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Copy pathes.rs
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657 lines (620 loc) · 23.9 KB
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//! Splitting elementary streams into access units while the file is scanned.
//!
//! The scanners feed each stream's payload bytes chunk by chunk (a TS packet's payload, a PS
//! packet's payload). A chunk is identified by the position the reader restarts from (`pos`) and
//! the elementary-stream offset of its first byte. Splitting needs only a few bytes beyond a
//! boundary, so only the most recent chunks are remembered.
use std::collections::VecDeque;
use crate::{Codec, PictureInfo, Unit};
/// How a stream is cut into units.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum Mode {
/// MPEG-1/2 video: one coded frame (a frame picture or two field pictures) per unit.
MpegVideo,
/// H.264 / HEVC: one PES packet (with a timestamp) per unit; NAL types give the flags.
Nal { hevc: bool },
/// Framed audio with self-describing frame headers.
Audio(AudioSync),
/// One PES packet per unit.
Pes,
}
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub(crate) enum AudioSync {
Mpa,
Adts,
Loas,
Ac3,
}
impl Mode {
fn of(codec: &Codec) -> Mode {
match codec {
Codec::Mpeg1Video | Codec::Mpeg2Video => Mode::MpegVideo,
Codec::H264 => Mode::Nal { hevc: false },
Codec::Hevc => Mode::Nal { hevc: true },
Codec::MpegAudio => Mode::Audio(AudioSync::Mpa),
Codec::AacAdts => Mode::Audio(AudioSync::Adts),
Codec::AacLatm => Mode::Audio(AudioSync::Loas),
Codec::Ac3 | Codec::Eac3 => Mode::Audio(AudioSync::Ac3),
_ => Mode::Pes,
}
}
}
#[derive(Clone, Copy)]
struct PesMark {
es_start: u64,
pts: Option<i64>,
dts: Option<i64>,
used: bool,
}
/// A unit whose end is not known yet.
#[derive(Clone, Copy)]
struct Open {
start: u64,
pos: u64,
offset: u32,
pts: Option<i64>,
dts: Option<i64>,
key: bool,
disposable: bool,
/// A coded slice has been seen (H.264 / HEVC).
vcl: bool,
picture: Option<PictureInfo>,
}
/// MPEG video picture waiting for its coding extension (to tell fields from frames).
#[derive(Clone, Copy)]
struct PendingPicture {
/// Start of the unit if the picture begins one (its first sequence / GOP header).
unit_start: u64,
/// The picture start code (timestamps belong to the unit whose picture starts in the PES).
at: u64,
info: PictureInfo,
}
pub(crate) struct Splitter {
mode: Mode,
/// Elementary-stream bytes fed so far.
es_pos: u64,
/// Recent chunks: (reader position, ES offset of the first byte).
chunks: VecDeque<(u64, u64)>,
pes: VecDeque<PesMark>,
/// Unconsumed bytes (start codes / frame headers spanning chunks), starting at `buf_start`.
buf: Vec<u8>,
buf_start: u64,
open: Option<Open>,
pub units: Vec<Unit>,
pub skipped: u64,
// MPEG video state
header_start: Option<u64>,
seq_in_unit: bool,
gop: Option<(bool, bool)>,
pending: Option<PendingPicture>,
open_field: Option<u8>,
// audio state
next_frame: Option<u64>,
}
/// AC-3 frame sizes in 16-bit words for 48 / 44.1 / 32 kHz (A/52 Table 5.18), by
/// frmsizecod / 2; 44.1 kHz adds a word for odd frmsizecod.
