audio_player WIP

If there is exactly one producer, then it can assume that the remaining
space in the buffer will only increase until it write something.

This assumption may allow the producer to write to the buffer (up to a
known safe size) without any synchronization mechanism, thus allowing
to read and write different parts of the buffer in parallel.

The producer can then commit the write with lock held, and update its
knowledge of the safe empty remaining space.

app/meson.build

@@ -4,6 +4,7 @@ src = [
     'src/adb/adb_device.c',
     'src/adb/adb_parser.c',
     'src/adb/adb_tunnel.c',
+    'src/audio_player.c',
     'src/cli.c',
     'src/clock.c',
     'src/compat.c',
@@ -30,6 +31,7 @@ src = [
     'src/version.c',
     'src/video_buffer.c',
     'src/util/acksync.c',
+    'src/util/bytebuf.c',
     'src/util/file.c',
     'src/util/intmap.c',
     'src/util/intr.c',
@@ -260,6 +262,10 @@ if get_option('buildtype') == 'debug'
         ['test_binary', [
             'tests/test_binary.c',
         ]],
+        ['test_bytebuf', [
+            'tests/test_bytebuf.c',
+            'src/util/bytebuf.c',
+        ]],
         ['test_cbuf', [
             'tests/test_cbuf.c',
         ]],

app/src/audio_player.c

@@ -0,0 +1,150 @@
+#include "audio_player.h"
+
+#include "util/log.h"
+
+/** Downcast frame_sink to sc_v4l2_sink */
+#define DOWNCAST(SINK) container_of(SINK, struct sc_audio_player, frame_sink)
+
+void
+sc_audio_player_sdl_callback(void *userdata, uint8_t *stream, int len_int) {
+    struct sc_audio_player *ap = userdata;
+
+    // This callback is called with the lock used by SDL_AudioDeviceLock(), so
+    // the bytebuf is protected
+
+    assert(len_int > 0);
+    size_t len = len_int;
+
+    size_t read = sc_bytebuf_read_remaining(&ap->buf);
+    if (read) {
+        if (read > len) {
+            read = len;
+        }
+        sc_bytebuf_read(&ap->buf, stream, read);
+    }
+    if (read < len) {
+        // Insert silence
+        memset(stream + read, 0, len - read);
+    }
+}
+
+static SDL_AudioFormat
+sc_audio_player_ffmpeg_to_sdl_format(enum AVSampleFormat format) {
+    switch (format) {
+        case AV_SAMPLE_FMT_S16:
+            return AUDIO_S16;
+        case AV_SAMPLE_FMT_S32:
+            return AUDIO_S32;
+        case AV_SAMPLE_FMT_FLT:
+            return AUDIO_F32;
+        default:
+            LOGE("Unsupported FFmpeg sample format: %s",
+                 av_get_sample_fmt_name(format));
+            return 0;
+    }
+}
+
+static bool
+sc_audio_player_frame_sink_open(struct sc_frame_sink *sink,
+                                const AVCodecContext *ctx) {
+    struct sc_audio_player *ap = DOWNCAST(sink);
+
+    SDL_AudioFormat format =
+        sc_audio_player_ffmpeg_to_sdl_format(ctx->sample_fmt);
+    if (!format) {
+        // error already logged
+        //return false;
+        format = AUDIO_F32; // it's planar, but for now there is only 1 channel
+    }
+    LOGI("%d\n", ctx->sample_rate);
+
+    SDL_AudioSpec desired = {
+        .freq = ctx->sample_rate,
+        .format = format,
+        .channels = 1,
+        .samples = 2048,
+        .callback = sc_audio_player_sdl_callback,
+        .userdata = ap,
+    };
+    SDL_AudioSpec obtained;
+
+    ap->device = SDL_OpenAudioDevice(NULL, 0, &desired, &obtained, 0);
+    if (!ap->device) {
+        LOGE("Could not open audio device: %s", SDL_GetError());
+        return false;
+    }
+
+    SDL_PauseAudioDevice(ap->device, 0);
+
+    return true;
+}
+
+static void
+sc_audio_player_frame_sink_close(struct sc_frame_sink *sink) {
+    struct sc_audio_player *ap = DOWNCAST(sink);
+
+    assert(ap->device);
+    SDL_PauseAudioDevice(ap->device, 1);
+    SDL_CloseAudioDevice(ap->device);
+}
+
+static bool
+sc_audio_player_frame_sink_push(struct sc_frame_sink *sink, const AVFrame *frame) {
+    struct sc_audio_player *ap = DOWNCAST(sink);
+
+    const uint8_t *data = frame->data[0];
+    size_t size = frame->linesize[0];
+
+    // TODO convert to non planar format
+    // TODO then re-enable stereo
+    // TODO clock drift compensation
+
+    // It should almost always be possible to write without lock
+    bool can_write_without_lock = size <= ap->safe_empty_buffer;
+    if (can_write_without_lock) {
+        sc_bytebuf_prepare_write(&ap->buf, data, size);
+    }
+
+    SDL_LockAudioDevice(ap->device);
+    if (can_write_without_lock) {
+        sc_bytebuf_commit_write(&ap->buf, size);
+    } else {
+        sc_bytebuf_write(&ap->buf, data, size);
+    }
+
+    // The next time, it will remain at least the current empty space
+    ap->safe_empty_buffer = sc_bytebuf_write_remaining(&ap->buf);
+    SDL_UnlockAudioDevice(ap->device);
+
+    return true;
+}
+
+bool
+sc_audio_player_init(struct sc_audio_player *ap,
+                     const struct sc_audio_player_callbacks *cbs,
+                     void *cbs_userdata) {
+    bool ok = sc_bytebuf_init(&ap->buf, 128 * 1024);
+    if (!ok) {
+        return false;
+    }
+
+    ap->safe_empty_buffer = sc_bytebuf_write_remaining(&ap->buf);
+
+    assert(cbs && cbs->on_ended);
+    ap->cbs = cbs;
+    ap->cbs_userdata = cbs_userdata;
+
+    static const struct sc_frame_sink_ops ops = {
+        .open = sc_audio_player_frame_sink_open,
+        .close = sc_audio_player_frame_sink_close,
+        .push = sc_audio_player_frame_sink_push,
+    };
+
+    ap->frame_sink.ops = &ops;
+    return true;
+}
+
+void
+sc_audio_player_destroy(struct sc_audio_player *ap) {
+    sc_bytebuf_destroy(&ap->buf);
+}

