feat: add ogg postprocessor to downloader

Cargo.toml

@@ -11,7 +11,7 @@ categories = ["api-bindings", "multimedia"]
 include = ["/src", "README.md", "LICENSE", "!snapshots"]
 
 [workspace]
-members = [".", "codegen", "downloader", "cli"]
+members = [".", "codegen", "downloader", "postprocessor", "cli"]
 
 [features]
 default = ["default-tls"]

downloader/Cargo.toml

@@ -30,6 +30,7 @@ rustls-tls-native-roots = [
 
 [dependencies]
 rustypipe = { path = "..", default-features = false }
+rustypipe-postprocessor = { path = "../postprocessor" }
 once_cell = "1.12.0"
 regex = "1.6.0"
 thiserror = "1.0.36"

downloader/src/lib.rs

@@ -14,7 +14,7 @@ use rand::Rng;
 use regex::Regex;
 use reqwest::{header, Client};
 use rustypipe::{
-    model::{traits::FileFormat, AudioCodec, VideoCodec, VideoPlayer},
+    model::{traits::FileFormat, AudioCodec, AudioFormat, VideoCodec, VideoPlayer},
     param::StreamFilter,
 };
 use tokio::{
@@ -346,13 +346,34 @@ pub async fn download_video(
         // Downloading combined video/audio stream (no conversion)
         (Some(video), None) => {
             pb.set_message(format!("Downloading {title}"));
-            download_single_file(
-                &video.url,
-                download_dir.join(output_fname).with_extension(&format),
-                http,
-                pb.clone(),
-            )
-            .await?;
+            download_single_file(&video.url, output_path, http, pb.clone()).await?;
+        }
+        // Downloading audio only
+        (None, Some(audio)) => {
+            pb.set_message(format!("Downloading {title}"));
+
+            let (dl_path, postprocessor) = match (audio.format, audio.codec) {
+                (AudioFormat::M4a, AudioCodec::Mp4a) => (output_path.clone(), None),
+                (AudioFormat::Webm, AudioCodec::Opus) => (
+                    download_dir.join(format!(
+                        "{}.audio{}",
+                        output_fname,
+                        audio.format.extension()
+                    )),
+                    Some(AudioFormat::Webm),
+                ),
+                _ => (output_path.clone(), None),
+            };
+
+            download_single_file(&audio.url, &dl_path, http, pb.clone()).await?;
+
+            if let Some(postprocessor) = postprocessor {
+                pb.set_message(format!("Converting {title}"));
+                if postprocessor == AudioFormat::Webm {
+                    rustypipe_postprocessor::ogg_from_webm::process(&dl_path, &output_path)?;
+                }
+                fs::remove_file(&dl_path).await?;
+            }
         }
         // Downloading split video/audio streams (requires conversion with ffmpeg)
         _ => {

downloader/src/util.rs

@@ -20,6 +20,8 @@ pub enum DownloadError {
     Input(Cow<'static, str>),
     #[error("error: {0}")]
     Other(Cow<'static, str>),
+    #[error("Postprocessing error: {0}")]
+    Postprocessing(#[from] rustypipe_postprocessor::PostprocessingError),
 }
 
 /// Split an URL into its base string and parameter map

postprocessor/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "rustypipe-postprocessor"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+thiserror = "1.0.40"
+
+[dev-dependencies]
+path_macro = "1.0.0"
+once_cell = "1.12.0"
+temp_testdir = "0.2.3"

