dvb_si/descriptors/
enhanced_ac3.rs

1//! Enhanced AC-3 Descriptor — ETSI EN 300 468 Annex D (tag 0x7A).
2//!
3//! Carried inside PMT's ES_info loop for Enhanced AC-3 (E-AC-3, Dolby Digital
4//! Plus) audio components.  The layout is a single flags byte whose eight bits
5//! are all assigned (no reserved nibble, unlike the AC-3 descriptor), followed
6//! by up to seven optional 1-byte fields and an optional free-form
7//! `additional_info_byte` trailer.
8
9use super::ac3::Ac3ComponentType;
10use super::descriptor_body;
11use crate::error::{Error, Result};
12use dvb_common::{Parse, Serialize};
13
14/// Descriptor tag for Enhanced AC-3 (E-AC-3, Dolby Digital Plus).
15pub const TAG: u8 = 0x7A;
16const HEADER_LEN: usize = 2;
17
18const FLAG_COMPONENT_TYPE: u8 = 0x80;
19const FLAG_BSID: u8 = 0x40;
20const FLAG_MAINID: u8 = 0x20;
21const FLAG_ASVC: u8 = 0x10;
22const FLAG_MIXINFO_EXISTS: u8 = 0x08;
23const FLAG_SUBSTREAM1: u8 = 0x04;
24const FLAG_SUBSTREAM2: u8 = 0x02;
25const FLAG_SUBSTREAM3: u8 = 0x01;
26
27/// Enhanced AC-3 Descriptor — EN 300 468 Annex D (tag 0x7A).
28#[derive(Debug, Clone, PartialEq, Eq)]
29#[cfg_attr(feature = "serde", derive(serde::Serialize))]
30#[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
31pub struct EnhancedAc3Descriptor<'a> {
32    /// AC-3 component_type (layout per Annex D).
33    pub component_type: Option<u8>,
34    /// Bit stream identification.
35    pub bsid: Option<u8>,
36    /// Main audio service id.
37    pub mainid: Option<u8>,
38    /// Associated service id.
39    pub asvc: Option<u8>,
40    /// mixinfoexists flag — indicates whether mixing metadata is present in
41    /// the enhanced AC-3 bit stream.
42    pub mixinfoexists: bool,
43    /// Sub-stream 1 identification.
44    pub substream1: Option<u8>,
45    /// Sub-stream 2 identification.
46    pub substream2: Option<u8>,
47    /// Sub-stream 3 identification.
48    pub substream3: Option<u8>,
49    /// Raw trailing `additional_info_byte` run.
50    pub additional_info: &'a [u8],
51}
52
53impl EnhancedAc3Descriptor<'_> {
54    /// Decodes the optional `component_type` field per ETSI EN 300 468 Annex D.
55    ///
56    /// Returns `None` when `component_type` is `None`.
57    #[must_use]
58    pub fn decoded_component_type(&self) -> Option<Ac3ComponentType> {
59        Some(Ac3ComponentType::from_byte(self.component_type?))
60    }
61}
62
63impl<'a> Parse<'a> for EnhancedAc3Descriptor<'a> {
64    type Error = crate::error::Error;
65    fn parse(bytes: &'a [u8]) -> Result<Self> {
66        let body = descriptor_body(
67            bytes,
68            TAG,
69            "EnhancedAc3Descriptor",
70            "unexpected tag for EAC-3 descriptor",
71        )?;
72        if body.is_empty() {
73            return Err(Error::InvalidDescriptor {
74                tag: TAG,
75                reason: "descriptor body is empty (length=0)",
76            });
77        }
78        let flags = body[0];
79        let mixinfoexists = (flags & FLAG_MIXINFO_EXISTS) != 0;
80        let mut pos = 1;
81        let mut read_one = |set: bool| -> Result<Option<u8>> {
82            if !set {
83                return Ok(None);
84            }
85            if pos >= body.len() {
86                return Err(Error::InvalidDescriptor {
87                    tag: TAG,
88                    reason: "enhanced AC-3 descriptor flags claim more bytes than length permits",
89                });
90            }
91            let b = body[pos];
92            pos += 1;
93            Ok(Some(b))
94        };
95
96        let component_type = read_one(flags & FLAG_COMPONENT_TYPE != 0)?;
97        let bsid = read_one(flags & FLAG_BSID != 0)?;
98        let mainid = read_one(flags & FLAG_MAINID != 0)?;
99        let asvc = read_one(flags & FLAG_ASVC != 0)?;
100        let substream1 = read_one(flags & FLAG_SUBSTREAM1 != 0)?;
101        let substream2 = read_one(flags & FLAG_SUBSTREAM2 != 0)?;
102        let substream3 = read_one(flags & FLAG_SUBSTREAM3 != 0)?;
103        let additional_info = &body[pos..];
104        Ok(Self {
105            component_type,
106            bsid,
107            mainid,
108            asvc,
