Implement audio forwarding

Use Android Open Accessory 2 to redirect the device audio output to the
computer, creating a new audio input source.

Record this new source and play it to the default output.

<https://source.android.com/devices/accessories/aoa2#audio-support>

README.md

@@ -23,14 +23,15 @@ and extract the following files to a directory accessible from your `PATH`:
 
 Make sure you [enabled adb debugging][enable-adb] on your device(s).
 
-The client requires [FFmpeg] and [LibSDL2].
+The client requires [FFmpeg], [LibSDL2] and [LibUSB].
 
 [adb]: https://developer.android.com/studio/command-line/adb.html
 [enable-adb]: https://developer.android.com/studio/command-line/adb.html#Enabling
 [platform-tools]: https://developer.android.com/studio/releases/platform-tools.html
 [platform-tools-windows]: https://dl.google.com/android/repository/platform-tools-latest-windows.zip
 [ffmpeg]: https://en.wikipedia.org/wiki/FFmpeg
-[LibSDL2]: https://en.wikipedia.org/wiki/Simple_DirectMedia_Layer
+[libsdl2]: https://en.wikipedia.org/wiki/Simple_DirectMedia_Layer
+[libusb]: https://en.wikipedia.org/wiki/Libusb
 
 ## Build and install
 
@@ -44,12 +45,12 @@ Install the required packages from your package manager.
 
 ```bash
 # runtime dependencies
-sudo apt install ffmpeg libsdl2-2.0.0
+sudo apt install ffmpeg libsdl2-2.0.0 libusb-1.0-0
 
 # client build dependencies
 sudo apt install make gcc pkg-config meson \
                  libavcodec-dev libavformat-dev libavutil-dev \
-                 libsdl2-dev
+                 libsdl2-dev libusb-1.0-0-dev
 
 # server build dependencies
 sudo apt install openjdk-8-jdk
@@ -104,7 +105,8 @@ pacman -S mingw-w64-x86_64-SDL2 \
 pacman -S mingw-w64-x86_64-make \
           mingw-w64-x86_64-gcc \
           mingw-w64-x86_64-pkg-config \
-          mingw-w64-x86_64-meson
+          mingw-w64-x86_64-meson \
+          mingw-w64-x86_64-libusb
 ```
 
 For a 32 bits version, replace `x86_64` by `i686`:
@@ -146,7 +148,7 @@ Instead, you may want to build it manually. Install the packages:
 brew install sdl2 ffmpeg
 
 # client build dependencies
-brew install pkg-config meson
+brew install pkg-config meson libusb
 ```
 
 Additionally, if you want to build the server, install Java 8 from Caskroom, and
@@ -274,6 +276,12 @@ To show physical touches while scrcpy is running:
 scrcpy -t
 ```
 
+To enable audio forwarding:
+
+```bash
+scrcpy -a
+```
+
 To run without installing:
 
 ```bash

app/meson.build

@@ -18,6 +18,13 @@ src = [
     'src/tinyxpm.c',
 ]
 
+if get_option('audio_support')
+    src += [
+        'src/aoa.c',
+        'src/audio.c'
+    ]
+endif
+
 dependencies = [
     dependency('libavformat'),
     dependency('libavcodec'),
@@ -25,6 +32,10 @@ dependencies = [
     dependency('sdl2'),
 ]
 
+if get_option('audio_support')
+    dependencies += dependency('libusb-1.0')
+endif
+
 cc = meson.get_compiler('c')
 
 if host_machine.system() == 'windows'
@@ -83,6 +94,9 @@ conf.set('SKIP_FRAMES', get_option('skip_frames'))
 # enable High DPI support
 conf.set('HIDPI_SUPPORT', get_option('hidpi_support'))
 
+# enable audio support (enable audio forwarding with --forward-audio)
+conf.set('AUDIO_SUPPORT', get_option('audio_support'))
+
 configure_file(configuration: conf, output: 'config.h')
 
 src_dir = include_directories('src')

app/src/aoa.c

@@ -0,0 +1,206 @@
+#include "aoa.h"
+
+#include "command.h" // must be first to include "winsock2.h" before "windows.h"
+#include <libusb-1.0/libusb.h>
+#include "log.h"
+
+// <https://source.android.com/devices/accessories/aoa2>
+#define AOA_GET_PROTOCOL     51
+#define AOA_START_ACCESSORY  53
+#define AOA_SET_AUDIO_MODE   58
+
+#define AUDIO_MODE_NO_AUDIO               0
+#define AUDIO_MODE_S16LSB_STEREO_44100HZ  1
+
+#define DEFAULT_TIMEOUT 1000
+
+typedef struct control_params {
+    uint8_t request_type;
+    uint8_t request;
+    uint16_t value;
+    uint16_t index;
+    unsigned char *data;