const AC3_KBPS: [u32; 19] = [32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 448, 512, 576, 640];
pub(crate) fn ac3_frame_bytes(fscod: u8, frmsizecod: u8) -> Option<usize> {
let kbps = *AC3_KBPS.get((frmsizecod / 2) as usize)?;
let words = match fscod {
0 => kbps * 2,
1 => kbps * 96_000 / 44_100 + (frmsizecod & 1) as u32,
2 => kbps * 3,
_ => return None,
};
Some(words as usize * 2)
}
const MPA_KBPS: [[u16; 15]; 5] = [
[0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448], // MPEG-1 layer I
[0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384], // MPEG-1 layer II
[0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320], // MPEG-1 layer III
[0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256], // MPEG-2/2.5 layer I
[0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160], // MPEG-2/2.5 layers II, III
];
/// MPEG audio frame header (ISO/IEC 11172-3 §2.4.2.3, 13818-3 LSF): (frame bytes, sample rate,
/// samples per frame).
pub(crate) fn mpa_header(b: &[u8]) -> Option<(usize, u32, u32)> {
if b.len() < 4 || b[0] != 0xFF || b[1] & 0xE0 != 0xE0 {
return None;
}
let version = (b[1] >> 3) & 3; // 0: 2.5, 2: MPEG-2, 3: MPEG-1
let layer = (b[1] >> 1) & 3; // 3: I, 2: II, 1: III
let br = (b[2] >> 4) as usize;
let sr = (b[2] >> 2) & 3;
let pad = ((b[2] >> 1) & 1) as usize;
if version == 1 || layer == 0 || br == 0 || br == 15 || sr == 3 {
return None;
}
let rate = [44_100u32, 48_000, 32_000][sr as usize]
>> match version {
3 => 0,
2 => 1,
_ => 2,
};
let table = match (version == 3, layer) {
(true, 3) => 0,
(true, 2) => 1,
(true, _) => 2,
(false, 3) => 3,
(false, _) => 4,
};
let kbps = MPA_KBPS[table][br] as usize;
let (bytes, samples) = match layer {
3 => ((12 * kbps * 1000 / rate as usize + pad) * 4, 384),
2 => (144 * kbps * 1000 / rate as usize + pad, 1152),
_ if version == 3 => (144 * kbps * 1000 / rate as usize + pad, 1152),
_ => (72 * kbps * 1000 / rate as usize + pad, 576),
};
(bytes >= 4).then_some((bytes, rate, samples))
}
/// What an audio frame header says.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct FrameInfo {
pub sample_rate: u32,
pub channels: u32,
/// Samples per channel in the frame.
pub samples: u32,
/// MPEG audio layer (1-3); AC-3 bsid; ADTS object type (profile + 1).
pub variant: u8,
}
const ADTS_RATES: [u32; 13] = [96_000, 88_200, 64_000, 48_000, 44_100, 32_000, 24_000, 22_050, 16_000, 12_000, 11_025, 8_000, 7_350];
/// Parse the frame header at the start of `b` (MPEG audio, ADTS, AC-3, E-AC-3).
pub fn frame_info(codec: &Codec, b: &[u8]) -> Option<FrameInfo> {
match codec {
Codec::MpegAudio => {
let (_, sample_rate, samples) = mpa_header(b)?;
let layer = 4 - ((b[1] >> 1) & 3);
Some(FrameInfo { sample_rate, channels: if b[3] >> 6 == 3 { 1 } else { 2 }, samples, variant: layer })
}
Codec::AacAdts => {
frame_len(AudioSync::Adts, b)?;
let sf = ((b[2] >> 2) & 15) as usize;
let ch = (((b[2] & 1) << 2) | (b[3] >> 6)) as u32;
Some(FrameInfo {
sample_rate: *ADTS_RATES.get(sf)?,
channels: if ch == 0 {
2
} else if ch == 7 {
8
} else {
ch
},
samples: 1024 * ((b[6] & 3) as u32 + 1),