app/src/audio_player.h

@@ -0,0 +1,40 @@
+#ifndef SC_AUDIO_PLAYER_H
+#define SC_AUDIO_PLAYER_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include "trait/frame_sink.h"
+#include <util/bytebuf.h>
+#include <util/thread.h>
+
+#include <libavformat/avformat.h>
+#include <SDL2/SDL.h>
+
+struct sc_audio_player {
+    struct sc_frame_sink frame_sink;
+
+    SDL_AudioDeviceID device;
+
+    // protected by SDL_AudioDeviceLock()
+    struct sc_bytebuf buf;
+    // Number of bytes which could be written without locking
+    size_t safe_empty_buffer;
+
+    const struct sc_audio_player_callbacks *cbs;
+    void *cbs_userdata;
+};
+
+struct sc_audio_player_callbacks {
+    void (*on_ended)(struct sc_audio_player *ap, bool success, void *userdata);
+};
+
+bool
+sc_audio_player_init(struct sc_audio_player *ap,
+                     const struct sc_audio_player_callbacks *cbs,
+                     void *cbs_userdata);
+
+void
+sc_audio_player_destroy(struct sc_audio_player *ap);
+
+#endif

app/src/decoder.c

@@ -25,10 +25,10 @@ sc_decoder_close_sinks(struct sc_decoder *decoder) {
 }
 
 static bool
-sc_decoder_open_sinks(struct sc_decoder *decoder) {
+sc_decoder_open_sinks(struct sc_decoder *decoder, const AVCodecContext *ctx) {
     for (unsigned i = 0; i < decoder->sink_count; ++i) {
         struct sc_frame_sink *sink = decoder->sinks[i];
-        if (!sink->ops->open(sink)) {
+        if (!sink->ops->open(sink, ctx)) {
             sc_decoder_close_first_sinks(decoder, i);
             return false;
         }
@@ -47,6 +47,11 @@ sc_decoder_open(struct sc_decoder *decoder, const AVCodec *codec) {
 
     decoder->codec_ctx->flags |= AV_CODEC_FLAG_LOW_DELAY;
 
+    if (codec->type == AVMEDIA_TYPE_VIDEO) {
+        // Only YUV 4:2:0 is supported, hardcode it
+        decoder->codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
+    }
+
     if (avcodec_open2(decoder->codec_ctx, codec, NULL) < 0) {
         LOGE("Decoder '%s': could not open codec", decoder->name);
         avcodec_free_context(&decoder->codec_ctx);
@@ -61,7 +66,7 @@ sc_decoder_open(struct sc_decoder *decoder, const AVCodec *codec) {
         return false;
     }
 