+    uint16_t length;
+    unsigned int timeout;
+} control_params;
+
+static void log_libusb_error(enum libusb_error errcode) {
+    LOGE("%s", libusb_strerror(errcode));
+}
+
+static SDL_bool control_transfer(libusb_device_handle *handle, control_params *params) {
+    int r = libusb_control_transfer(handle,
+                                    params->request_type,
+                                    params->request,
+                                    params->value,
+                                    params->index,
+                                    params->data,
+                                    params->length,
+                                    params->timeout);
+    if (r < 0) {
+        log_libusb_error(r);
+        return SDL_FALSE;
+    }
+    return SDL_TRUE;
+}
+
+static SDL_bool get_serial(libusb_device *device, struct libusb_device_descriptor *desc, unsigned char *data, int length) {
+
+    libusb_device_handle *handle;
+    int r;
+    if ((r = libusb_open(device, &handle))) {
+        // silently ignore
+        LOGD("USB: cannot open device %04x:%04x (%s)", desc->idVendor, desc->idProduct, libusb_strerror(r));
+        return SDL_FALSE;
+    }
+
+    if (!desc->iSerialNumber) {
+        LOGD("USB: device %04x:%04x has no serial number available", desc->idVendor, desc->idProduct);
+        libusb_close(handle);
+        return SDL_FALSE;
+    }
+
+    if ((r = libusb_get_string_descriptor_ascii(handle, desc->iSerialNumber, data, length)) <= 0) {
+        // silently ignore
+        LOGD("USB: cannot read serial of device %04x:%04x (%s)", desc->idVendor, desc->idProduct, libusb_strerror(r));
+        libusb_close(handle);
+        return SDL_FALSE;
+    }
+    data[length - 1] = '\0'; // just in case
+
+    libusb_close(handle);
+    return SDL_TRUE;
+}
+
+static libusb_device *find_device(const char *serial) {
+    libusb_device **list;
+    libusb_device *found = NULL;
+    ssize_t cnt = libusb_get_device_list(NULL, &list);
+    ssize_t i = 0;
+    if (cnt < 0) {
+        log_libusb_error(cnt);
+        return NULL;
+    }
+    for (i = 0; i < cnt; ++i) {
+        libusb_device *device = list[i];
+
+        struct libusb_device_descriptor desc;
+        libusb_get_device_descriptor(device, &desc);
+
+        char usb_serial[128];
+        if (get_serial(device, &desc, (unsigned char *) usb_serial, sizeof(usb_serial))) {
+            if (!strncmp(serial, usb_serial, sizeof(usb_serial))) {
+                libusb_ref_device(device);
+                found = device;
+                LOGD("USB device with serial %s found: %04x:%04x", serial, desc.idVendor, desc.idProduct);
+                break;
+            }
+        }
+    }
+    libusb_free_device_list(list, 1);
+    return found;
+}
+
+static SDL_bool aoa_get_protocol(libusb_device_handle *handle, uint16_t *version) {
+    unsigned char data[2];
+    control_params params = {
+        .request_type = LIBUSB_ENDPOINT_IN | LIBUSB_REQUEST_TYPE_VENDOR,
+        .request = AOA_GET_PROTOCOL,
+        .value = 0,
+        .index = 0,
+        .data = data,
+        .length = sizeof(data),
+        .timeout = DEFAULT_TIMEOUT
+    };
+    if (control_transfer(handle, &params)) {
+        // little endian
+        *version = (data[1] << 8) | data[0];
+        return SDL_TRUE;
+    }
+    return SDL_FALSE;
+}
+
+static SDL_bool set_audio_mode(libusb_device_handle *handle, uint16_t mode) {
+    control_params params = {
+        .request_type = LIBUSB_ENDPOINT_OUT | LIBUSB_REQUEST_TYPE_VENDOR,
+        .request = AOA_SET_AUDIO_MODE,
+        // <https://source.android.com/devices/accessories/aoa2.html#audio-support>
+        .value = mode,
+        .index = 0, // unused
+        .data = NULL,
+        .length = 0,
+        .timeout = DEFAULT_TIMEOUT
+    };
+    return control_transfer(handle, &params);
+}
+
+static SDL_bool start_accessory(libusb_device_handle *handle) {
+    control_params params = {
