+ if (output_card_index != -1) {
+ // The output card (ie., cards[output_card_index].output) is the master clock,
+ // so no input card (ie., cards[card_index].capture) is.
+ return false;
+ }
+ return (card_index == master_card_index);
+}
+
+void Mixer::trim_queue(CaptureCard *card, unsigned card_index)
+{
+ // Count the number of frames in the queue, including any frames
+ // we dropped. It's hard to know exactly how we should deal with
+ // dropped (corrupted) input frames; they don't help our goal of
+ // avoiding starvation, but they still add to the problem of latency.
+ // Since dropped frames is going to mean a bump in the signal anyway,
+ // we err on the side of having more stable latency instead.
+ unsigned queue_length = 0;
+ for (const CaptureCard::NewFrame &frame : card->new_frames) {
+ queue_length += frame.dropped_frames + 1;
+ }
+ card->queue_length_policy.update_policy(queue_length);
+
+ // If needed, drop frames until the queue is below the safe limit.
+ // We prefer to drop from the head, because all else being equal,
+ // we'd like more recent frames (less latency).
+ unsigned dropped_frames = 0;
+ while (queue_length > card->queue_length_policy.get_safe_queue_length()) {
+ assert(!card->new_frames.empty());
+ assert(queue_length > card->new_frames.front().dropped_frames);
+ queue_length -= card->new_frames.front().dropped_frames;
+
+ if (queue_length <= card->queue_length_policy.get_safe_queue_length()) {
+ // No need to drop anything.
+ break;
+ }
+
+ card->new_frames.pop_front();
+ card->new_frames_changed.notify_all();
+ --queue_length;
+ ++dropped_frames;
+ }
+
+ if (dropped_frames > 0) {
+ fprintf(stderr, "Card %u dropped %u frame(s) to keep latency down.\n",
+ card_index, dropped_frames);
+ }
+}
+
+
+Mixer::OutputFrameInfo Mixer::get_one_frame_from_each_card(unsigned master_card_index, bool master_card_is_output, CaptureCard::NewFrame new_frames[MAX_VIDEO_CARDS], bool has_new_frame[MAX_VIDEO_CARDS])
+{
+ OutputFrameInfo output_frame_info;
+start:
+ unique_lock<mutex> lock(card_mutex, defer_lock);
+ if (master_card_is_output) {
+ // Clocked to the output, so wait for it to be ready for the next frame.
+ cards[master_card_index].output->wait_for_frame(pts_int, &output_frame_info.dropped_frames, &output_frame_info.frame_duration, &output_frame_info.is_preroll, &output_frame_info.frame_timestamp);
+ lock.lock();
+ } else {
+ // Wait for the master card to have a new frame.
+ // TODO: Add a timeout.
+ output_frame_info.is_preroll = false;
+ lock.lock();
+ cards[master_card_index].new_frames_changed.wait(lock, [this, master_card_index]{ return !cards[master_card_index].new_frames.empty() || cards[master_card_index].capture->get_disconnected(); });
+ }
+
+ if (master_card_is_output) {
+ handle_hotplugged_cards();
+ } else if (cards[master_card_index].new_frames.empty()) {
+ // We were woken up, but not due to a new frame. Deal with it
+ // and then restart.
+ assert(cards[master_card_index].capture->get_disconnected());
+ handle_hotplugged_cards();
+ goto start;
+ }
+
+ if (!master_card_is_output) {
+ output_frame_info.frame_timestamp =
+ cards[master_card_index].new_frames.front().received_timestamp;
+ }
+
+ for (unsigned card_index = 0; card_index < num_cards; ++card_index) {
+ CaptureCard *card = &cards[card_index];
+ if (input_card_is_master_clock(card_index, master_card_index)) {
+ // We don't use the queue length policy for the master card,
+ // but we will if it stops being the master. Thus, clear out
+ // the policy in case we switch in the future.
+ card->queue_length_policy.reset(card_index);
+ assert(!card->new_frames.empty());
+ } else {
+ trim_queue(card, card_index);
+ }
+ if (!card->new_frames.empty()) {
+ new_frames[card_index] = move(card->new_frames.front());
+ has_new_frame[card_index] = true;
+ card->new_frames.pop_front();
+ card->new_frames_changed.notify_all();
+ }
+ }
+
+ if (!master_card_is_output) {
+ output_frame_info.dropped_frames = new_frames[master_card_index].dropped_frames;
+ output_frame_info.frame_duration = new_frames[master_card_index].length;
+ }
+
+ // This might get off by a fractional sample when changing master card
+ // between ones with different frame rates, but that's fine.
