audio_decoder_test_lib/
sbc.rs

1// Copyright 2020 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use anyhow::{format_err, Result};
6use bitfield::bitfield;
7use fidl_fuchsia_media::*;
8use std::path::Path;
9use std::{fs, io};
10use stream_processor_test::*;
11
12/// Represents an SBC elementary stream.
13pub struct SbcStream {
14    data: Vec<u8>,
15    oob_bytes: Vec<u8>,
16    chunk_frames: usize,
17}
18
19impl SbcStream {
20    /// Constructs an SBC elementary stream from a file with raw elementary stream data.
21    pub fn from_file(
22        filename: impl AsRef<Path>,
23        codec_info: &[u8],
24        chunk_frames: usize,
25    ) -> io::Result<Self> {
26        Ok(SbcStream { data: fs::read(filename)?, oob_bytes: codec_info.to_vec(), chunk_frames })
27    }
28
29    /// Returns an iterator over SBC frames that does not copy.
30    fn frame_iter(&self) -> impl Iterator<Item = SbcFrame<'_>> {
31        SbcFrameIter { data: &self.data, pos: 0, chunk_frames: self.chunk_frames }
32    }
33}
34
35impl ElementaryStream for SbcStream {
36    fn format_details(&self, version_ordinal: u64) -> FormatDetails {
37        FormatDetails {
38            format_details_version_ordinal: Some(version_ordinal),
39            mime_type: Some(String::from("audio/sbc")),
40            oob_bytes: Some(self.oob_bytes.clone()),
41            ..Default::default()
42        }
43    }
44
45    fn is_access_units(&self) -> bool {
46        false
47    }
48
49    fn stream<'a>(&'a self) -> Box<dyn Iterator<Item = ElementaryStreamChunk> + 'a> {
50        Box::new(self.frame_iter().map(|frame| ElementaryStreamChunk {
51            start_access_unit: false,
52            known_end_access_unit: false,
53            data: frame.data.to_vec(),
54            significance: Significance::Audio(AudioSignificance::Encoded),
55            timestamp: None,
56        }))
57    }
58}
59
60#[derive(Debug, PartialEq)]
61enum ChannelMode {
62    Mono,
63    DualChannel,
64    Stereo,
65    JointStereo,
66}
67
68impl From<u8> for ChannelMode {
69    fn from(bits: u8) -> Self {
70        match bits {
71            0 => ChannelMode::Mono,
72            1 => ChannelMode::DualChannel,
73            2 => ChannelMode::Stereo,
74            3 => ChannelMode::JointStereo,
75            _ => panic!("invalid channel mode"),
76        }
77    }
78}
79
80bitfield! {
81    pub struct SbcFrameHeader(u32);
82    impl Debug;
83    u8;
84    syncword, _: 7, 0;
85    subbands, _: 8;
86    allocation_method, _: 9;
87    into ChannelMode, channel_mode, _: 11, 10;
88    blocks_bits, _: 13, 12;
89    sampling_frequency_bits, _: 15, 14;
90    bitpool_bits, _: 23, 16;
91    crc_check, _: 31, 24;
92}
93
94impl SbcFrameHeader {
95    /// The number of channels, based on the channel mode in the header.
96    /// From Table 12.18 in the A2DP Spec.
97    fn channels(&self) -> usize {
98        match self.channel_mode() {
99            ChannelMode::Mono => 1,
100            _ => 2,
101        }
102    }
103
104    fn has_syncword(&self) -> bool {
105        const SBC_SYNCWORD: u8 = 0x9c;
106        self.syncword() == SBC_SYNCWORD
107    }
108
109    /// The number of blocks, based on tbe bits in the header.
110    /// From Table 12.17 in the A2DP Spec.
111    fn blocks(&self) -> usize {
112        4 * (self.blocks_bits() + 1) as usize
113    }
114
115    fn bitpool(&self) -> usize {
116        self.bitpool_bits() as usize
117    }
118
119    /// Number of subbands based on the header bit.
120    /// From Table 12.20 in the A2DP Spec.
121    fn num_subbands(&self) -> usize {
122        if self.subbands() {
123            8
124        } else {
125            4
126        }
127    }
128
129    /// Calculates the frame length.
130    /// Formula from Section 12.9 of the A2DP Spec.
131    fn frame_length(&self) -> Result<usize> {
132        if !self.has_syncword() {
133            return Err(format_err!("syncword does not match"));
134        }
135        let len = 4 + (4 * self.num_subbands() * self.channels()) / 8;
136        let rest = (match self.channel_mode() {
137            ChannelMode::Mono | ChannelMode::DualChannel => {
138                self.blocks() * self.channels() * self.bitpool()
139            }
140            ChannelMode::Stereo => self.blocks() * self.bitpool(),
141            ChannelMode::JointStereo => self.num_subbands() + (self.blocks() * self.bitpool()),
142        } as f64
143            / 8.0)
144            .ceil() as usize;
145        Ok(len + rest)
146    }
147
148    /// Given a buffer with an SBC frame at the start, find the length of the
149    /// SBC frame.
150    fn find_sbc_frame_len(buf: &[u8]) -> Result<usize> {
151        if buf.len() < 4 {
152            return Err(format_err!("Buffer too short for header"));
153        }
154        let hdr = u32::from_le_bytes((&buf[0..4]).try_into()?);
155        SbcFrameHeader(hdr).frame_length()
156    }
157}
158
159pub struct SbcFrame<'a> {
160    pub data: &'a [u8],
161    pub length: usize,
162}
163
164/// An iterator over frames in an SBC stream.
165struct SbcFrameIter<'a> {
166    data: &'a [u8],
167    pos: usize,
168    chunk_frames: usize,
169}
170
171impl<'a> SbcFrameIter<'a> {
172    fn next_frame(&self, pos: usize) -> Option<SbcFrame<'a>> {
173        SbcFrameHeader::find_sbc_frame_len(&self.data[pos..])
174            .map(|len| {
175                let end_pos = std::cmp::min(pos + len * self.chunk_frames, self.data.len());
176                let frame_len = end_pos - pos;
177                SbcFrame { data: &self.data[pos..end_pos], length: frame_len }
178            })
179            .ok()
180    }
181}
182
183impl<'a> Iterator for SbcFrameIter<'a> {
184    type Item = SbcFrame<'a>;
185    fn next(&mut self) -> Option<Self::Item> {
186        if self.pos >= self.data.len() {
187            return None;
188        }
189        let frame = self.next_frame(self.pos);
190        self.pos += frame.as_ref().map(|f| f.length).unwrap_or(0);
191        frame
192    }
193}
audio_decoder_test_lib/sbc.rs

audio_decoder_test_lib/
sbc.rs