+        .request_type = LIBUSB_ENDPOINT_OUT | LIBUSB_REQUEST_TYPE_VENDOR,
+        .request = AOA_START_ACCESSORY,
+        .value = 0, // unused
+        .index = 0, // unused
+        .data = NULL,
+        .length = 0,
+        .timeout = DEFAULT_TIMEOUT
+    };
+    return control_transfer(handle, &params);
+}
+
+SDL_bool aoa_init(void) {
+    return !libusb_init(NULL);
+}
+
+void aoa_exit(void) {
+    libusb_exit(NULL);
+}
+
+SDL_bool aoa_forward_audio(const char *serial, SDL_bool forward) {
+    LOGD("%s audio accessory...", forward ? "Enabling" : "Disabling");
+    libusb_device *device = find_device(serial);
+    if (!device) {
+        LOGE("Cannot find USB device having serial %s", serial);
+        return SDL_FALSE;
+    }
+
+    SDL_bool ret = SDL_FALSE;
+
+    libusb_device_handle *handle;
+    int r = libusb_open(device, &handle);
+    if (r) {
+        log_libusb_error(r);
+        goto finally_unref_device;
+    }
+
+    uint16_t version;
+    if (!aoa_get_protocol(handle, &version)) {
+        LOGE("Cannot get AOA protocol version");
+        goto finally_close_handle;
+    }
+
+    LOGD("Device AOA version: %" PRIu16 "\n", version);
+    if (version < 2) {
+        LOGE("Device does not support AOA 2: %" PRIu16, version);
+        goto finally_close_handle;
+    }
+
+    uint16_t mode = forward ? AUDIO_MODE_S16LSB_STEREO_44100HZ : AUDIO_MODE_NO_AUDIO;
+    if (!set_audio_mode(handle, mode)) {
+        LOGE("Cannot set audio mode: %" PRIu16, mode);
+        goto finally_close_handle;
+    }
+
+    if (!start_accessory(handle)) {
+        LOGE("Cannot start accessory");
+        return SDL_FALSE;
+    }
+
+    ret = SDL_TRUE;
+
+finally_close_handle:
+    libusb_close(handle);
+finally_unref_device:
+    libusb_unref_device(device);
+
+    return ret;
+}

app/src/aoa.h

@@ -0,0 +1,15 @@
+#ifndef AOA_H
+#define AOA_H
+
+#include <SDL2/SDL_stdinc.h>
+
+#define AUDIO_MODE_NO_AUDIO               0
+#define AUDIO_MODE_S16LSB_STEREO_44100HZ  1
+
+SDL_bool aoa_init(void);
+void aoa_exit(void);
+
+// serial must not be NULL
+SDL_bool aoa_forward_audio(const char *serial, SDL_bool forward);
+
+#endif

app/src/audio.c

@@ -0,0 +1,205 @@
+#include "audio.h"
+
+#include <SDL2/SDL.h>
+#include "aoa.h"
+#include "command.h"
+#include "log.h"
+
+SDL_bool sdl_audio_init(void) {
+    if (SDL_InitSubSystem(SDL_INIT_AUDIO)) {
+        LOGC("Could not initialize SDL audio: %s", SDL_GetError());
+        return SDL_FALSE;
+    }
+    return SDL_TRUE;
+}
+
+static void init_audio_spec(SDL_AudioSpec *spec) {
+    SDL_zero(*spec);
+    spec->freq = 44100;
+    spec->format = AUDIO_S16LSB;
+    spec->channels = 2;
+    spec->samples = 1024;
+}
+
+SDL_bool audio_player_init(struct audio_player *player, const char *serial) {
+    player->serial = SDL_strdup(serial);
+    return !!player->serial;
+}
+
+void audio_player_destroy(struct audio_player *player) {
+    SDL_free((void *) player->serial);
+}
+
+static void audio_input_callback(void *userdata, Uint8 *stream, int len) {
+    struct audio_player *player = userdata;
+    if (SDL_QueueAudio(player->output_device, stream, len)) {
+        LOGE("Cannot queue audio: %s", SDL_GetError());
+    }
+}
+
+static int get_matching_audio_device(const char *serial, int count) {
+    for (int i = 0; i < count; ++i) {
+        LOGD("Audio input #%d: %s", i, SDL_GetAudioDeviceName(i, 1));
+    }
+
+    char model[128];
+    int r = adb_read_model(serial, model, sizeof(model));
+    if (r <= 0) {
+        LOGE("Cannot read Android device model");
+        return -1;
+    }
+
+    LOGD("Device model is: %s", model);
+
+    // iterate backwards since the matching device is probably the last one
+    for (int i = count - 1; i >= 0; i--) {
+        // model is a NUL-terminated string
+        const char *name = SDL_GetAudioDeviceName(i, 1);
+        if (strstr(name, model)) {
+            // the device name contains the device model, we found it!
