From 70bf402776ef215b7cf19042a02ce1cc011b2dac Mon Sep 17 00:00:00 2001
From: Jamie Hardt <jamiehardt@me.com>
Date: Sat, 26 Dec 2020 13:52:52 -0800
Subject: [PATCH] Ambisonic format create/write

---
 README.md         |  2 +-
 src/fmt.rs        | 19 +++++++++++++++++--
 src/wavewriter.rs |  6 +++---
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index c3053cc..02eb4b5 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@ This is currently a work-in-progress! However many features presently work:
 | Transparent promotion to RF64/BW64    | ☑️   |     |
 | Unified interface for regular and extended Wave format | ☑️  |  |
 | Channel/speaker map metadata          | ☑️   | ☑️   |
-| Ambisonic B-format metadata           | ☑️   |     |
+| Ambisonic B-format metadata           | ☑️   | ☑️   |
 | EBU Broadcast-WAVE metadata           | ☑️   | ☑️   |
 | Basic iXML/ADM metadata               | ☑️   |     |
 | Enhanced iXML metadata support        |     |     |
diff --git a/src/fmt.rs b/src/fmt.rs
index b5f0d6b..1c1b53b 100644
--- a/src/fmt.rs
+++ b/src/fmt.rs
@@ -1,5 +1,5 @@
 use uuid::Uuid;
-use super::common_format::{CommonFormat, UUID_PCM};
+use super::common_format::{CommonFormat, UUID_PCM,UUID_BFORMAT_PCM};
 
 #[allow(dead_code)]
 
@@ -195,7 +195,22 @@ impl WaveFmt {
 
     /// Create a new integer PCM format for ambisonic b-format.
     pub fn new_pcm_ambisonic(sample_rate: u32, bits_per_sample: u16, channel_count: u16) -> Self {
-        todo!()
+        let container_bits_per_sample = bits_per_sample + (bits_per_sample % 8);
+        let container_bytes_per_sample= container_bits_per_sample / 8;
+
+        WaveFmt {
+            tag : 0xFFFE,
+            channel_count,
+            sample_rate,
+            bytes_per_second: container_bytes_per_sample as u32 * sample_rate * channel_count as u32,
+            block_alignment: container_bytes_per_sample * channel_count,
+            bits_per_sample: container_bits_per_sample,
+            extended_format: Some(WaveFmtExtended {
+                valid_bits_per_sample: bits_per_sample,
+                channel_mask: ChannelMask::DirectOut as u32,
+                type_guid: UUID_BFORMAT_PCM
+            })
+        }
     }
 
     /// Create a new integer PCM format `WaveFmt` with a custom channel bitmap.
diff --git a/src/wavewriter.rs b/src/wavewriter.rs
index 566d179..24724ac 100644
--- a/src/wavewriter.rs
+++ b/src/wavewriter.rs
@@ -191,9 +191,9 @@ impl<W> WaveWriter<W> where W: Write + Seek {
 
     /// Write Broadcast-Wave metadata to the file.
     /// 
-    /// This function will write the metadata chunk immediately; if you have
-    /// already written and closed the audio data the bext chunk will be 
-    /// positioned after it.
+    /// This function will write the metadata chunk immediately to the end of 
+    /// the file; if you have already written and closed the audio data the 
+    /// bext chunk will be positioned after it.
     fn write_broadcast_metadata(self, bext: &Bext) -> Result<Self,Error> {
         let mut b = self.chunk(BEXT_SIG)?;
         b.write_bext(bext)?;