Make the framerate of the fake cards much more precise.

diff --git a/fake_capture.cpp b/fake_capture.cpp
index 479dc6e0fa387744c4cdf300523baa1fa7afeb1d..53d0db896a958303e16300bd153d2ce2cfb3bb35 100644 (file)
--- a/fake_capture.cpp
+++ b/fake_capture.cpp
@@ -8,6 +8,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 #include <unistd.h>
 #include <cstddef>
 
@@ -134,6 +135,22 @@ void FakeCapture::set_audio_input(uint32_t audio_input_id)
        assert(audio_input_id == 0);
 }
 
+namespace {
+
+void add_time(double t, timespec *ts)
+{
+       ts->tv_nsec += lrint(t * 1e9);
+       ts->tv_sec += ts->tv_nsec / 1000000000;
+       ts->tv_nsec %= 1000000000;
+}
+
+bool timespec_less_than(const timespec &a, const timespec &b)
+{
+       return make_pair(a.tv_sec, a.tv_nsec) < make_pair(b.tv_sec, b.tv_nsec);
+}
+
+}  // namespace
+
 void FakeCapture::producer_thread_func()
 {
        uint16_t timecode = 0;
@@ -141,10 +158,36 @@ void FakeCapture::producer_thread_func()
        if (has_dequeue_callbacks) {
                dequeue_init_callback();
        }
+
+       timespec next_frame;
+       clock_gettime(CLOCK_MONOTONIC, &next_frame);
+       add_time(1.0 / FAKE_FPS, &next_frame);
+
        while (!producer_thread_should_quit) {
-               usleep(1000000 / FAKE_FPS);  // Rather approximate frame rate.
+               timespec now;
+               clock_gettime(CLOCK_MONOTONIC, &now);
+
+               if (timespec_less_than(now, next_frame)) {
+                       // Wait until the next frame.
+                       if (clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME,
+                                            &next_frame, nullptr) == -1) {
+                               if (errno == EINTR) continue;  // Re-check the flag and then sleep again.
+                               perror("clock_nanosleep");
+                               exit(1);
+                       }
+               } else {
+                       // We've seemingly missed a frame. If we're more than one second behind,
+                       // reset the timer; otherwise, just keep going.
+                       timespec limit = next_frame;
+                       ++limit.tv_sec;
+                       if (!timespec_less_than(now, limit)) {
+                               fprintf(stderr, "More than one second of missed fake frames; resetting clock.\n");
+                               next_frame = now;
+                       }
+               }
 
-               if (producer_thread_should_quit) break;
+               // Figure out when the next frame is to be, then compute the current one.
+               add_time(1.0 / FAKE_FPS, &next_frame);
 
                VideoFormat video_format;
                video_format.width = WIDTH;