+            return i;
+        }
+    }
+    return -1;
+}
+
+static SDL_AudioDeviceID open_accessory_audio_input(struct audio_player *player) {
+    int count = SDL_GetNumAudioDevices(1);
+    if (!count) {
+        LOGE("No audio input source found");
+        return 0;
+    }
+
+    int selected = get_matching_audio_device(player->serial, count);
+    if (selected == -1) {
+        LOGE("Cannot find the Android accessory audio input source");
+        return 0;
+    }
+
+    const char *selected_name = SDL_GetAudioDeviceName(selected, 1);
+    LOGI("Selecting audio input source: %s", selected_name);
+
+    SDL_AudioSpec spec;
+    init_audio_spec(&spec);
+    spec.callback = audio_input_callback;
+    spec.userdata = player;
+
+    int id = SDL_OpenAudioDevice(selected_name, 1, &spec, NULL, 0);
+    if (!id) {
+        LOGE("Cannot open audio input: %s", SDL_GetError());
+    }
+    return id;
+}
+
+static SDL_AudioDeviceID open_default_audio_output() {
+    SDL_AudioSpec spec;
+    init_audio_spec(&spec);
+    int id = SDL_OpenAudioDevice(NULL, 0, &spec, NULL, 0);
+    if (!id) {
+        LOGE("Cannot open audio output: %s", SDL_GetError());
+    }
+    return id;
+}
+
+SDL_bool audio_player_open(struct audio_player *player) {
+    player->output_device = open_default_audio_output();
+    if (!player->output_device) {
+        return SDL_FALSE;
+    }
+
+    player->input_device = open_accessory_audio_input(player);
+    if (!player->input_device) {
+        SDL_CloseAudioDevice(player->output_device);
+        return SDL_FALSE;
+    }
+
+    return SDL_TRUE;
+}
+
+static void audio_player_set_paused(struct audio_player *player, SDL_bool paused) {
+    SDL_PauseAudioDevice(player->input_device, paused);
+    SDL_PauseAudioDevice(player->output_device, paused);
+}
+
+void audio_player_play(struct audio_player *player) {
+    audio_player_set_paused(player, SDL_FALSE);
+}
+
+void audio_player_pause(struct audio_player *player) {
+    audio_player_set_paused(player, SDL_TRUE);
+}
+
+void audio_player_close(struct audio_player *player) {
+    SDL_CloseAudioDevice(player->input_device);
+    SDL_CloseAudioDevice(player->output_device);
+}
+
+SDL_bool audio_forwarding_start(struct audio_player *player, const char *serial) {
+    if (!aoa_init()) {
+        LOGE("Cannot initialize AOA");
+        return SDL_FALSE;
+    }
+
+    char serialno[128];
+    if (!serial) {
+        LOGD("No serial provided, request it to the device");
+        int r = adb_read_serialno(NULL, serialno, sizeof(serialno));
+        if (r <= 0) {
+            LOGE("Cannot read serial from the device");
+            goto error_aoa_exit;
+        }
+        LOGD("Device serial is %s", serialno);
+        serial = serialno;
+    }
+
+    if (!audio_player_init(player, serial)) {
+        LOGE("Cannot initialize audio player");
+        goto error_aoa_exit;
+    }
+
+    // adb connection will be reset!
+    if (!aoa_forward_audio(player->serial, SDL_TRUE)) {
+        LOGE("AOA audio forwarding failed");
+        goto error_destroy_player;
+    }
+
+    LOGI("Audio accessory enabled");
+
+    if (!sdl_audio_init()) {
+        goto error_disable_audio_forwarding;
+    }
+
+    LOGI("Waiting 2s for USB reconfiguration...");
+    SDL_Delay(2000);
+
+    if (!audio_player_open(player)) {
+        goto error_disable_audio_forwarding;
+    }
+
+    audio_player_play(player);
+    return SDL_TRUE;
+
+error_disable_audio_forwarding:
+    if (!aoa_forward_audio(serial, SDL_FALSE)) {
+        LOGW("Cannot disable audio forwarding");
+    }
+error_destroy_player:
+    audio_player_destroy(player);
+error_aoa_exit:
+    aoa_exit();
+
+    return SDL_FALSE;
+}
+
+void audio_forwarding_stop(struct audio_player *player) {
+    audio_player_close(player);
+
+    if (aoa_forward_audio(player->serial, SDL_FALSE)) {
+        LOGI("Audio forwarding disabled");
+    } else {
+        LOGW("Cannot disable audio forwarding");
+    }
+    aoa_exit();
+
+    audio_player_destroy(player);
+}

app/src/audio.h

@@ -0,0 +1,29 @@
+#ifndef AUDIO_H
+#define AUDIO_H
+
+#include <SDL2/SDL_audio.h>
+#include <SDL2/SDL_stdinc.h>
+
+struct audio_player {
+    const char *serial;
+    SDL_AudioDeviceID input_device;
+    SDL_AudioDeviceID output_device;
+};
+
+SDL_bool sdl_audio_init(void);
+
+// serial must not be NULL
+SDL_bool audio_player_init(struct audio_player *player, const char *serial);
+void audio_player_destroy(struct audio_player *player);
+
+SDL_bool audio_player_open(struct audio_player *player);
