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MPEG: Improve duration estimation

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Serial 2024-05-04 16:03:22 -04:00 committed by Alex
parent 4eae6e12a7
commit 24da5bac31
4 changed files with 108 additions and 52 deletions
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100
lofty/src/mpeg/header.rs
View file

@ -1,4 +1,5 @@
use super::constants::{BITRATES, PADDING_SIZES, SAMPLES, SAMPLE_RATES, SIDE_INFORMATION_SIZES};
use crate::config::ParsingMode;
use crate::error::Result;
use crate::macros::decode_err;
@ -49,10 +50,11 @@ where
// Unlike `search_for_frame_sync`, since this has the `Seek` bound, it will seek the reader
// back to the start of the header.
const REV_FRAME_SEARCH_BOUNDS: u64 = 1024;
pub(super) fn rev_search_for_frame_sync<R>(
pub(super) fn rev_search_for_frame_header<R>(
input: &mut R,
pos: &mut u64,
) -> std::io::Result<Option<u64>>
parse_mode: ParsingMode,
) -> Result<Option<Header>>
where
R: Read + Seek,
{
@ -61,15 +63,49 @@ where
*pos -= search_bounds;
input.seek(SeekFrom::Start(*pos))?;
let ret = search_for_frame_sync(&mut input.take(search_bounds));
if let Ok(Some(_)) = ret {
// Seek to the start of the frame sync
input.seek(SeekFrom::Current(-2))?;
let mut buf = Vec::with_capacity(search_bounds as usize);
input.take(search_bounds).read_to_end(&mut buf)?;
let mut frame_sync = [0u8; 2];
for (i, byte) in buf.iter().rev().enumerate() {
frame_sync[1] = frame_sync[0];
frame_sync[0] = *byte;
if verify_frame_sync(frame_sync) {
let relative_frame_start = (search_bounds as usize) - (i + 1);
if relative_frame_start + 4 > buf.len() {
if parse_mode == ParsingMode::Strict {
decode_err!(@BAIL Mpeg, "Expected full frame header (incomplete stream?)")
}
log::warn!("MPEG: Incomplete frame header, giving up");
break;
}
let header = Header::read(u32::from_be_bytes([
frame_sync[0],
frame_sync[1],
buf[relative_frame_start + 2],
buf[relative_frame_start + 3],
]));
// We need to check if the header is actually valid. For
// all we know, we could be in some junk (ex. 0xFF_FF_FF_FF).
if header.is_none() {
continue;
}
// Seek to the start of the frame sync
*pos += relative_frame_start as u64;
input.seek(SeekFrom::Start(*pos))?;
return Ok(header);
}
}
ret
Ok(None)
}
/// See [`cmp_header()`].
pub(crate) enum HeaderCmpResult {
Equal,
Undetermined,
@ -80,6 +116,18 @@ pub(crate) enum HeaderCmpResult {
// If they aren't equal, something is broken.
pub(super) const HEADER_MASK: u32 = 0xFFFE_0C00;
/// Compares the versions, layers, and sample rates of two frame headers.
///