-    if (!sc_decoder_open_sinks(decoder)) {
+    if (!sc_decoder_open_sinks(decoder, decoder->codec_ctx)) {
         av_frame_free(&decoder->frame);
         avcodec_close(decoder->codec_ctx);
         avcodec_free_context(&decoder->codec_ctx);

app/src/scrcpy.c

@@ -13,6 +13,7 @@
 # include <windows.h>
 #endif
 
+#include "audio_player.h"
 #include "controller.h"
 #include "decoder.h"
 #include "demuxer.h"
@@ -40,6 +41,7 @@
 struct scrcpy {
     struct sc_server server;
     struct sc_screen screen;
+    struct sc_audio_player audio_player;
     struct sc_demuxer video_demuxer;
     struct sc_demuxer audio_demuxer;
     struct sc_decoder video_decoder;
@@ -215,6 +217,17 @@ sc_recorder_on_ended(struct sc_recorder *recorder, bool success,
     }
 }
 
+static void
+sc_audio_player_on_ended(struct sc_audio_player *ap, bool success,
+                         void *userdata) {
+    (void) ap;
+    (void) userdata;
+
+    if (!success) {
+        // TODO
+    }
+}
+
 static void
 sc_video_demuxer_on_ended(struct sc_demuxer *demuxer, bool eos,
                           void *userdata) {
@@ -301,6 +314,7 @@ scrcpy(struct scrcpy_options *options) {
     bool file_pusher_initialized = false;
     bool recorder_initialized = false;
     bool recorder_started = false;
+    bool audio_player_initialized = false;
 #ifdef HAVE_V4L2
     bool v4l2_sink_initialized = false;
 #endif
@@ -383,9 +397,16 @@ scrcpy(struct scrcpy_options *options) {
     }
 
     // Initialize SDL video in addition if display is enabled
-    if (options->display && SDL_Init(SDL_INIT_VIDEO)) {
-        LOGE("Could not initialize SDL: %s", SDL_GetError());
-        goto end;
+    if (options->display) {
+        if (SDL_Init(SDL_INIT_VIDEO)) {
+            LOGE("Could not initialize SDL video: %s", SDL_GetError());
+            goto end;
+        }
+
+        if (options->audio && SDL_Init(SDL_INIT_AUDIO)) {
+            LOGE("Could not initialize SDL audio: %s", SDL_GetError());
+            goto end;
+        }
     }
 
     sdl_configure(options->display, options->disable_screensaver);
@@ -663,6 +684,19 @@ aoa_hid_end:
         screen_initialized = true;
 
         sc_decoder_add_sink(&s->video_decoder, &s->screen.frame_sink);
+
+        if (options->audio) {
+            static const struct sc_audio_player_callbacks audio_player_cbs = {
+                .on_ended = sc_audio_player_on_ended,
+            };
+            if (!sc_audio_player_init(&s->audio_player,
+                                      &audio_player_cbs, NULL)) {
+                goto end;
+            }
+            audio_player_initialized = true;
+
+            sc_decoder_add_sink(&s->audio_decoder, &s->audio_player.frame_sink);
+        }
     }
 
 #ifdef HAVE_V4L2
@@ -783,6 +817,10 @@ end:
         sc_recorder_destroy(&s->recorder);
     }
 
+    if (audio_player_initialized) {
+        sc_audio_player_destroy(&s->audio_player);
+    }
+
     if (file_pusher_initialized) {
         sc_file_pusher_join(&s->file_pusher);
         sc_file_pusher_destroy(&s->file_pusher);

app/src/screen.c

@@ -330,7 +330,10 @@ event_watcher(void *data, SDL_Event *event) {
 #endif
 
 static bool
-sc_screen_frame_sink_open(struct sc_frame_sink *sink) {
+sc_screen_frame_sink_open(struct sc_frame_sink *sink,
+                          const AVCodecContext *ctx) {
+    assert(ctx->pix_fmt == AV_PIX_FMT_YUV420P);
+
     struct sc_screen *screen = DOWNCAST(sink);
     (void) screen;
 #ifndef NDEBUG

app/src/trait/frame_sink.h

@@ -5,6 +5,7 @@
 
 #include <assert.h>
 #include <stdbool.h>
+#include <libavcodec/avcodec.h>
 
 typedef struct AVFrame AVFrame;
 
