Remove option --render-expired-frames

This flag forced the decoder to wait for the previous frame to be
consumed by the display.

It was initially implemented as a compilation flag for testing, not
intended to be exposed at runtime. But to remove ifdefs and to allow
users to test this flag easily, it had finally been exposed by commit
ebccb9f.

In practice, it turned out to be useless: it had no practical impact,
and it did not solve or mitigate any performance issues causing frame
skipping.

But that added some complexity to the codebase: it required an
additional condition variable, and made video buffer calls possibly
blocking, which in turn required code to interrupt it on exit.

To prepare support for multiple sinks plugged to the decoder (display
and v4l2 for example), the blocking call used for pacing the decoder
output becomes unacceptable, so just remove this useless "feature".

README.md

@@ -491,18 +491,6 @@ scrcpy -Sw
 ```
 
 
-#### Render expired frames
-
-By default, to minimize latency, _scrcpy_ always renders the last decoded frame
-available, and drops any previous one.
-
-To force the rendering of all frames (at a cost of a possible increased
-latency), use:
-
-```bash
-scrcpy --render-expired-frames
-```
-
 #### Show touches
 
 For presentations, it may be useful to show physical touches (on the physical

app/scrcpy.1

@@ -155,10 +155,6 @@ Supported names are currently "direct3d", "opengl", "opengles2", "opengles", "me
 .UR https://wiki.libsdl.org/SDL_HINT_RENDER_DRIVER
 .UE
 
-.TP
-.B \-\-render\-expired\-frames
-By default, to minimize latency, scrcpy always renders the last available decoded frame, and drops any previous ones. This flag forces to render all frames, at a cost of a possible increased latency.
-
 .TP
 .BI "\-\-rotation " value
 Set the initial display rotation. Possibles values are 0, 1, 2 and 3. Each increment adds a 90 degrees rotation counterclockwise.

app/src/cli.c

@@ -143,12 +143,6 @@ scrcpy_print_usage(const char *arg0) {
         "        \"opengles2\", \"opengles\", \"metal\" and \"software\".\n"
         "        <https://wiki.libsdl.org/SDL_HINT_RENDER_DRIVER>\n"
         "\n"
-        "    --render-expired-frames\n"
-        "        By default, to minimize latency, scrcpy always renders the\n"
-        "        last available decoded frame, and drops any previous ones.\n"
-        "        This flag forces to render all frames, at a cost of a\n"
-        "        possible increased latency.\n"
-        "\n"
         "    --rotation value\n"
         "        Set the initial display rotation.\n"
         "        Possibles values are 0, 1, 2 and 3. Each increment adds a 90\n"
@@ -816,7 +810,8 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
                 opts->stay_awake = true;
                 break;
             case OPT_RENDER_EXPIRED_FRAMES:
-                opts->render_expired_frames = true;
+                LOGW("Option --render-expired-frames has been removed. This "
+                     "flag has been ignored.");
                 break;
             case OPT_WINDOW_TITLE:
                 opts->window_title = optarg;

app/src/decoder.c

@@ -69,8 +69,3 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
 #endif
     return true;
 }
-
-void
-decoder_interrupt(struct decoder *decoder) {
-    video_buffer_interrupt(decoder->video_buffer);
-}

app/src/decoder.h

@@ -26,7 +26,4 @@ decoder_close(struct decoder *decoder);
 bool
 decoder_push(struct decoder *decoder, const AVPacket *packet);
 
-void
-decoder_interrupt(struct decoder *decoder);
-
 #endif

app/src/scrcpy.c

@@ -334,7 +334,7 @@ scrcpy(const struct scrcpy_options *options) {
         }
         fps_counter_initialized = true;
 
-        if (!video_buffer_init(&video_buffer, options->render_expired_frames)) {
+        if (!video_buffer_init(&video_buffer)) {
             goto end;
         }
         video_buffer_initialized = true;
@@ -430,11 +430,8 @@ scrcpy(const struct scrcpy_options *options) {
     LOGD("quit...");
 
 end:
-    // stop stream and controller so that they don't continue once their socket
-    // is shutdown
-    if (stream_started) {
-        stream_stop(&stream);
-    }
+    // The stream is not stopped explicitly, because it will stop by itself on
+    // end-of-stream
     if (controller_started) {
         controller_stop(&controller);
     }

app/src/scrcpy.h

@@ -72,7 +72,6 @@ struct scrcpy_options {
     bool control;
     bool display;
     bool turn_screen_off;
-    bool render_expired_frames;
     bool prefer_text;
     bool window_borderless;
     bool mipmaps;
@@ -120,7 +119,6 @@ struct scrcpy_options {
     .control = true, \
     .display = true, \
     .turn_screen_off = false, \
