dvb_si/descriptors/
audio_stream.rs

1//! Audio Stream Descriptor — ISO/IEC 13818-1 §2.6.4 (tag 0x03).
2//!
3//! Describes the elementary stream as an MPEG audio stream.
4
5use super::descriptor_body;
6use crate::error::{Error, Result};
7use dvb_common::{Parse, Serialize};
8
9/// Descriptor tag for audio_stream_descriptor.
10pub const TAG: u8 = 0x03;
11const HEADER_LEN: usize = 2;
12const BODY_LEN: u8 = 1;
13
14/// Audio Stream Descriptor.
15#[derive(Debug, Clone, PartialEq, Eq)]
16#[cfg_attr(feature = "serde", derive(serde::Serialize))]
17#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
18pub struct AudioStreamDescriptor {
19    /// Free format flag.
20    pub free_format_flag: bool,
21    /// MPEG audio ID.
22    pub id: bool,
23    /// Layer (0=reserved).
24    pub layer: u8,
25    /// Variable rate audio indicator.
26    pub variable_rate_audio_indicator: bool,
27}
28
29impl<'a> Parse<'a> for AudioStreamDescriptor {
30    type Error = crate::error::Error;
31
32    fn parse(bytes: &'a [u8]) -> Result<Self> {
33        let body = descriptor_body(
34            bytes,
35            TAG,
36            "AudioStreamDescriptor",
37            "unexpected tag for audio_stream_descriptor",
38        )?;
39        if body.len() != BODY_LEN as usize {
40            return Err(Error::InvalidDescriptor {
41                tag: TAG,
42                reason: "audio_stream_descriptor length must equal 1",
43            });
44        }
45        let b = body[0];
46        Ok(Self {
47            free_format_flag: (b & 0x80) != 0,
48            id: (b & 0x40) != 0,
49            layer: (b >> 4) & 0x03,
50            variable_rate_audio_indicator: (b & 0x08) != 0,
51        })
52    }
53}
54
55impl Serialize for AudioStreamDescriptor {
56    type Error = crate::error::Error;
57
58    fn serialized_len(&self) -> usize {
59        HEADER_LEN + (BODY_LEN as usize)
60    }
61
62    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
63        let len = self.serialized_len();
64        if buf.len() < len {
65            return Err(Error::OutputBufferTooSmall {
66                need: len,
67                have: buf.len(),
68            });
69        }
70        buf[0] = TAG;
71        buf[1] = BODY_LEN;
72        buf[HEADER_LEN] = ((self.free_format_flag as u8) << 7)
73            | ((self.id as u8) << 6)
74            | ((self.layer & 0x03) << 4)
75            | ((self.variable_rate_audio_indicator as u8) << 3);
76        Ok(len)
77    }
78}
79impl<'a> crate::traits::DescriptorDef<'a> for AudioStreamDescriptor {
80    const TAG: u8 = TAG;
81    const NAME: &'static str = "AUDIO_STREAM";
82}
83
84#[cfg(test)]
85mod tests {
86    use super::*;
87
88    #[test]
89    fn parse() {
90        let bytes = [
91            TAG,
92            1,
93            0b1110_1000, // free=1, id=1, layer=2, variable=1, reserved=0
94        ];
95        let d = AudioStreamDescriptor::parse(&bytes).unwrap();
96        assert!(d.free_format_flag);
97        assert!(d.id);
98        assert_eq!(d.layer, 2);
99        assert!(d.variable_rate_audio_indicator);
100    }
101
102    #[test]
103    fn serialize_round_trip() {
104        let d = AudioStreamDescriptor {
105            free_format_flag: false,
106            id: true,
107            layer: 3,
108            variable_rate_audio_indicator: false,
109        };
110        let mut buf = vec![0u8; d.serialized_len()];
111        d.serialize_into(&mut buf).unwrap();
112        let reparsed = AudioStreamDescriptor::parse(&buf).unwrap();
113        assert_eq!(d, reparsed);
114    }
115
116    #[test]
117    fn parse_rejects_wrong_length() {
118        let err = AudioStreamDescriptor::parse(&[TAG, 0]).unwrap_err();
119        assert!(matches!(err, Error::InvalidDescriptor { tag: TAG, .. }));
120    }
121
122    #[test]
123    fn parse_rejects_wrong_tag() {
124        let err = AudioStreamDescriptor::parse(&[0x04, 1, 0x00]).unwrap_err();
125        assert!(matches!(err, Error::InvalidDescriptor { tag: 0x04, .. }));
126    }
127
128    #[test]
129    fn serialize_rejects_small_buffer() {
130        let d = AudioStreamDescriptor {
131            free_format_flag: false,
132            id: false,
133            layer: 0,
134            variable_rate_audio_indicator: false,
135        };
136        let mut tiny = vec![0u8; 2];
137        let err = d.serialize_into(&mut tiny).unwrap_err();
138        assert!(matches!(err, Error::OutputBufferTooSmall { .. }));
139    }
140}
dvb_si/descriptors/audio_stream.rs

dvb_si/descriptors/
audio_stream.rs