+ int num_samples_times_timebase = OUTPUT_FREQUENCY * output_frame_info.frame_duration + fractional_samples;
+ output_frame_info.num_samples = num_samples_times_timebase / TIMEBASE;
+ fractional_samples = num_samples_times_timebase % TIMEBASE;
+ assert(output_frame_info.num_samples >= 0);
+
+ return output_frame_info;
+}
+
+void Mixer::handle_hotplugged_cards()
+{
+ // Check for cards that have been disconnected since last frame.
+ for (unsigned card_index = 0; card_index < num_cards; ++card_index) {
+ CaptureCard *card = &cards[card_index];
+ if (card->capture->get_disconnected()) {
+ fprintf(stderr, "Card %u went away, replacing with a fake card.\n", card_index);
+ FakeCapture *capture = new FakeCapture(global_flags.width, global_flags.height, FAKE_FPS, OUTPUT_FREQUENCY, card_index, global_flags.fake_cards_audio);
+ configure_card(card_index, capture, /*is_fake_capture=*/true, /*output=*/nullptr);
+ card->queue_length_policy.reset(card_index);
+ card->capture->start_bm_capture();
+ }
+ }
+
+ // Check for cards that have been connected since last frame.
+ vector<libusb_device *> hotplugged_cards_copy;
+ {
+ lock_guard<mutex> lock(hotplug_mutex);
+ swap(hotplugged_cards, hotplugged_cards_copy);
+ }
+ for (libusb_device *new_dev : hotplugged_cards_copy) {
+ // Look for a fake capture card where we can stick this in.
+ int free_card_index = -1;
+ for (unsigned card_index = 0; card_index < num_cards; ++card_index) {
+ if (cards[card_index].is_fake_capture) {
+ free_card_index = card_index;
+ break;
+ }
+ }
+
+ if (free_card_index == -1) {
+ fprintf(stderr, "New card plugged in, but no free slots -- ignoring.\n");
+ libusb_unref_device(new_dev);
+ } else {
+ // BMUSBCapture takes ownership.
+ fprintf(stderr, "New card plugged in, choosing slot %d.\n", free_card_index);
+ CaptureCard *card = &cards[free_card_index];
+ BMUSBCapture *capture = new BMUSBCapture(free_card_index, new_dev);
+ configure_card(free_card_index, capture, /*is_fake_capture=*/false, /*output=*/nullptr);
+ card->queue_length_policy.reset(free_card_index);
+ capture->set_card_disconnected_callback(bind(&Mixer::bm_hotplug_remove, this, free_card_index));
+ capture->start_bm_capture();
+ }
+ }
+}
+
+
+void Mixer::schedule_audio_resampling_tasks(unsigned dropped_frames, int num_samples_per_frame, int length_per_frame, bool is_preroll, steady_clock::time_point frame_timestamp)
+{
+ // Resample the audio as needed, including from previously dropped frames.
+ assert(num_cards > 0);
+ for (unsigned frame_num = 0; frame_num < dropped_frames + 1; ++frame_num) {
+ const bool dropped_frame = (frame_num != dropped_frames);
+ {
+ // Signal to the audio thread to process this frame.
+ // Note that if the frame is a dropped frame, we signal that
+ // we don't want to use this frame as base for adjusting
+ // the resampler rate. The reason for this is that the timing
+ // of these frames is often way too late; they typically don't
+ // “arrive” before we synthesize them. Thus, we could end up
+ // in a situation where we have inserted e.g. five audio frames
+ // into the queue before we then start pulling five of them
+ // back out. This makes ResamplingQueue overestimate the delay,
+ // causing undue resampler changes. (We _do_ use the last,
+ // non-dropped frame; perhaps we should just discard that as well,
+ // since dropped frames are expected to be rare, and it might be
+ // better to just wait until we have a slightly more normal situation).
+ unique_lock<mutex> lock(audio_mutex);
+ bool adjust_rate = !dropped_frame && !is_preroll;
+ audio_task_queue.push(AudioTask{pts_int, num_samples_per_frame, adjust_rate, frame_timestamp});
+ audio_task_queue_changed.notify_one();
+ }
+ if (dropped_frame) {
+ // For dropped frames, increase the pts. Note that if the format changed
+ // in the meantime, we have no way of detecting that; we just have to
+ // assume the frame length is always the same.
+ pts_int += length_per_frame;
+ }
+ }
+}
+
+void Mixer::render_one_frame(int64_t duration)
+{
+ // Determine the time code for this frame before we start rendering.
+ string timecode_text = timecode_renderer->get_timecode_text(double(pts_int) / TIMEBASE, frame_num);
+ if (display_timecode_on_stdout) {
+ printf("Timecode: '%s'\n", timecode_text.c_str());
+ }
+