-    .render_expired_frames = false, \
     .prefer_text = false, \
     .window_borderless = false, \
     .mipmaps = true, \

app/src/stream.c

@@ -285,13 +285,6 @@ stream_start(struct stream *stream) {
     return true;
 }
 
-void
-stream_stop(struct stream *stream) {
-    if (stream->decoder) {
-        decoder_interrupt(stream->decoder);
-    }
-}
-
 void
 stream_join(struct stream *stream) {
     sc_thread_join(&stream->thread, NULL);

app/src/stream.h

@@ -31,9 +31,6 @@ stream_init(struct stream *stream, socket_t socket,
 bool
 stream_start(struct stream *stream);
 
-void
-stream_stop(struct stream *stream);
-
 void
 stream_join(struct stream *stream);
 

app/src/video_buffer.c

@@ -7,7 +7,7 @@
 #include "util/log.h"
 
 bool
-video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
+video_buffer_init(struct video_buffer *vb) {
     vb->producer_frame = av_frame_alloc();
     if (!vb->producer_frame) {
         goto error_0;
@@ -28,18 +28,6 @@ video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
         goto error_3;
     }
 
-    vb->wait_consumer = wait_consumer;
-    if (wait_consumer) {
-        ok = sc_cond_init(&vb->pending_frame_consumed_cond);
-        if (!ok) {
-            sc_mutex_destroy(&vb->mutex);
-            goto error_2;
-        }
-        // interrupted is not used if wait_consumer is disabled since offering
-        // a frame will never block
-        vb->interrupted = false;
-    }
-
     // there is initially no frame, so consider it has already been consumed
     vb->pending_frame_consumed = true;
 
@@ -61,9 +49,6 @@ video_buffer_init(struct video_buffer *vb, bool wait_consumer) {
 
 void
 video_buffer_destroy(struct video_buffer *vb) {
-    if (vb->wait_consumer) {
-        sc_cond_destroy(&vb->pending_frame_consumed_cond);
-    }
     sc_mutex_destroy(&vb->mutex);
     av_frame_free(&vb->consumer_frame);
     av_frame_free(&vb->pending_frame);
@@ -93,12 +78,6 @@ video_buffer_producer_offer_frame(struct video_buffer *vb) {
     assert(vb->cbs);
 
     sc_mutex_lock(&vb->mutex);
-    if (vb->wait_consumer) {
-        // wait for the current (expired) frame to be consumed
-        while (!vb->pending_frame_consumed && !vb->interrupted) {
-            sc_cond_wait(&vb->pending_frame_consumed_cond, &vb->mutex);
-        }
-    }
 
     av_frame_unref(vb->pending_frame);
     swap_frames(&vb->producer_frame, &vb->pending_frame);
@@ -125,23 +104,8 @@ video_buffer_consumer_take_frame(struct video_buffer *vb) {
     swap_frames(&vb->consumer_frame, &vb->pending_frame);
     av_frame_unref(vb->pending_frame);
 
-    if (vb->wait_consumer) {
-        // unblock video_buffer_offer_decoded_frame()
-        sc_cond_signal(&vb->pending_frame_consumed_cond);
-    }
     sc_mutex_unlock(&vb->mutex);
 
     // consumer_frame is only written from this thread, no need to lock
     return vb->consumer_frame;
 }
-
-void
-video_buffer_interrupt(struct video_buffer *vb) {
-    if (vb->wait_consumer) {
-        sc_mutex_lock(&vb->mutex);
-        vb->interrupted = true;
-        sc_mutex_unlock(&vb->mutex);
-        // wake up blocking wait
-        sc_cond_signal(&vb->pending_frame_consumed_cond);
-    }
-}

app/src/video_buffer.h

@@ -34,10 +34,7 @@ struct video_buffer {
     AVFrame *consumer_frame;
 
     sc_mutex mutex;
-    bool wait_consumer; // never overwrite a pending frame if it is not consumed
-    bool interrupted;
 
-    sc_cond pending_frame_consumed_cond;
     bool pending_frame_consumed;
 
     const struct video_buffer_callbacks *cbs;
@@ -56,7 +53,7 @@ struct video_buffer_callbacks {
 };
 
 bool
-video_buffer_init(struct video_buffer *vb, bool wait_consumer);
+video_buffer_init(struct video_buffer *vb);
 
 void
 video_buffer_destroy(struct video_buffer *vb);
@@ -75,8 +72,4 @@ video_buffer_producer_offer_frame(struct video_buffer *vb);
 const AVFrame *
 video_buffer_consumer_take_frame(struct video_buffer *vb);
 
-// wake up and avoid any blocking call
-void
-video_buffer_interrupt(struct video_buffer *vb);
-
 #endif

app/tests/test_cli.c

@@ -58,7 +58,6 @@ static void test_options(void) {
         "--push-target", "/sdcard/Movies",
         "--record", "file",
         "--record-format", "mkv",
-        "--render-expired-frames",
         "--serial", "0123456789abcdef",
         "--show-touches",
         "--turn-screen-off",
@@ -87,7 +86,6 @@ static void test_options(void) {
     assert(!strcmp(opts->push_target, "/sdcard/Movies"));
     assert(!strcmp(opts->record_filename, "file"));
     assert(opts->record_format == SC_RECORD_FORMAT_MKV);
-    assert(opts->render_expired_frames);
     assert(!strcmp(opts->serial, "0123456789abcdef"));
     assert(opts->show_touches);
     assert(opts->turn_screen_off);