@@ -18,7 +19,7 @@ struct sc_frame_sink {
 };
 
 struct sc_frame_sink_ops {
-    bool (*open)(struct sc_frame_sink *sink);
+    bool (*open)(struct sc_frame_sink *sink, const AVCodecContext *ctx);
     void (*close)(struct sc_frame_sink *sink);
     bool (*push)(struct sc_frame_sink *sink, const AVFrame *frame);
 };

app/src/util/bytebuf.c

@@ -0,0 +1,114 @@
+#include "bytebuf.h"
+
+#include <assert.h>
+
+#include "util/log.h"
+
+bool
+sc_bytebuf_init(struct sc_bytebuf *buf, size_t alloc_size) {
+    assert(alloc_size);
+    // sufficient, but use more for alignment.
+    buf->data = malloc(alloc_size);
+    if (!buf->data) {
+        LOG_OOM();
+        return false;
+    }
+
+    buf->alloc_size = alloc_size;
+    buf->head = 0;
+    buf->tail = 0;
+
+    return true;
+}
+
+void
+sc_bytebuf_destroy(struct sc_bytebuf *buf) {
+    free(buf->data);
+}
+
+void
+sc_bytebuf_read(struct sc_bytebuf *buf, uint8_t *to, size_t len) {
+    assert(len);
+    assert(sc_bytebuf_read_remaining(buf) >= len);
+    assert(buf->tail != buf->head); // the buffer could not be empty
+
+    size_t right_limit = buf->tail < buf->head ? buf->head : buf->alloc_size;
+    size_t right_len = right_limit - buf->tail;
+    if (len < right_len) {
+        right_len = len;
+    }
+    memcpy(to, buf->data + buf->tail, right_len);
+
+    if (len > right_len) {
+        memcpy(to + right_len, buf->data, len - right_len);
+    }
+
+    buf->tail = (buf->tail + len) % buf->alloc_size;
+}
+
+void
+sc_bytebuf_skip(struct sc_bytebuf *buf, size_t len) {
+    assert(len);
+    assert(sc_bytebuf_read_remaining(buf) >= len);
+    assert(buf->tail != buf->head); // the buffer could not be empty
+
+    buf->tail = (buf->tail + len) % buf->alloc_size;
+}
+
+void
+sc_bytebuf_write(struct sc_bytebuf *buf, const uint8_t *from, size_t len) {
+    assert(len);
+
+    size_t max_len = buf->alloc_size - 1;
+    if (len >= max_len) {
+        // Copy only the right-most bytes
+        memcpy(buf->data, from + len - max_len, max_len);
+        buf->tail = 0;
+        buf->head = max_len;
+        return;
+    }
+
+    size_t right_limit = buf->head < buf->tail ? buf->tail : buf->alloc_size;
+    size_t right_len = right_limit - buf->head;
+    if (len < right_len) {
+        right_len = len;
+    }
+    memcpy(buf->data + buf->head, from, right_len);
+    if (len > right_len) {
+        memcpy(buf->data, from + right_len, len - right_len);
+    }
+
+    size_t empty_space = sc_bytebuf_write_remaining(buf);
+    if (len > empty_space) {
+        buf->tail = (buf->tail + len - empty_space) % buf->alloc_size;
+    }
+    buf->head = (buf->head + len) % buf->alloc_size;
+}
+
+void
+sc_bytebuf_prepare_write(struct sc_bytebuf *buf, const uint8_t *from,
+                         size_t len) {
+    // *This function MUST NOT access buf->tail (even in assert()).*
+    // The purpose of this function is to allow a reader and a writer to access
+    // different parts of the buffer in parallel simultaneously. It is intended
+    // to be called without lock (only sc_bytebuf_commit_write() is intended to
+    // be called with lock held).
+
+    assert(len < buf->alloc_size - 1);
+
+    size_t right_len = buf->alloc_size - buf->head;
+    if (len < right_len) {
+        right_len = len;
+    }
+
+    memcpy(buf->data + buf->head, from, right_len);
+    if (len > right_len) {
+        memcpy(buf->data, from + right_len, len - right_len);
+    }
+}
+
+void
+sc_bytebuf_commit_write(struct sc_bytebuf *buf, size_t len) {
+    assert(len <= sc_bytebuf_write_remaining(buf));
+    buf->head = (buf->head + len) % buf->alloc_size;
+}