variant: (b[2] >> 6) + 1,
})
}
Codec::Ac3 | Codec::Eac3 => {
frame_len(AudioSync::Ac3, b)?;
let bsid = b[5] >> 3;
if bsid > 10 {
// E-AC-3: fscod(2) numblkscod(2) acmod(3) lfeon(1)
let fscod = b[4] >> 6;
let (rate, blocks) = if fscod == 3 {
([24_000, 22_050, 16_000, 0][((b[4] >> 4) & 3) as usize], 6)
} else {
([48_000, 44_100, 32_000][fscod as usize], [1, 2, 3, 6][((b[4] >> 4) & 3) as usize])
};
let acmod = (b[4] >> 1) & 7;
return Some(FrameInfo { sample_rate: rate, channels: AC3_CHANNELS[acmod as usize] + (b[4] & 1) as u32, samples: 256 * blocks, variant: bsid });
}
let fscod = b[4] >> 6;
let rate = *[48_000u32, 44_100, 32_000].get(fscod as usize)?;
// bsi: bsid(5) bsmod(3) acmod(3) [cmixlev(2)] [surmixlev(2)] [dsurmod(2)] lfeon(1)
let acmod = b[6] >> 5;
let mut bit = 3; // bits of byte 6 consumed
if acmod & 1 != 0 && acmod != 1 {
bit += 2;
}
if acmod & 4 != 0 {
bit += 2;
}
if acmod == 2 {
bit += 2;
}
let word = u16::from_be_bytes([b[6], *b.get(7)?]);
let lfe = (word >> (15 - bit)) & 1;
Some(FrameInfo { sample_rate: rate, channels: AC3_CHANNELS[acmod as usize] + lfe as u32, samples: 1536, variant: bsid })
}
_ => None,
}
}
/// Full-bandwidth channels per AC-3 audio coding mode (A/52 Table 5.8).
const AC3_CHANNELS: [u32; 8] = [2, 1, 2, 3, 3, 4, 4, 5];
/// Frame length at the start of `b` for the given sync type (`None`: no valid header; `Some(0)`
/// is never returned).
fn frame_len(sync: AudioSync, b: &[u8]) -> Option<usize> {
match sync {
AudioSync::Mpa => mpa_header(b).map(|h| h.0),
AudioSync::Adts => {
if b.len() < 7 || b[0] != 0xFF || b[1] & 0xF6 != 0xF0 {
return None;
}
let len = ((b[3] as usize & 3) << 11) | (b[4] as usize) << 3 | (b[5] as usize) >> 5;
(len >= 7).then_some(len)
}
AudioSync::Loas => {
if b.len() < 3 || b[0] != 0x56 || b[1] & 0xE0 != 0xE0 {
return None;
}
let len = ((b[1] as usize & 0x1F) << 8) | b[2] as usize;
(len > 0).then_some(len + 3)
}
AudioSync::Ac3 => {
if b.len() < 6 || b[0] != 0x0B || b[1] != 0x77 {
return None;
}
let bsid = b[5] >> 3;
if bsid <= 10 {
ac3_frame_bytes(b[4] >> 6, b[4] & 0x3F)
} else if bsid <= 16 {
// E-AC-3: frmsiz
Some(((((b[2] & 7) as usize) << 8) | b[3] as usize) * 2 + 2)
} else {
None
}
}
}
}
impl Splitter {
pub fn new(codec: &Codec) -> Splitter {
Splitter {
mode: Mode::of(codec),
es_pos: 0,
chunks: VecDeque::new(),
pes: VecDeque::new(),
buf: Vec::new(),
buf_start: 0,
open: None,
units: Vec::new(),
skipped: 0,
header_start: None,
seq_in_unit: false,
gop: None,
pending: None,
open_field: None,
next_frame: None,
}
}
/// A PES packet starts (its payload follows in the next chunks).
pub fn pes_start(&mut self, pts: Option<i64>, dts: Option<i64>) {
self.pes.push_back(PesMark { es_start: self.es_pos, pts, dts, used: false });
while self.pes.len() > 64 {
self.pes.pop_front();
}
match self.mode {
Mode::Pes => self.begin_pes_unit(true),
Mode::Nal { .. } => self.begin_pes_unit(pts.is_some() || dts.is_some()),
_ => {}
}
}
/// PES-delimited units: a packet with a timestamp (or any packet in plain PES mode) starts a
/// new unit; one without continues the previous unit.