+void audio_player_close(struct audio_player *player);
+
+void audio_player_play(struct audio_player *player);
+void audio_player_pause(struct audio_player *player);
+
+// for convenience, these functions handle everything
+SDL_bool audio_forwarding_start(struct audio_player *player, const char *serial);
+void audio_forwarding_stop(struct audio_player *player);
+
+#endif

app/src/command.c

@@ -18,8 +18,7 @@ static inline const char *get_adb_command() {
     return adb_command;
 }
 
-process_t adb_execute(const char *serial, const char *const adb_cmd[], int len) {
-    const char *cmd[len + 4];
+static void fill_cmd(const char *cmd[], const char *serial, const char *const adb_cmd[], int len) {
     int i;
     cmd[0] = get_adb_command();
     if (serial) {
@@ -32,9 +31,21 @@ process_t adb_execute(const char *serial, const char *const adb_cmd[], int len)
 
     memcpy(&cmd[i], adb_cmd, len * sizeof(const char *));
     cmd[len + i] = NULL;
+}
+
+process_t adb_execute(const char *serial, const char *const adb_cmd[], int len) {
+    const char *cmd[len + 4];
+    fill_cmd(cmd, serial, adb_cmd, len);
     return cmd_execute(cmd[0], cmd);
 }
 
+process_t adb_execute_redirect(const char *serial, const char *const adb_cmd[], int len,
+                               pipe_t *pipe_stdin, pipe_t *pipe_stdout, pipe_t *pipe_stderr) {
+    const char *cmd[len + 4];
+    fill_cmd(cmd, serial, adb_cmd, len);
+    return cmd_execute_redirect(cmd[0], cmd, pipe_stdin, pipe_stdout, pipe_stderr);
+}
+
 process_t adb_forward(const char *serial, uint16_t local_port, const char *device_socket_name) {
     char local[4 + 5 + 1]; // tcp:PORT
     char remote[108 + 14 + 1]; // localabstract:NAME
@@ -77,6 +88,40 @@ process_t adb_remove_path(const char *serial, const char *path) {
     return adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd));
 }
 
+static int adb_execute_get_output(const char *serial, const char *const adb_cmd[], int adb_cmd_len,
+                           char *data, size_t data_len, const char *name) {
+    pipe_t pipe_stdout;
+    process_t proc = adb_execute_redirect(serial, adb_cmd, adb_cmd_len, NULL, &pipe_stdout, NULL);
+    if (!process_check_success(proc, name)) {
+        return -1;
+    }
+    int r = read_pipe(pipe_stdout, data, data_len);
+    close_pipe(pipe_stdout);
+    return r;
+}
+
+static int truncate_first_line(char *data, int len) {
+    data[len - 1] = '\0';
+    char *eol = strpbrk(data, "\r\n");
+    if (eol) {
+        *eol = '\0';
+        len = eol - data;
+    }
+    return len;
+}
+
+int adb_read_serialno(const char *serial, char *data, size_t len) {
+    const char *const adb_cmd[] = {"get-serialno"};
+    int r = adb_execute_get_output(serial, adb_cmd, ARRAY_LEN(adb_cmd), data, len, "get-serialno");
+    return r <= 0 ? r : truncate_first_line(data, r);
+}
+
+int adb_read_model(const char *serial, char *data, size_t len) {
+    const char *const adb_cmd[] = {"shell", "getprop", "ro.product.model"};
+    int r = adb_execute_get_output(serial, adb_cmd, ARRAY_LEN(adb_cmd), data, len, "getprop model");
+    return r <= 0 ? r : truncate_first_line(data, r);
+}
+
 SDL_bool process_check_success(process_t proc, const char *name) {
     if (proc == PROCESS_NONE) {
         LOGE("Could not execute \"%s\"", name);

app/src/command.h

@@ -24,19 +24,26 @@
 # define PROCESS_NONE NULL
   typedef HANDLE process_t;
   typedef DWORD exit_code_t;
+  typedef HANDLE pipe_t;
 #else
 # include <sys/types.h>
 # define PROCESS_NONE -1
   typedef pid_t process_t;
   typedef int exit_code_t;
+  typedef int pipe_t;
 #endif
 # define NO_EXIT_CODE -1
 
 process_t cmd_execute(const char *path, const char *const argv[]);
+process_t cmd_execute_redirect(const char *path, const char *const argv[],
+                               pipe_t *pipe_stdin, pipe_t *pipe_stdout, pipe_t *pipe_stderr);
 SDL_bool cmd_terminate(process_t pid);
 SDL_bool cmd_simple_wait(process_t pid, exit_code_t *exit_code);
 
 process_t adb_execute(const char *serial, const char *const adb_cmd[], int len);
+process_t adb_execute_redirect(const char *serial, const char *const adb_cmd[], int len,
+                               pipe_t *pipe_stdin, pipe_t *pipe_stdout, pipe_t *pipe_stderr);
+
 process_t adb_forward(const char *serial, uint16_t local_port, const char *device_socket_name);
 process_t adb_forward_remove(const char *serial, uint16_t local_port);
 process_t adb_reverse(const char *serial, const char *device_socket_name, uint16_t local_port);