109            mixinfoexists,
110            substream1,
111            substream2,
112            substream3,
113            additional_info,
114        })
115    }
116}
117
118impl Serialize for EnhancedAc3Descriptor<'_> {
119    type Error = crate::error::Error;
120    fn serialized_len(&self) -> usize {
121        HEADER_LEN
122            + 1
123            + usize::from(self.component_type.is_some())
124            + usize::from(self.bsid.is_some())
125            + usize::from(self.mainid.is_some())
126            + usize::from(self.asvc.is_some())
127            + usize::from(self.substream1.is_some())
128            + usize::from(self.substream2.is_some())
129            + usize::from(self.substream3.is_some())
130            + self.additional_info.len()
131    }
132
133    fn serialize_into(&self, buf: &mut [u8]) -> Result<usize> {
134        let len = self.serialized_len();
135        if buf.len() < len {
136            return Err(Error::OutputBufferTooSmall {
137                need: len,
138                have: buf.len(),
139            });
140        }
141        buf[0] = TAG;
142        buf[1] = (len - HEADER_LEN) as u8;
143        let mut flags: u8 = 0;
144        if self.component_type.is_some() {
145            flags |= FLAG_COMPONENT_TYPE;
146        }
147        if self.bsid.is_some() {
148            flags |= FLAG_BSID;
149        }
150        if self.mainid.is_some() {
151            flags |= FLAG_MAINID;
152        }
153        if self.asvc.is_some() {
154            flags |= FLAG_ASVC;
155        }
156        if self.mixinfoexists {
157            flags |= FLAG_MIXINFO_EXISTS;
158        }
159        if self.substream1.is_some() {
160            flags |= FLAG_SUBSTREAM1;
161        }
162        if self.substream2.is_some() {
163            flags |= FLAG_SUBSTREAM2;
164        }
165        if self.substream3.is_some() {
166            flags |= FLAG_SUBSTREAM3;
167        }
168        buf[2] = flags;
169        let mut pos = 3;
170        for b in [
171            self.component_type,
172            self.bsid,
173            self.mainid,
174            self.asvc,
175            self.substream1,
176            self.substream2,
177            self.substream3,
178        ]
179        .into_iter()
180        .flatten()
181        {
182            buf[pos] = b;
183            pos += 1;
184        }
185        buf[pos..pos + self.additional_info.len()].copy_from_slice(self.additional_info);
186        Ok(len)
187    }
188}
189impl<'a> crate::traits::DescriptorDef<'a> for EnhancedAc3Descriptor<'a> {
190    const TAG: u8 = TAG;
191    const NAME: &'static str = "ENHANCED_AC3";
192}
193
194#[cfg(test)]
195mod tests {
196    use super::*;
197    use crate::descriptors::ac3::{Ac3ChannelMode, Ac3ServiceType};
198
199    #[test]
200    fn parse_with_all_fields() {
201        let bytes = [
202            TAG,
203            8,
204            FLAG_COMPONENT_TYPE
205                | FLAG_BSID
206                | FLAG_MAINID
207                | FLAG_ASVC
208                | FLAG_MIXINFO_EXISTS
209                | FLAG_SUBSTREAM1
210                | FLAG_SUBSTREAM2
211                | FLAG_SUBSTREAM3,
212            0x11,
213            0x22,
214            0x33,
215            0x44,
216            0x55,
217            0x66,
218            0x77,
219        ];
220        let d = EnhancedAc3Descriptor::parse(&bytes).unwrap();
221        assert_eq!(d.component_type, Some(0x11));
222        assert_eq!(d.bsid, Some(0x22));
223        assert_eq!(d.mainid, Some(0x33));
224        assert_eq!(d.asvc, Some(0x44));
225        assert!(d.mixinfoexists);
226        assert_eq!(d.substream1, Some(0x55));
227        assert_eq!(d.substream2, Some(0x66));
228        assert_eq!(d.substream3, Some(0x77));
229        assert_eq!(d.additional_info, &[] as &[u8]);
230    }
231
232    #[test]
233    fn parse_with_only_component_type_and_mixinfoexists() {
234        let bytes = [TAG, 2, FLAG_COMPONENT_TYPE | FLAG_MIXINFO_EXISTS, 0x07];
235        let d = EnhancedAc3Descriptor::parse(&bytes).unwrap();
236        assert_eq!(d.component_type, Some(0x07));
237        assert!(d.mixinfoexists);