/// It is safe to assume that the reader will no longer produce valid headers if [`HeaderCmpResult::Undetermined`]
/// is returned.
///
/// To compare two already constructed [`Header`]s, use [`Header::cmp()`].
///
/// ## Returns
///
/// - [`HeaderCmpResult::Equal`] if the headers are equal.
/// - [`HeaderCmpResult::NotEqual`] if the headers are not equal.
/// - [`HeaderCmpResult::Undetermined`] if the comparison could not be made (Some IO error occurred).
pub(crate) fn cmp_header<R>(
reader: &mut R,
header_size: u32,
@ -162,7 +210,7 @@ pub enum Emphasis {
CCIT_J17,
}
#[derive(Copy, Clone)]
#[derive(Copy, Clone, Debug)]
pub(crate) struct Header {
pub(crate) sample_rate: u32,
pub(crate) len: u32,
@ -269,14 +317,21 @@ impl Header {
Some(header)
}
/// Equivalent of [`cmp_header()`], but for an already constructed `Header`.
pub(super) fn cmp(self, other: &Self) -> bool {
self.version == other.version
&& self.layer == other.layer
&& self.sample_rate == other.sample_rate
}
}
pub(super) struct XingHeader {
pub(super) struct VbrHeader {
pub frames: u32,
pub size: u32,
}
impl XingHeader {
impl VbrHeader {
pub(super) fn read(reader: &mut &[u8]) -> Result<Option<Self>> {
let reader_len = reader.len();
@ -331,7 +386,9 @@ impl XingHeader {
#[cfg(test)]
mod tests {
use crate::config::ParsingMode;
use crate::tag::utils::test_utils::read_path;
use std::io::{Cursor, Read, Seek, SeekFrom};
#[test]
@ -347,21 +404,30 @@ mod tests {
}
#[test]
fn rev_search_for_frame_sync() {
fn test<R: Read + Seek>(reader: &mut R, expected_result: Option<u64>) {
#[rustfmt::skip]
fn rev_search_for_frame_header() {
fn test<R: Read + Seek>(reader: &mut R, expected_reader_position: Option<u64>) {
// We have to start these at the end to do a reverse search, of course :)
let mut pos = reader.seek(SeekFrom::End(0)).unwrap();
let ret = super::rev_search_for_frame_sync(reader, &mut pos).unwrap();
assert_eq!(ret, expected_result);
let ret = super::rev_search_for_frame_header(reader, &mut pos, ParsingMode::Strict);
if expected_reader_position.is_some() {
assert!(ret.is_ok());
assert!(ret.unwrap().is_some());
assert_eq!(Some(pos), expected_reader_position);
return;
}
assert!(ret.unwrap().is_none());
}
test(&mut Cursor::new([0xFF, 0xFB, 0x00]), Some(0));
test(&mut Cursor::new([0x00, 0x00, 0x01, 0xFF, 0xFB]), Some(3));
test(&mut Cursor::new([0xFF, 0xFB, 0x52, 0xC4]), Some(0));
test(&mut Cursor::new([0x00, 0x00, 0x01, 0xFF, 0xFB, 0x52, 0xC4]), Some(3));
test(&mut Cursor::new([0x01, 0xFF]), None);
let bytes = read_path("tests/files/assets/rev_frame_sync_search.mp3");
let mut reader = Cursor::new(bytes);
test(&mut reader, Some(283));
test(&mut reader, Some(595));
}
}

