".equals(ar)) {
+            return CameraAspectRatio.sensorAspectRatio();
+        }
+
+        String[] tokens = ar.split(":");
+        if (tokens.length == 2) {
+            int w = Integer.parseInt(tokens[0]);
+            int h = Integer.parseInt(tokens[1]);
+            return CameraAspectRatio.fromFraction(w, h);
+        }
+
+        float floatAr = Float.parseFloat(tokens[0]);
+        return CameraAspectRatio.fromFloat(floatAr);
+    }
 }

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

@@ -138,7 +138,8 @@ public final class Server {
                 if (options.getVideoSource() == VideoSource.DISPLAY) {
                     surfaceCapture = new ScreenCapture(device);
                 } else {
-                    surfaceCapture = new CameraCapture(options.getCameraId(), options.getCameraSize());
+                    surfaceCapture = new CameraCapture(options.getCameraId(), options.getCameraFacing(), options.getCameraSize(),
+                            options.getMaxSize(), options.getCameraAspectRatio());
                 }
                 SurfaceEncoder surfaceEncoder = new SurfaceEncoder(surfaceCapture, videoStreamer, options.getVideoBitRate(), options.getMaxFps(),
                         options.getVideoCodecOptions(), options.getVideoEncoder(), options.getDownsizeOnError());