@@ -44,8 +51,15 @@ process_t adb_reverse_remove(const char *serial, const char *device_socket_name)
 process_t adb_push(const char *serial, const char *local, const char *remote);
 process_t adb_remove_path(const char *serial, const char *path);
 
+// return number of bytes read (-1 on error)
+int adb_read_serialno(const char *serial, char *data, size_t len);
+int adb_read_model(const char *serial, char *data, size_t len);
+
 // convenience function to wait for a successful process execution
 // automatically log process errors with the provided process name
 SDL_bool process_check_success(process_t process, const char *name);
 
+int read_pipe(pipe_t pipe, char *data, size_t len);
+void close_pipe(pipe_t pipe);
+
 #endif

app/src/main.c

@@ -13,6 +13,9 @@ struct args {
     SDL_bool help;
     SDL_bool version;
     SDL_bool show_touches;
+#ifdef AUDIO_SUPPORT
+    SDL_bool forward_audio;
+#endif
     Uint16 port;
     Uint16 max_size;
     Uint32 bit_rate;
@@ -23,6 +26,12 @@ static void usage(const char *arg0) {
         "Usage: %s [options]\n"
         "\n"
         "Options:\n"
+#ifdef AUDIO_SUPPORT
+        "\n"
+        "    -a, --forward-audio\n"
+        "        Forward audio from the device to the computer over USB\n"
+        "        (experimental).\n"
+#endif
         "\n"
         "    -b, --bit-rate value\n"
         "        Encode the video at the given bit-rate, expressed in bits/s.\n"
@@ -188,6 +197,9 @@ static SDL_bool parse_port(char *optarg, Uint16 *port) {
 
 static SDL_bool parse_args(struct args *args, int argc, char *argv[]) {
     static const struct option long_options[] = {
+#ifdef AUDIO_SUPPORT
+        {"forward-audio", no_argument,       NULL, 'a'},
+#endif
         {"bit-rate",      required_argument, NULL, 'b'},
         {"help",          no_argument,       NULL, 'h'},
         {"max-size",      required_argument, NULL, 'm'},
@@ -198,8 +210,18 @@ static SDL_bool parse_args(struct args *args, int argc, char *argv[]) {
         {NULL,            0,                 NULL, 0  },
     };
     int c;
-    while ((c = getopt_long(argc, argv, "b:hm:p:s:tv", long_options, NULL)) != -1) {
+#ifdef AUDIO_SUPPORT
+# define AUDIO_SHORT_PARAM "a"
+#else
+# define AUDIO_SHORT_PARAM
+#endif
+    while ((c = getopt_long(argc, argv, AUDIO_SHORT_PARAM "b:hm:p:s:tv", long_options, NULL)) != -1) {
         switch (c) {
+#ifdef AUDIO_SUPPORT
+            case 'a':
+                args->forward_audio = SDL_TRUE;
+                break;
+#endif
             case 'b':
                 if (!parse_bit_rate(optarg, &args->bit_rate)) {
                     return SDL_FALSE;
@@ -256,6 +278,9 @@ int main(int argc, char *argv[]) {
         .port = DEFAULT_LOCAL_PORT,
         .max_size = DEFAULT_MAX_SIZE,
         .bit_rate = DEFAULT_BIT_RATE,
+#ifdef AUDIO_SUPPORT
+        .forward_audio = SDL_FALSE,
+#endif
     };
     if (!parse_args(&args, argc, argv)) {
         return 1;
@@ -287,10 +312,15 @@ int main(int argc, char *argv[]) {
         .max_size = args.max_size,
         .bit_rate = args.bit_rate,
         .show_touches = args.show_touches,
+#ifdef AUDIO_SUPPORT
+        .forward_audio = args.forward_audio,
+#endif
     };
     int res = scrcpy(&options) ? 0 : 1;
 
     avformat_network_deinit(); // ignore failure
 
+    SDL_Quit();
+
     return res;
 }

app/src/scrcpy.c

@@ -7,6 +7,8 @@
 #include <sys/time.h>
 #include <SDL2/SDL.h>
 
+#include "aoa.h"
+#include "audio.h"
 #include "command.h"
 #include "common.h"
 #include "controller.h"
@@ -29,6 +31,10 @@ static struct frames frames;
 static struct decoder decoder;
 static struct controller controller;
 
+#ifdef AUDIO_SUPPORT
+static struct audio_player audio_player;
+#endif
+
 static struct input_manager input_manager = {
     .controller = &controller,
     .frames = &frames,
@@ -120,9 +126,8 @@ static void wait_show_touches(process_t process) {
 }
 
 SDL_bool scrcpy(const struct scrcpy_options *options) {
-    if (!server_start(&server, options->serial, options->port,
-                      options->max_size, options->bit_rate)) {
-        return SDL_FALSE;
+    if (!SDL_SetHint(SDL_HINT_NO_SIGNAL_HANDLERS, "1")) {
+        LOGW("Cannot request to keep default signal handlers");
     }
 
     process_t proc_show_touches;
@@ -133,13 +138,23 @@ SDL_bool scrcpy(const struct scrcpy_options *options) {
         show_touches_waited = SDL_FALSE;
     }
 
+#ifdef AUDIO_SUPPORT
+    if (options->forward_audio) {