fn begin_pes_unit(&mut self, new: bool) {
if !new && self.open.is_some() {
return;
}
let at = self.es_pos;
self.close(at);
// the chunk of this position arrives with the next feed: resolved there
let mut o = Open { start: at, pos: u64::MAX, offset: 0, pts: None, dts: None, key: false, disposable: false, vcl: false, picture: None };
if let Some((pts, dts)) = self.timestamps_at(at) {
o.pts = pts;
o.dts = dts;
}
if self.mode == Mode::Pes {
o.key = true;
}
self.open = Some(o);
}
/// The unused timestamps of the PES packet holding `at` (consumed).
fn timestamps_at(&mut self, at: u64) -> Option<(Option<i64>, Option<i64>)> {
let m = self.pes.iter_mut().rev().find(|m| m.es_start <= at)?;
if m.used || (m.pts.is_none() && m.dts.is_none()) {
return None;
}
m.used = true;
Some((m.pts, m.dts))
}
/// Reader position and offset of elementary-stream byte `at`.
fn locate(&self, at: u64) -> Option<(u64, u32)> {
let c = self.chunks.iter().rev().find(|c| c.1 <= at)?;
Some((c.0, (at - c.1) as u32))
}
/// End the open unit at `end`.
fn close(&mut self, end: u64) {
let Some(o) = self.open.take() else { return };
if end <= o.start || o.pos == u64::MAX {
return;
}
let size = (end - o.start).min(u32::MAX as u64) as u32;
self.units.push(Unit { pts: o.pts, dts: o.dts, key: o.key, disposable: o.disposable, size, pos: o.pos, offset: o.offset, picture: o.picture });
}
/// Payload bytes of one chunk (`pos`: where the reader restarts to find them).
pub fn feed(&mut self, pos: u64, data: &[u8]) {
if data.is_empty() {
return;
}
self.chunks.push_back((pos, self.es_pos));
if let Some(o) = self.open.as_mut()
&& o.pos == u64::MAX
&& o.start == self.es_pos
{
o.pos = pos;
o.offset = 0;
}
let start = self.es_pos;
self.es_pos += data.len() as u64;
match self.mode {
Mode::Pes => {}
Mode::Nal { hevc } => self.scan_nal(start, data, hevc),
Mode::MpegVideo => self.scan_mpeg(start, data),
Mode::Audio(sync) => self.scan_audio(start, data, sync),
}
// forget chunks no pending position can refer to
let keep_from = self.buf_start.min(self.pending.map_or(u64::MAX, |p| p.unit_start.min(p.at))).min(self.header_start.unwrap_or(u64::MAX));
while self.chunks.len() > 2 && self.chunks[1].1 <= keep_from {
self.chunks.pop_front();
}
}
/// Append to the window and return it with its start.
fn window(&mut self, start: u64, data: &[u8]) {
if self.buf.is_empty() || self.buf_start + self.buf.len() as u64 != start {
self.buf.clear();
self.buf_start = start;
}
self.buf.extend_from_slice(data);
}
/// Keep only the last `keep` bytes of the window.
fn trim(&mut self, keep: usize) {
if self.buf.len() > keep {
let drop = self.buf.len() - keep;
self.buf.drain(..drop);
self.buf_start += drop as u64;
}
}
/// Start codes in the window from index `from`: (window index of `00 00 01`, code).
