1use crate::Result;
2use std::collections::VecDeque;
3
4pub struct StartCodeScanner {
5 buffer: Vec<u8>,
6 ready_spans: VecDeque<NalSpan>,
7 pending_start: Option<(usize, u8)>,
8}
9
10impl StartCodeScanner {
11 pub fn new() -> Self {
12 Self {
13 buffer: Vec::new(),
14 ready_spans: VecDeque::new(),
15 pending_start: None,
16 }
17 }
18
19 pub fn push(&mut self, data: &[u8]) {
20 let prev_len = self.buffer.len();
21 self.buffer.extend_from_slice(data);
22 let scan_start = prev_len.saturating_sub(3);
23 self.scan_for_new_start_codes(scan_start);
24 }
25
26 pub fn next_nal_unit(&mut self) -> Result<Option<NalSpan>> {
27 if let Some(span) = self.ready_spans.pop_front() {
28 return Ok(Some(span));
29 }
30
31 self.scan_for_new_start_codes(self.buffer.len().saturating_sub(3));
32 Ok(self.ready_spans.pop_front())
33 }
34
35 pub fn finish_pending(&mut self) -> Option<NalSpan> {
36 self.scan_for_new_start_codes(self.buffer.len().saturating_sub(3));
37
38 if let Some(span) = self.ready_spans.pop_front() {
39 return Some(span);
40 }
41
42 if let Some((start_pos, start_code_len)) = self.pending_start.take() {
43 let data_start = start_pos + start_code_len as usize;
44 if data_start < self.buffer.len() {
45 return Some(NalSpan {
46 start_pos,
47 start_code_len,
48 data_start,
49 data_end: self.buffer.len(),
50 });
51 }
52 }
53
54 None
55 }
56
57 pub fn get_nal_data(&self, span: &NalSpan) -> &[u8] {
58 &self.buffer[span.data_start..span.data_end]
59 }
60
61 pub fn has_pending_start(&self) -> bool {
62 self.pending_start.is_some()
63 }
64
65 pub fn consume_processed(&mut self, up_to: usize) {
66 if up_to == 0 || up_to > self.buffer.len() {
67 return;
68 }
69
70 self.buffer.drain(0..up_to);
71
72 if let Some((start_pos, start_code_len)) = self.pending_start {
73 if start_pos >= up_to {
74 self.pending_start = Some((start_pos - up_to, start_code_len));
75 } else if start_pos + start_code_len as usize > up_to {
76 self.pending_start = Some((0, start_code_len));
77 } else {
78 self.pending_start = None;
79 }
80 }
81
82 for span in &mut self.ready_spans {
83 if span.start_pos >= up_to {
84 span.start_pos -= up_to;
85 span.data_start -= up_to;
86 span.data_end -= up_to;
87 } else {
88 span.start_pos = 0;
89 span.data_start = 0;
90 span.data_end = span.data_end.saturating_sub(up_to);
91 }
92 }
93 }
94
95 pub fn reset(&mut self) {
96 self.buffer.clear();
97 self.ready_spans.clear();
98 self.pending_start = None;
99 }
100
101 fn scan_for_new_start_codes(&mut self, mut index: usize) {
102 if index > self.buffer.len() {
103 index = self.buffer.len();
104 }
105
106 while index + 2 < self.buffer.len() {
107 if self.buffer[index] == 0x00 && self.buffer[index + 1] == 0x00 {
108 if index + 3 < self.buffer.len()
109 && self.buffer[index + 2] == 0x00
110 && self.buffer[index + 3] == 0x01
111 {
112 self.record_start_code(index, 4);
113 index += 1;
114 continue;
115 } else if self.buffer[index + 2] == 0x01 {
116 self.record_start_code(index, 3);
117 index += 1;
118 continue;
119 }
120 }
121 index += 1;
122 }
123 }
124
125 fn record_start_code(&mut self, start_pos: usize, start_code_len: u8) {
126 if let Some((pending_pos, pending_len)) = self.pending_start {
127 if pending_pos == start_pos {
128 return;
129 }
130
131 let data_start = pending_pos + pending_len as usize;
132 if start_pos < data_start {
133 return;
135 }
136
137 if data_start < start_pos {
138 self.ready_spans.push_back(NalSpan {
139 start_pos: pending_pos,
140 start_code_len: pending_len,
141 data_start,
142 data_end: start_pos,
143 });
144 }
145 }
146
147 self.pending_start = Some((start_pos, start_code_len));
148 }
149}
150
151#[derive(Debug, Clone)]
152pub struct NalSpan {
153 pub start_pos: usize,
154 pub start_code_len: u8,
155 pub data_start: usize,
156 pub data_end: usize,
157}
158
159impl NalSpan {
160 pub fn len(&self) -> usize {
161 self.data_end - self.data_start
162 }
163}
164
165#[cfg(test)]
166mod tests {
167 use super::*;
168
169 #[test]
170 fn test_find_start_codes() {
171 let mut scanner = StartCodeScanner::new();
172 scanner.push(&[0x00, 0x00, 0x01, 0x42, 0x00, 0x00, 0x00, 0x01, 0x43]);
173
174 let nal1 = scanner.next_nal_unit().unwrap().unwrap();
175 assert_eq!(nal1.start_code_len, 3);
176 assert_eq!(scanner.get_nal_data(&nal1), &[0x42]);
177
178 scanner.consume_processed(nal1.data_end);
179 assert!(scanner.next_nal_unit().unwrap().is_none());
180
181 let nal2 = scanner.finish_pending().unwrap();
182 assert_eq!(nal2.start_code_len, 4);
183 assert_eq!(scanner.get_nal_data(&nal2), &[0x43]);
184 }
185
186 #[test]
187 fn test_streaming() {
188 let mut scanner = StartCodeScanner::new();
189
190 scanner.push(&[0x00, 0x00]);
191 assert!(scanner.next_nal_unit().unwrap().is_none());
192
193 scanner.push(&[0x01, 0x42, 0x00]);
194 assert!(scanner.next_nal_unit().unwrap().is_none());
195
196 scanner.push(&[0x00, 0x01, 0x43]);
197 let first = scanner.next_nal_unit().unwrap().unwrap();
198 assert_eq!(scanner.get_nal_data(&first), &[0x42]);
199 scanner.consume_processed(first.data_end);
200
201 let second = scanner.finish_pending().unwrap();
202 assert_eq!(scanner.get_nal_data(&second), &[0x43]);
203 }
204
205 #[test]
206 fn test_finish_pending_at_end_of_stream() {
207 let mut scanner = StartCodeScanner::new();
208 scanner.push(&[0x00, 0x00, 0x01, 0x43, 0x55]);
209
210 assert!(scanner.next_nal_unit().unwrap().is_none());
211
212 let flushed = scanner.finish_pending().unwrap();
213 assert_eq!(flushed.start_code_len, 3);
214 assert_eq!(scanner.get_nal_data(&flushed), &[0x43, 0x55]);
215 }
216
217 #[test]
218 fn test_incomplete_start_code_across_chunks() {
219 let mut scanner = StartCodeScanner::new();
220 scanner.push(&[0x00, 0x00, 0x00]);
221 assert!(scanner.next_nal_unit().unwrap().is_none());
222
223 scanner.push(&[0x01, 0x45, 0x00, 0x00]);
224 assert!(scanner.next_nal_unit().unwrap().is_none());
225
226 let nal = scanner.finish_pending().unwrap();
227 assert_eq!(nal.start_code_len, 4);
228 let data = scanner.get_nal_data(&nal);
229 assert_eq!(data.first(), Some(&0x45));
230 }
231}