From 8b4a8b1610810c50ac7afe68577cd86cf04b2b06 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Sat, 29 Apr 2017 01:27:33 +0200
Subject: [PATCH] Support other sample rates than 48 kHz.

---
 bmusb.cpp     | 27 +++++++++++++++++++++++++++
 bmusb/bmusb.h |  1 +
 2 files changed, 28 insertions(+)

diff --git a/bmusb.cpp b/bmusb.cpp
index ed6fa26..663a235 100644
--- a/bmusb.cpp
+++ b/bmusb.cpp
@@ -241,6 +241,26 @@ bool decode_video_format(uint16_t video_format, VideoFormat *decoded_video_forma
 	return false;
 }
 
+// There are seemingly no direct indicators of sample rate; you just get
+// one frame's worth and have to guess from that.
+int guess_sample_rate(const VideoFormat &video_format, size_t len)
+{
+	size_t num_samples = len / 3 / 8;
+	size_t num_samples_per_second = num_samples * video_format.frame_rate_nom / video_format.frame_rate_den;
+
+	// See if we match or are very close to any of the mandatory HDMI sample rates.
+	const int candidate_sample_rates[] = { 32000, 44100, 48000 };
+	for (int rate : candidate_sample_rates) {
+		if (abs(int(num_samples_per_second) - rate) < 50) {
+			return rate;
+		}
+	}
+
+	fprintf(stderr, "%ld samples at %d/%d fps (%ld Hz) matches no known sample rate, assuming 48000 Hz\n",
+		num_samples, video_format.frame_rate_nom, video_format.frame_rate_den, num_samples_per_second);
+	return 48000;
+}
+
 }  // namespace
 
 FrameAllocator::~FrameAllocator() {}
@@ -332,6 +352,7 @@ void BMUSBCapture::dequeue_thread_func()
 	if (has_dequeue_callbacks) {
 		dequeue_init_callback();
 	}
+	size_t last_sample_rate = 48000;
 	while (!dequeue_thread_should_quit) {
 		unique_lock<mutex> lock(queue_lock);
 		queues_not_empty.wait(lock, [this]{ return dequeue_thread_should_quit || (!pending_video_frames.empty() && !pending_audio_frames.empty()); });
@@ -343,6 +364,7 @@ void BMUSBCapture::dequeue_thread_func()
 		AudioFormat audio_format;
 		audio_format.bits_per_sample = 24;
 		audio_format.num_channels = 8;
+		audio_format.sample_rate = last_sample_rate;
 		if (uint16_less_than_with_wraparound(video_timecode, audio_timecode)) {
 			printf("Video block 0x%04x without corresponding audio block, dropping.\n",
 				video_timecode);
@@ -383,10 +405,15 @@ void BMUSBCapture::dequeue_thread_func()
 			VideoFormat video_format;
 			audio_format.id = audio_frame.format;
 			if (decode_video_format(video_frame.format, &video_format)) {
+				if (audio_frame.frame.len != 0) {
+					audio_format.sample_rate = guess_sample_rate(video_format, audio_frame.frame.len);
+					last_sample_rate = audio_format.sample_rate;
+				}
 				frame_callback(video_timecode,
 					       video_frame.frame, HEADER_SIZE, video_format,
 					       audio_frame.frame, AUDIO_HEADER_SIZE, audio_format);
 			} else {
+				audio_format.sample_rate = last_sample_rate;
 				frame_callback(video_timecode,
 				               FrameAllocator::Frame(), 0, video_format,
 					       audio_frame.frame, AUDIO_HEADER_SIZE, audio_format);
diff --git a/bmusb/bmusb.h b/bmusb/bmusb.h
index 7a31a4d..6d6f097 100644
--- a/bmusb/bmusb.h
+++ b/bmusb/bmusb.h
@@ -126,6 +126,7 @@ struct AudioFormat {
 	uint16_t id = 0;  // For debugging/logging only.
 	unsigned bits_per_sample = 0;
 	unsigned num_channels = 0;
+	unsigned sample_rate = 48000;
 };
 
 enum PixelFormat {
-- 
2.39.2