+        if (!audio_forwarding_start(&audio_player, options->serial)) {
+            return SDL_FALSE;
+        }
+    }
+#endif
+
     SDL_bool ret = SDL_TRUE;
 
-    if (!SDL_SetHint(SDL_HINT_NO_SIGNAL_HANDLERS, "1")) {
-        LOGW("Cannot request to keep default signal handlers");
+    if (!server_start(&server, options->serial, options->port,
+                      options->max_size, options->bit_rate)) {
+        ret = SDL_FALSE;
+        goto finally_disable_audio_forwarding;
     }
 
-    if (!sdl_init_and_configure()) {
+    if (!sdl_video_init()) {
         ret = SDL_FALSE;
         goto finally_destroy_server;
     }
@@ -228,6 +243,12 @@ finally_destroy_server:
     }
 
     server_destroy(&server);
+finally_disable_audio_forwarding:
+#ifdef AUDIO_SUPPORT
+    if (options->forward_audio) {
+        audio_forwarding_stop(&audio_player);
+    }
+#endif
 
     return ret;
 }

app/src/scrcpy.h

@@ -2,6 +2,7 @@
 #define SCRCPY_H
 
 #include <SDL2/SDL_stdinc.h>
+#include "config.h"
 
 struct scrcpy_options {
     const char *serial;
@@ -9,6 +10,9 @@ struct scrcpy_options {
     Uint16 max_size;
     Uint32 bit_rate;
     SDL_bool show_touches;
+#ifdef AUDIO_SUPPORT
+    SDL_bool forward_audio;
+#endif
 };
 
 SDL_bool scrcpy(const struct scrcpy_options *options);

app/src/screen.c

@@ -10,14 +10,12 @@
 
 #define DISPLAY_MARGINS 96
 
-SDL_bool sdl_init_and_configure(void) {
-    if (SDL_Init(SDL_INIT_VIDEO)) {
-        LOGC("Could not initialize SDL: %s", SDL_GetError());
+SDL_bool sdl_video_init(void) {
+    if (SDL_InitSubSystem(SDL_INIT_VIDEO)) {
+        LOGC("Could not initialize SDL video: %s", SDL_GetError());
         return SDL_FALSE;
     }
 
-    atexit(SDL_Quit);
-
     // Use the best available scale quality
     if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "2")) {
         LOGW("Could not enable bilinear filtering");

app/src/screen.h

@@ -35,7 +35,7 @@ struct screen {
 }
 
 // init SDL and set appropriate hints
-SDL_bool sdl_init_and_configure(void);
+SDL_bool sdl_video_init(void);
 
 // initialize default values
 void screen_init(struct screen *screen);

app/src/sys/unix/command.c

@@ -19,6 +19,93 @@ pid_t cmd_execute(const char *path, const char *const argv[]) {
     return pid;
 }
 
+pid_t cmd_execute_redirect(const char *path, const char *const argv[],
+                           int *pipe_stdin, int *pipe_stdout, int *pipe_stderr) {
+    int in[2];
+    int out[2];
+    int err[2];
+    if (pipe_stdin) {
+        if (pipe(in) == -1) {
+            perror("pipe");
+            return -1;
+        }
+    }
+    if (pipe_stdout) {
+        if (pipe(out) == -1) {
+            perror("pipe");
+            // clean up
+            if (pipe_stdin) {
+                close(in[0]);
+                close(in[1]);
+            }
+            return -1;
+        }
+    }
+    if (pipe_stderr) {
+        if (pipe(err) == -1) {
+            perror("pipe");
+            // clean up
+            if (pipe_stdout) {
+                close(out[0]);
+                close(out[1]);
+            }
+            if (pipe_stdin) {
+                close(in[0]);
+                close(in[1]);
+            }
+            return -1;
+        }
+    }
+
+    pid_t pid = fork();
+    if (pid == -1) {
+        perror("fork");
+        return -1;
+    }
+
+    if (pid == 0) {
+        if (pipe_stdin) {
+            if (in[0] != STDIN_FILENO) {
+                dup2(in[0], STDIN_FILENO);
+                close(in[0]);
+            }
+            close(in[1]);
+        }
+        if (pipe_stdout) {
+            if (out[1] != STDOUT_FILENO) {
+                dup2(out[1], STDOUT_FILENO);
+                close(out[1]);
+            }
+            close(out[0]);
+        }
+        if (pipe_stderr) {
+            if (err[1] != STDERR_FILENO) {
+                dup2(err[1], STDERR_FILENO);
+                close(err[1]);
+            }
+            close(err[0]);
+        }
+        execvp(path, (char *const *)argv);
+        perror("exec");
+        _exit(1);
+    }
+
+    if (pipe_stdin) {
+        close(in[0]);
+        *pipe_stdin = in[1];
+    }
+    if (pipe_stdout) {
+        *pipe_stdout = out[0];
+        close(out[1]);
+    }
+    if (pipe_stderr) {
+        *pipe_stderr = err[0];
+        close(err[1]);
+    }
+
+    return pid;
+}
+
 SDL_bool cmd_terminate(pid_t pid) {
     return kill(pid, SIGTERM) != -1;
 }
@@ -37,3 +124,13 @@ SDL_bool cmd_simple_wait(pid_t pid, int *exit_code) {
     }
     return !code;
 }
+
+int read_pipe(int pipe, char *data, size_t len) {
