Releax BLACK_THRESHOLD value & optimize wav header initialization

Set BLACK_THRESHOLD to 100 down from 200
Avoid unnecessary wav_hdr copy when initializing it
Update outdated reference to the WAV spec in the wav.h

main.c

@@ -10,7 +10,7 @@
 #include "surface.h"
 
 #define DECODED_SOUND_FILE "vinyl_decoded.wav"
-#define BLACK_THRESHOLD 200
+#define BLACK_THRESHOLD 100
 #define DEGREE_STRIDE 0.1
 #define SCREEN_WIDTH 2000
 #define SCREEN_HEIGHT 2000
@@ -171,7 +171,7 @@ void vinyl_decode(SDL_Window* sdl_window, SDL_Surface* screen_surface, SDL_Surfa
 	}
 
 	// replace placeholder wav_hdr struct in the beginning of file with the actual one
-	hdr = mk_wav_hdr(samples_written);
+	init_wav_hdr(&hdr, samples_written);
 	rewind(decoded_sound);
 	fwrite(&hdr, sizeof(hdr), 1, decoded_sound);
 	fclose(decoded_sound);

wav.c

@@ -1,28 +1,26 @@
 #include <string.h>
 #include "wav.h"
 
+#define CHUNK_ID "RIFF"
+#define FORMAT "WAVE"
+#define SUBCHUNK1_ID "fmt "
+#define SUBCHUNK2_ID "data"
+
 //TODO: determine payload size dynamically
-struct wav_hdr mk_wav_hdr(uint32_t payload_size)
+void init_wav_hdr(struct wav_hdr *hdr, uint32_t payload_size)
 {
-	struct wav_hdr hdr;
-	const char* chunk_id = "RIFF";
-	const char* format = "WAVE";
-	const char* subchunk1_id = "fmt ";
-	const char* subchunk2_id = "data";
-
-	strncpy(hdr.chunk_id, chunk_id, strlen(chunk_id));
-	hdr.chunk_size = 0x6424;
-	strncpy(hdr.format, format, strlen(format));
-	strncpy(hdr.subchunk1_id, subchunk1_id, strlen(subchunk1_id));
-	hdr.subchunk1_size = 0x10;
-	hdr.audio_format = 0x01;
-	hdr.channels = 0x01;
-	hdr.sample_rate = 0x1F40;
-	hdr.byte_rate = 0x1F40;
-	hdr.block_align = 0x01;
-	hdr.bits_per_sample = 0x08;
-	strncpy(hdr.subchunk2_id, subchunk2_id, strlen(subchunk2_id));
-	hdr.subchunk2_size = 0x45A00;
-
-	return hdr;
+	memset(hdr, 0, sizeof(*hdr));
+	strncpy(hdr->chunk_id, CHUNK_ID, strlen(CHUNK_ID));
+	hdr->chunk_size = 0x6424;
+	strncpy(hdr->format, FORMAT, strlen(FORMAT));
+	strncpy(hdr->subchunk1_id, SUBCHUNK1_ID, strlen(SUBCHUNK1_ID));
+	hdr->subchunk1_size = 0x10;
+	hdr->audio_format = 0x01;
+	hdr->channels = 0x01;
+	hdr->sample_rate = 0x1F40;
+	hdr->byte_rate = 0x1F40;
+	hdr->block_align = 0x01;
+	hdr->bits_per_sample = 0x08;
+	strncpy(hdr->subchunk2_id, SUBCHUNK2_ID, strlen(SUBCHUNK2_ID));
+	hdr->subchunk2_size = 0x45A00;
 }

wav.h

@@ -1,6 +1,6 @@
 #include <stdint.h>
 // WAV header
-// https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
+// http://soundfile.sapp.org/doc/WaveFormat/
 struct wav_hdr {
 	char chunk_id[4];
 	uint32_t chunk_size;
@@ -17,4 +17,4 @@ struct wav_hdr {
 	uint32_t subchunk2_size;
 } __attribute__((packed));
 
-struct wav_hdr mk_wav_hdr(uint32_t payload_size);
+void init_wav_hdr(struct wav_hdr *hdr, uint32_t payload_size);