app/src/util/bytebuf.h

@@ -0,0 +1,104 @@
+#ifndef SC_BYTEBUF_H
+#define SC_BYTEBUF_H
+
+#include "common.h"
+
+#include <stdbool.h>
+#include <stdint.h>
+
+struct sc_bytebuf {
+    uint8_t *data;
+    // The actual capacity is (allocated - 1) so that head == tail is
+    // non-ambiguous
+    size_t alloc_size;
+    size_t head;
+    size_t tail;
+    // empty: tail == head
+    // full: (tail + 1) % allocated == head
+};
+
+bool
+sc_bytebuf_init(struct sc_bytebuf *buf, size_t alloc_size);
+
+/**
+ * Copy from the bytebuf to a user-provided array
+ *
+ * The caller must check that len <= buf->len (it is an error to attempt to read
+ * more bytes than available).
+ *
+ * This function is guaranteed to not change the head.
+ */
+void
+sc_bytebuf_read(struct sc_bytebuf *buf, uint8_t *to, size_t len);
+
+/**
+ * Drop len bytes from the buffer
+ *
+ * The caller must check that len <= buf->len (it is an error to attempt to skip
+ * more bytes than available).
+ *
+ * This function is guaranteed to not change the head.
+ *
+ * It is equivalent to call sc_bytebuf_read() to some array and discard the
+ * array (but more efficient since there is no copy).
+ */
+void
+sc_bytebuf_skip(struct sc_bytebuf *buf, size_t len);
+
+/**
+ * Copy the user-provided array to the bytebuf
+ *
+ * The length of the input array is not restricted:
+ * if len >= sc_bytebuf_write_remaining(buf), then the excessive input bytes
+ * will overwrite the oldest bytes in the buffer.
+ */
+void
+sc_bytebuf_write(struct sc_bytebuf *buf, const uint8_t *from, size_t len);
+
+/**
+ * Copy the user-provided array to the bytebuf, but do not advance the cursor
+ *
+ * The caller must check that len <= buf->len (it is an error to attempt to
+ * write more bytes than available).
+ *
+ * After this function is called, the write must be committed with
+ * sc_bytebuf_commit_write().
+ *
+ * The purpose of this mechanism is to acquire a lock only to commit the write,
+ * but not to perform the actual copy.
+ */
+void
+sc_bytebuf_prepare_write(struct sc_bytebuf *buf, const uint8_t *from,
+                         size_t len);
+
+/**
+ * Commit a prepared write
+ */
+void
+sc_bytebuf_commit_write(struct sc_bytebuf *buf, size_t len);
+
+/**
+ * Return the number of bytes which can be read
+ *
+ * It is an error to read more bytes than available.
+ */
+static inline size_t
+sc_bytebuf_read_remaining(struct sc_bytebuf *buf) {
+    return (buf->alloc_size + buf->head - buf->tail) % buf->alloc_size;
+}
+
+/**
+ * Return the number of bytes which can be written without overwriting
+ *
+ * It is not an error to write more bytes than the available space, but this
+ * would overwrite the oldest bytes in the buffer.
+ */
+static inline size_t
+sc_bytebuf_write_remaining(struct sc_bytebuf *buf) {
+    return (buf->alloc_size + buf->tail - buf->head - 1) % buf->alloc_size;
+}
+
+void
+sc_bytebuf_destroy(struct sc_bytebuf *buf);
+
+#endif

app/src/v4l2_sink.c

@@ -156,7 +156,9 @@ sc_video_buffer_on_new_frame(struct sc_video_buffer *vb, bool previous_skipped,
 }
 
 static bool
-sc_v4l2_sink_open(struct sc_v4l2_sink *vs) {
+sc_v4l2_sink_open(struct sc_v4l2_sink *vs, const AVCodecContext *ctx) {
+    assert(ctx->pix_fmt == AV_PIX_FMT_YUV420P);
+
     static const struct sc_video_buffer_callbacks cbs = {
         .on_new_frame = sc_video_buffer_on_new_frame,
     };