46
lofty/src/mpeg/properties.rs
View file

@ -1,14 +1,13 @@
use super::header::{ChannelMode, Emphasis, Header, Layer, MpegVersion, XingHeader};
use super::header::{ChannelMode, Emphasis, Header, Layer, MpegVersion, VbrHeader};
use crate::config::ParsingMode;
use crate::error::Result;
use crate::mpeg::header::{cmp_header, rev_search_for_frame_sync, HeaderCmpResult, HEADER_MASK};
use crate::mpeg::header::rev_search_for_frame_header;
use crate::properties::{ChannelMask, FileProperties};
use crate::util::math::RoundedDivision;
use std::io::{Read, Seek, SeekFrom};
use std::time::Duration;
use byteorder::{BigEndian, ReadBytesExt};
/// An MPEG file's audio properties
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[non_exhaustive]
@ -127,8 +126,9 @@ pub(super) fn read_properties<R>(
reader: &mut R,
first_frame: (Header, u64),
mut last_frame_offset: u64,
xing_header: Option<XingHeader>,
xing_header: Option<VbrHeader>,
file_length: u64,
parse_mode: ParsingMode,
) -> Result<()>
where
R: Read + Seek,
@ -177,29 +177,17 @@ where
reader.seek(SeekFrom::Start(last_frame_offset))?;
let mut last_frame = None;
let mut pos = reader.stream_position()?;
let mut pos = last_frame_offset;
while pos > 0 {
match rev_search_for_frame_sync(reader, &mut pos) {
// Found a frame sync, attempt to read a header
Ok(Some(_)) => {
match rev_search_for_frame_header(reader, &mut pos, parse_mode) {
// Found a frame header
Ok(Some(header)) => {
// Move `last_frame_offset` back to the actual position
last_frame_offset = reader.stream_position()?;
let last_frame_data = reader.read_u32::<BigEndian>()?;
last_frame_offset = pos;
if let Some(last_frame_header) = Header::read(last_frame_data) {
match cmp_header(
reader,
4,
last_frame_header.len,
last_frame_data,
HEADER_MASK,
) {
HeaderCmpResult::Equal | HeaderCmpResult::Undetermined => {
last_frame = Some(last_frame_header);
break;
},
HeaderCmpResult::NotEqual => {},
}
if header.cmp(&first_frame_header) {
last_frame = Some(header);
break;
}
},
// Encountered some IO error, just break
@ -211,11 +199,11 @@ where
if let Some(last_frame_header) = last_frame {
let stream_len = last_frame_offset - first_frame_offset + u64::from(last_frame_header.len);
let length = ((stream_len as f64) * 8.0) / f64::from(properties.audio_bitrate) + 0.5;
let length = (stream_len * 8).div_round(u64::from(properties.audio_bitrate));
if length > 0.0 {
properties.overall_bitrate = (((file_length as f64) * 8.0) / length) as u32;
properties.duration = Duration::from_millis(length as u64);
if length > 0 {
properties.overall_bitrate = ((file_length * 8) / length) as u32;
properties.duration = Duration::from_millis(length);
}
}

8
lofty/src/mpeg/read.rs
View file

@ -1,4 +1,4 @@
use super::header::{cmp_header, search_for_frame_sync, Header, HeaderCmpResult, XingHeader};
use super::header::{cmp_header, search_for_frame_sync, Header, HeaderCmpResult, VbrHeader};
use super::{MpegFile, MpegProperties};
use crate::ape::header::read_ape_header;
use crate::config::{ParseOptions, ParsingMode};
@ -6,6 +6,7 @@ use crate::error::Result;
use crate::id3::v2::header::Id3v2Header;
use crate::id3::v2::read::parse_id3v2;
use crate::id3::{find_id3v1, find_lyrics3v2, FindId3v2Config, ID3FindResults};
use crate::io::SeekStreamLen;
use crate::macros::{decode_err, err};
use crate::mpeg::header::HEADER_MASK;
@ -182,9 +183,9 @@ where
let mut xing_reader = [0; 32];
reader.read_exact(&mut xing_reader)?;
let xing_header = XingHeader::read(&mut &xing_reader[..])?;
let xing_header = VbrHeader::read(&mut &xing_reader[..])?;
let file_length = reader.seek(SeekFrom::End(0))?;
let file_length = reader.stream_len_hack()?;
super::properties::read_properties(
&mut file.properties,
@ -193,6 +194,7 @@ where
last_frame_offset,
xing_header,
file_length,
parse_options.parsing_mode,
)?;
}

6
lofty/src/properties/tests.rs
View file

@ -75,7 +75,7 @@ const MP1_PROPERTIES: MpegProperties = MpegProperties {
copyright: false,
original: true,
duration: Duration::from_millis(588), // FFmpeg reports 576, possibly an issue
overall_bitrate: 383, // TODO: FFmpeg reports 392
overall_bitrate: 384, // TODO: FFmpeg reports 392
audio_bitrate: 384,
sample_rate: 32000,
channels: 2,
@ -89,8 +89,8 @@ const MP2_PROPERTIES: MpegProperties = MpegProperties {
mode_extension: None,
copyright: false,
original: true,
duration: Duration::from_millis(1344), // TODO: FFmpeg reports 1440 here
overall_bitrate: 411, // FFmpeg reports 384, related to above issue
duration: Duration::from_millis(1440),
overall_bitrate: 384,
audio_bitrate: 384,
sample_rate: 48000,
channels: 2,