fn next_start_code(&self, from: usize) -> Option<usize> {
let b = &self.buf;
let mut i = from;
while i + 3 <= b.len() {
match b[i + 2] {
1 if b[i] == 0 && b[i + 1] == 0 => return Some(i),
0 => i += 1,
_ => i += 3,
}
}
None
}
fn scan_nal(&mut self, start: u64, data: &[u8], hevc: bool) {
self.window(start, data);
let mut i = 0;
let mut blocked = None;
while let Some(k) = self.next_start_code(i) {
// NAL header byte(s) needed
if k + 5 > self.buf.len() {
blocked = Some(k);
break;
}
let h = self.buf[k + 3];
let (key, vcl, non_ref) = if hevc {
let t = (h >> 1) & 0x3F;
(
(16..=23).contains(&t),
t < 32,
// sub-layer non-reference pictures (TRAIL_N, TSA_N, STSA_N, RADL_N, RASL_N)
t < 16 && t.is_multiple_of(2),
)
} else {
let t = h & 0x1F;
(t == 5, (1..=5).contains(&t), h & 0x60 == 0)
};
if let Some(o) = self.open.as_mut()
&& vcl
{
o.key |= key;
// disposable while every slice is non-reference
o.disposable = if o.vcl { o.disposable && non_ref } else { non_ref };
o.vcl = true;
}
i = k + 3;
}
self.keep_tail(i, blocked);
}
/// Drop the scanned part of the window: keep from a start code waiting for more bytes, or
/// the last bytes a split start code may begin in.
fn keep_tail(&mut self, i: usize, blocked: Option<usize>) {
let len = self.buf.len();
let resume = blocked.unwrap_or_else(|| i.max(len.saturating_sub(3)));
self.trim(len - resume.min(len));
}
fn scan_mpeg(&mut self, start: u64, data: &[u8]) {
self.window(start, data);
let mut i = 0;
let mut blocked = None;
while let Some(k) = self.next_start_code(i) {
// up to 5 bytes after the code are inspected
if k + 9 > self.buf.len() {
blocked = Some(k);
break;
}
let at = self.buf_start + k as u64;
let code = self.buf[k + 3];
let p = [self.buf[k + 4], self.buf[k + 5], self.buf[k + 6], self.buf[k + 7], self.buf[k + 8]];
match code {
0xB3 => {
self.settle_pending();
self.header_start.get_or_insert(at);
self.seq_in_unit = true;
}
0xB8 => {
self.settle_pending();
self.header_start.get_or_insert(at);
self.gop = Some((p[3] & 0x40 != 0, p[3] & 0x20 != 0));
}
0x00 => {
self.settle_pending();
let info = PictureInfo {
coding_type: (p[1] >> 3) & 7,
temporal_reference: ((p[0] as u16) << 2) | (p[1] >> 6) as u16,
structure: 3,
progressive_frame: true,
sequence_header: self.seq_in_unit,
gop: self.gop.is_some(),
closed_gop: self.gop.is_some_and(|g| g.0),
broken_link: self.gop.is_some_and(|g| g.1),
..Default::default()
};
let unit_start = self.header_start.take().unwrap_or(at);
self.seq_in_unit = false;
self.gop = None;
self.pending = Some(PendingPicture { unit_start, at, info });
}
0xB5 if p[0] >> 4 == 8 => {
if let Some(pp) = self.pending.as_mut() {
pp.info.structure = p[2] & 3;
pp.info.top_field_first = p[3] & 0x80 != 0;
pp.info.repeat_first_field = p[3] & 0x02 != 0;
pp.info.progressive_frame = p[4] & 0x80 != 0;
}
self.settle_pending();
}
0xB5 | 0xB2 => {}
_ => self.settle_pending(),
}
i = k + 3;
}
self.keep_tail(i, blocked);
}
/// A picture's structure is known: start a unit, or join a first field.