app/tests/test_bytebuf.c

@@ -0,0 +1,154 @@
+#include "common.h"
+
+#include <assert.h>
+#include <string.h>
+
+#include "util/bytebuf.h"
+
+void test_bytebuf_simple(void) {
+    struct sc_bytebuf buf;
+    uint8_t data[20];
+
+    bool ok = sc_bytebuf_init(&buf, 20);
+    assert(ok);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello", sizeof("hello") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 5);
+
+    sc_bytebuf_read(&buf, data, 4);
+    assert(!strncmp((char *) data, "hell", 4));
+
+    sc_bytebuf_write(&buf, (uint8_t *) " world", sizeof(" world") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 7);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "!", 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 8);
+
+    sc_bytebuf_read(&buf, &data[4], 8);
+    assert(sc_bytebuf_read_remaining(&buf) == 0);
+
+    data[12] = '\0';
+    assert(!strcmp((char *) data, "hello world!"));
+    assert(sc_bytebuf_read_remaining(&buf) == 0);
+
+    sc_bytebuf_destroy(&buf);
+}
+
+void test_bytebuf_boundaries(void) {
+    struct sc_bytebuf buf;
+    uint8_t data[20];
+
+    bool ok = sc_bytebuf_init(&buf, 20);
+    assert(ok);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 6);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 12);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 18);
+
+    sc_bytebuf_read(&buf, data, 9);
+    assert(!strncmp((char *) data, "hello hel", 9));
+    assert(sc_bytebuf_read_remaining(&buf) == 9);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "world", sizeof("world") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 14);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "!", 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 15);
+
+    sc_bytebuf_skip(&buf, 3);
+    assert(sc_bytebuf_read_remaining(&buf) == 12);
+
+    sc_bytebuf_read(&buf, data, 12);
+    data[12] = '\0';
+    assert(!strcmp((char *) data, "hello world!"));
+    assert(sc_bytebuf_read_remaining(&buf) == 0);
+
+    sc_bytebuf_destroy(&buf);
+}
+
+void test_bytebuf_overwrite(void) {
+    struct sc_bytebuf buf;
+    uint8_t data[10];
+
+    bool ok = sc_bytebuf_init(&buf, 10); // so actual capacity is 9
+    assert(ok);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 6);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "abcdef", sizeof("abcdef") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 9);
+
+    sc_bytebuf_read(&buf, data, 9);
+    assert(!strncmp((char *) data, "lo abcdef", 9));
+
+    sc_bytebuf_write(&buf, (uint8_t *) "a very big buffer",
+                     sizeof("a very big buffer") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 9);
+
+    sc_bytebuf_read(&buf, data, 9);
+    assert(!strncmp((char *) data, "ig buffer", 9));
+    assert(sc_bytebuf_read_remaining(&buf) == 0);
+
+    sc_bytebuf_destroy(&buf);
+}
+
+void test_bytebuf_two_steps_write(void) {
+    struct sc_bytebuf buf;
+    uint8_t data[20];
+
+    bool ok = sc_bytebuf_init(&buf, 20);
+    assert(ok);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 6);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 12);
+
+    sc_bytebuf_prepare_write(&buf, (uint8_t *) "hello ", sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 12); // write not committed yet
+
+    sc_bytebuf_read(&buf, data, 9);
+    assert(!strncmp((char *) data, "hello hel", 3));
+    assert(sc_bytebuf_read_remaining(&buf) == 3);
+
+    sc_bytebuf_commit_write(&buf, sizeof("hello ") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 9);
+
+    sc_bytebuf_prepare_write(&buf, (uint8_t *) "world", sizeof("world") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 9); // write not committed yet
+
+    sc_bytebuf_commit_write(&buf, sizeof("world") - 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 14);
+
+    sc_bytebuf_write(&buf, (uint8_t *) "!", 1);
+    assert(sc_bytebuf_read_remaining(&buf) == 15);
+
+    sc_bytebuf_skip(&buf, 3);
+    assert(sc_bytebuf_read_remaining(&buf) == 12);
+
+    sc_bytebuf_read(&buf, data, 12);
+    data[12] = '\0';
+    assert(!strcmp((char *) data, "hello world!"));
+    assert(sc_bytebuf_read_remaining(&buf) == 0);
+
+    sc_bytebuf_destroy(&buf);
+}
+
+int main(int argc, char *argv[]) {
+    (void) argc;
+    (void) argv;
+
+    test_bytebuf_simple();
+    test_bytebuf_boundaries();
+    test_bytebuf_overwrite();
+    test_bytebuf_two_steps_write();
+
+    return 0;
+}

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

@@ -40,7 +40,7 @@ public final class AudioEncoder {
     }
 
     private static final int SAMPLE_RATE = 48000;
-    private static final int CHANNELS = 2;
+    private static final int CHANNELS = 1;
 
     private static final int BUFFER_MS = 10; // milliseconds
     private static final int BUFFER_SIZE = SAMPLE_RATE * CHANNELS * BUFFER_MS / 1000;