238        assert_eq!(d.bsid, None);
239        assert_eq!(d.substream1, None);
240    }
241
242    #[test]
243    fn parse_with_additional_info_only() {
244        let bytes = [TAG, 3, 0x00, 0xAA, 0xBB];
245        let d = EnhancedAc3Descriptor::parse(&bytes).unwrap();
246        assert_eq!(d.component_type, None);
247        assert!(!d.mixinfoexists);
248        assert_eq!(d.additional_info, &[0xAA, 0xBB]);
249    }
250
251    #[test]
252    fn decode_component_type_eac3_vi_stereo() {
253        // E-AC-3, full_service=0, service_type=2 (VI), channels=2 (stereo)
254        // bit7=1, bit6=0, bits[5:3]=010, bits[2:0]=010
255        // = 0b1_0_010_010 = 0x92
256        let d = EnhancedAc3Descriptor {
257            component_type: Some(0x92),
258            bsid: None,
259            mainid: None,
260            asvc: None,
261            mixinfoexists: false,
262            substream1: None,
263            substream2: None,
264            substream3: None,
265            additional_info: &[],
266        };
267        let ct = d.decoded_component_type().unwrap();
268        assert!(ct.enhanced_ac3);
269        assert!(!ct.full_service);
270        assert_eq!(ct.service_type, Ac3ServiceType::VisuallyImpaired);
271        assert_eq!(ct.channels, Ac3ChannelMode::Stereo);
272    }
273
274    #[test]
275    fn decode_component_type_full_service_cm_stereo() {
276        // AC-3, full_service=1, CM, stereo — same test as ac3.rs via shared from_byte
277        // 0x42 = bit7=0, bit6=1, bits[5:3]=000(CM), bits[2:0]=010(stereo)
278        let ct = Ac3ComponentType::from_byte(0x42);
279        assert!(!ct.enhanced_ac3);
280        assert!(ct.full_service);
281        assert_eq!(ct.service_type, Ac3ServiceType::CompleteMain);
282        assert_eq!(ct.channels, Ac3ChannelMode::Stereo);
283    }
284
285    #[test]
286    fn parse_rejects_wrong_tag() {
287        assert!(matches!(
288            EnhancedAc3Descriptor::parse(&[0x6A, 1, 0]).unwrap_err(),
289            Error::InvalidDescriptor { tag: 0x6A, .. }
290        ));
291    }
292
293    #[test]
294    fn parse_rejects_flags_past_length() {
295        let bytes = [TAG, 1, FLAG_COMPONENT_TYPE];
296        assert!(matches!(
297            EnhancedAc3Descriptor::parse(&bytes).unwrap_err(),
298            Error::InvalidDescriptor { .. }
299        ));
300    }
301
302    #[test]
303    fn parse_rejects_short_buffer() {
304        assert!(matches!(
305            EnhancedAc3Descriptor::parse(&[TAG]).unwrap_err(),
306            Error::BufferTooShort { .. }
307        ));
308    }
309
310    #[test]
311    fn serialize_round_trip() {
312        let d = EnhancedAc3Descriptor {
313            component_type: Some(0x40),
314            bsid: Some(8),
315            mainid: None,
316            asvc: None,
317            mixinfoexists: true,
318            substream1: Some(0xAA),
319            substream2: None,
320            substream3: None,
321            additional_info: &[0xFE, 0xED],
322        };
323        let mut buf = vec![0u8; d.serialized_len()];
324        d.serialize_into(&mut buf).unwrap();
325        assert_eq!(EnhancedAc3Descriptor::parse(&buf).unwrap(), d);
326    }
327
328    #[test]
329    fn serialize_round_trip_no_flags() {
330        let d = EnhancedAc3Descriptor {
331            component_type: None,
332            bsid: None,
333            mainid: None,
334            asvc: None,
335            mixinfoexists: false,
336            substream1: None,
337            substream2: None,
338            substream3: None,
339            additional_info: &[],
340        };
341        let mut buf = vec![0u8; d.serialized_len()];
342        d.serialize_into(&mut buf).unwrap();
343        assert_eq!(EnhancedAc3Descriptor::parse(&buf).unwrap(), d);
344        assert_eq!(buf, [TAG, 1, 0x00]);
345    }
346
347    #[test]
348    fn parse_rejects_empty_body() {
349        let bytes = [TAG, 0];
350        assert!(matches!(
351            EnhancedAc3Descriptor::parse(&bytes).unwrap_err(),
352            Error::InvalidDescriptor { .. }
353        ));
354    }
355}
dvb_si/descriptors/enhanced_ac3.rs

dvb_si/descriptors/
enhanced_ac3.rs