+    return read(pipe, data, len);
+}
+
+void close_pipe(int pipe) {
+    if (close(pipe)) {
+        perror("close pipe");
+    }
+}

app/src/sys/win/command.c

@@ -3,20 +3,27 @@
 #include "log.h"
 #include "strutil.h"
 
+static int build_cmd(char *cmd, size_t len, const char *const argv[]) {
+    // Windows command-line parsing is WTF:
+    // <http://daviddeley.com/autohotkey/parameters/parameters.htm#WINPASS>
+    // only make it work for this very specific program
+    // (don't handle escaping nor quotes)
+    size_t ret = xstrjoin(cmd, argv, ' ', len);
+    if (ret >= len) {
+        LOGE("Command too long (%" PRIsizet " chars)", len - 1);
+        return -1;
+    }
+    return 0;
+}
+
 HANDLE cmd_execute(const char *path, const char *const argv[]) {
     STARTUPINFO si;
     PROCESS_INFORMATION pi;
     memset(&si, 0, sizeof(si));
     si.cb = sizeof(si);
 
-    // Windows command-line parsing is WTF:
-    // <http://daviddeley.com/autohotkey/parameters/parameters.htm#WINPASS>
-    // only make it work for this very specific program
-    // (don't handle escaping nor quotes)
     char cmd[256];
-    size_t ret = xstrjoin(cmd, argv, ' ', sizeof(cmd));
-    if (ret >= sizeof(cmd)) {
-        LOGE("Command too long (%" PRIsizet " chars)", sizeof(cmd) - 1);
+    if (build_cmd(cmd, sizeof(cmd), argv)) {
         return NULL;
     }
 
@@ -27,6 +34,75 @@ HANDLE cmd_execute(const char *path, const char *const argv[]) {
     return pi.hProcess;
 }
 
+HANDLE cmd_execute_redirect(const char *path, const char *const argv[],
+                            HANDLE *pipe_stdin, HANDLE *pipe_stdout, HANDLE *pipe_stderr) {
+    SECURITY_ATTRIBUTES sa;
+    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
+    sa.lpSecurityDescriptor = NULL;
+    sa.bInheritHandle = TRUE;
+
+    HANDLE stdin_read_handle;
+    HANDLE stdout_write_handle;
+    HANDLE stderr_write_handle;
+    if (pipe_stdin) {
+        if (!CreatePipe(&stdin_read_handle, pipe_stdin, &sa, 0)) {
+             perror("pipe");
+             return NULL;
+        }
+    }
+    if (pipe_stdout) {
+        if (!CreatePipe(pipe_stdout, &stdout_write_handle, &sa, 0)) {
+             perror("pipe");
+             // clean up
+             if (pipe_stdin) {
+                CloseHandle(&stdin_read_handle);
+                CloseHandle(pipe_stdin);
+             }
+             return NULL;
+        }
+    }
+    if (pipe_stderr) {
+        if (!CreatePipe(pipe_stderr, &stderr_write_handle, &sa, 0)) {
+            perror("pipe");
+            // clean up
+             if (pipe_stdin) {
+                CloseHandle(&stdin_read_handle);
+                CloseHandle(pipe_stdin);
+             }
+            if (pipe_stdout) {
+                CloseHandle(pipe_stdout);
+                CloseHandle(&stdout_write_handle);
+            }
+        }
+    }
+
+    STARTUPINFO si;
+    PROCESS_INFORMATION pi;
+    memset(&si, 0, sizeof(si));
+    si.cb = sizeof(si);
+    si.dwFlags = STARTF_USESTDHANDLES;
+    if (pipe_stdin) {
+        si.hStdInput = stdin_read_handle;
+    }
+    if (pipe_stdout) {
+        si.hStdOutput = stdout_write_handle;
+    }
+    if (pipe_stderr) {
+        si.hStdError = stderr_write_handle;
+    }
+
+    char cmd[256];
+    if (build_cmd(cmd, sizeof(cmd), argv)) {
+        return NULL;
+    }
+
+    if (!CreateProcess(NULL, cmd, NULL, NULL, TRUE, CREATE_NO_WINDOW, NULL, NULL, &si, &pi)) {
+        return NULL;
+    }
+
+    return pi.hProcess;
+}
+
 SDL_bool cmd_terminate(HANDLE handle) {
     return TerminateProcess(handle, 1) && CloseHandle(handle);
 }
@@ -42,3 +118,17 @@ SDL_bool cmd_simple_wait(HANDLE handle, DWORD *exit_code) {
     }
     return !code;
 }
+
+int read_pipe(HANDLE pipe, char *data, size_t len) {
+    DWORD r;
+    if (!ReadFile(pipe, data, len, &r, NULL)) {
+        return -1;
+    }
+    return r;
+}
+
+void close_pipe(HANDLE pipe) {
+    if (!CloseHandle(pipe)) {
+        LOGW("Cannot close pipe");
+    }
+}

meson_options.txt

@@ -4,3 +4,4 @@ option('prebuilt_server', type: 'string', description: 'Path of the prebuilt ser
 option('override_server_path', type: 'string', description: 'Hardcoded path to find the server at runtime')
 option('skip_frames', type: 'boolean', value: true, description: 'Always display the most recent frame')
 option('hidpi_support', type: 'boolean', value: true, description: 'Enable High DPI support')
+option('audio_support', type: 'boolean', value: true, description: 'Enable audio support')