fn settle_pending(&mut self) {
let Some(pp) = self.pending.take() else { return };
let s = pp.info.structure;
if let Some(first) = self.open_field
&& s != 3
&& first != s
&& s != 0
{
self.open_field = None;
return;
}
self.close(pp.unit_start);
let (pos, offset) = self.locate(pp.unit_start).unwrap_or((u64::MAX, 0));
let mut o = Open {
start: pp.unit_start,
pos,
offset,
pts: None,
dts: None,
key: matches!(pp.info.coding_type, 1 | 4),
disposable: pp.info.coding_type == 3,
vcl: true,
picture: Some(pp.info),
};
if let Some((pts, dts)) = self.timestamps_at(pp.at) {
o.pts = pts;
o.dts = dts;
}
self.open = Some(o);
self.open_field = (s == 1 || s == 2).then_some(s);
}
fn scan_audio(&mut self, start: u64, data: &[u8], sync: AudioSync) {
let end = start + data.len() as u64;
// skip whole chunks inside the current frame
if let Some(n) = self.next_frame
&& n >= end
{
return;
}
self.window(start, data);
loop {
let at = match self.next_frame {
Some(n) if n >= self.buf_start => n,
_ => self.buf_start,
};
let i = (at - self.buf_start) as usize;
if i + 8 > self.buf.len() {
// not enough bytes for a header yet
self.trim(self.buf.len().saturating_sub(i));
return;
}
match frame_len(sync, &self.buf[i..]) {
Some(len) if self.next_frame == Some(at) || self.confirmed(sync, i, len) => {
self.close(at);
let (pos, offset) = self.locate(at).unwrap_or((u64::MAX, 0));
let mut o = Open { start: at, pos, offset, pts: None, dts: None, key: true, disposable: false, vcl: false, picture: None };
if let Some((pts, dts)) = self.timestamps_at(at) {
o.pts = pts;
o.dts = dts;
}
self.open = Some(o);
self.next_frame = Some(at + len as u64);
if at + len as u64 >= self.buf_start + self.buf.len() as u64 {
self.buf.clear();
self.buf_start = at + len as u64;
return;
}
}
_ => {
// lost sync: look for the next header from the following byte
self.next_frame = None;
self.skipped += 1;
let next = self.buf[i + 1..]
.iter()
.position(|&b| matches!((sync, b), (AudioSync::Ac3, 0x0B) | (AudioSync::Loas, 0x56) | (AudioSync::Mpa | AudioSync::Adts, 0xFF)));
match next {
Some(d) => {
self.skipped += d as u64;
self.trim(self.buf.len() - (i + 1 + d));
}
None => {
self.skipped += (self.buf.len() - i - 1) as u64;
self.trim(0);
return;
}
}
}
}
}
}
/// A header found while hunting for sync is accepted when the next frame's header follows
/// it (or the data ends before it).
fn confirmed(&self, sync: AudioSync, i: usize, len: usize) -> bool {
let j = i + len;
if j + 8 > self.buf.len() {
return true;
}
frame_len(sync, &self.buf[j..]).is_some()
}
/// End of stream: close the open unit.
pub fn finish(&mut self) {
self.settle_pending();
let end = match (self.mode, self.next_frame) {
(Mode::Audio(_), Some(n)) => n.min(self.es_pos),
_ => self.es_pos,
};
if let (Mode::Audio(_), Some(o)) = (self.mode, self.open) {
// a truncated last frame is dropped
if self.next_frame.is_some_and(|n| n > self.es_pos) {
self.skipped += self.es_pos - o.start;
self.open = None;
}
}
self.close(end);
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn audio_frame_sizes() {
// MPEG-1 layer II 48 kHz 192 kb/s: 576 bytes; layer III 44.1 kHz 128 kb/s with padding: 418
assert_eq!(mpa_header(&[0xFF, 0xFD, 0xA4, 0x00]), Some((576, 48_000, 1152)));
assert_eq!(mpa_header(&[0xFF, 0xFB, 0x92, 0x00]), Some((418, 44_100, 1152)));
// MPEG-2 layer III 24 kHz 64 kb/s: 192 bytes, 576 samples
assert_eq!(mpa_header(&[0xFF, 0xF3, 0x84, 0x00]), Some((192, 24_000, 576)));
// AC-3 448 kb/s at 48 kHz = 1792 bytes; 44.1 kHz 192 kb/s odd code = 836 bytes
assert_eq!(ac3_frame_bytes(0, 30), Some(1792));
assert_eq!(ac3_frame_bytes(1, 21), Some(836));
assert_eq!(ac3_frame_bytes(2, 0), Some(192));
}
}