postprocessor/src/crc.rs

@@ -0,0 +1,75 @@
+// Ogg decoder and encoder written in Rust
+//
+// Original source: https://github.com/RustAudio/ogg
+//
+// Copyright (c) 2016-2017 est31 <MTest31@outlook.com>
+// and contributors. All rights reserved.
+// Redistribution or use only under the terms
+// specified in the LICENSE file attached to this
+// source distribution.
+
+/*!
+Implementation of the CRC algorithm with the
+vorbis specific parameters and setup
+*/
+
+// Lookup table to enable bytewise CRC32 calculation
+static CRC_LOOKUP_ARRAY: &[u32] = &lookup_array();
+
+const fn get_tbl_elem(idx: u32) -> u32 {
+    let mut r: u32 = idx << 24;
+    let mut i = 0;
+    while i < 8 {
+        r = (r << 1) ^ (-(((r >> 31) & 1) as i32) as u32 & 0x04c11db7);
+        i += 1;
+    }
+    r
+}
+
+const fn lookup_array() -> [u32; 0x100] {
+    let mut lup_arr: [u32; 0x100] = [0; 0x100];
+    let mut i = 0;
+    while i < 0x100 {
+        lup_arr[i] = get_tbl_elem(i as u32);
+        i += 1;
+    }
+    lup_arr
+}
+
+pub fn crc32(array: &[u8]) -> u32 {
+    crc32_update(0, array)
+}
+
+pub fn crc32_update(cur: u32, array: &[u8]) -> u32 {
+    let mut ret: u32 = cur;
+    for av in array {
+        ret = (ret << 8) ^ CRC_LOOKUP_ARRAY[(*av as u32 ^ (ret >> 24)) as usize];
+    }
+    ret
+}
+
+#[test]
+fn test_crc32() {
+    // Test page taken from real Ogg file
+    let test_arr = &[
+        0x4f, 0x67, 0x67, 0x53, 0x00, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x74,
+        0xa3, 0x90, 0x5b, 0x00, 0x00, 0x00, 0x00,
+        // The spec requires us to zero out the CRC field
+        /*0x6d, 0x94, 0x4e, 0x3d,*/
+        0x00, 0x00, 0x00, 0x00, 0x01, 0x1e, 0x01, 0x76, 0x6f, 0x72, 0x62, 0x69, 0x73, 0x00, 0x00,
+        0x00, 0x00, 0x02, 0x44, 0xac, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0xb5, 0x01, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0xb8, 0x01,
+    ];
+    println!();
+    println!(
+        "CRC of \"==!\" calculated as 0x{:08x} (expected 0x9f858776)",
+        crc32(&[61, 61, 33])
+    );
+    println!(
+        "Test page CRC calculated as 0x{:08x} (expected 0x3d4e946d)",
+        crc32(test_arr)
+    );
+    assert_eq!(crc32(&[61, 61, 33]), 0x9f858776);
+    assert_eq!(crc32(test_arr), 0x3d4e946d);
+    assert_eq!(crc32(&test_arr[0..27]), 0x7b374db8);
+}

postprocessor/src/lib.rs

@@ -0,0 +1,73 @@
+#![allow(dead_code)]
+
+pub mod ogg_from_webm;
+
+mod crc;
+mod ogg;
+mod webm;
+
+/// Error from the postprocessor
+#[derive(thiserror::Error, Debug)]
+#[non_exhaustive]
+pub enum PostprocessingError {
+    /// File IO error
+    #[error(transparent)]
+    Io(#[from] std::io::Error),
+    #[error("file format not recognized: {0}")]
+    InvalidFormat(&'static str),
+    #[error("no such element: expected {0:#x}, got {1:#x}")]
+    NoSuchElement(u32, u32),
+    #[error("bad element: {0}")]
+    BadElement(String),
+    #[error("invalid encoded length")]
+    InvalidLength,
+    #[error("invalid string")]
+    InvalidString,
+    #[error("unexpected element size")]
+    UnexpectedSize,
+    #[error("unsupported op: {0}")]
+    Unsupported(&'static str),
+    #[error("int conversion: {0}")]
+    Conversion(#[from] std::num::TryFromIntError),
+}
+
+pub(crate) type Result<T> = std::result::Result<T, PostprocessingError>;
+
+#[cfg(test)]
+pub(crate) mod tests {
+    use std::{
+        fs::File,
+        io::{BufReader, Read},
+        os::unix::prelude::MetadataExt,
+        path::{Path, PathBuf},
+    };
+
+    use once_cell::sync::Lazy;
+    use path_macro::path;
+
+    pub static TESTFILES: Lazy<PathBuf> = Lazy::new(|| {
+        path!(env!("CARGO_MANIFEST_DIR") / ".." / "testfiles")
+            .canonicalize()
+            .unwrap()
+    });
+
+    pub fn assert_files_eq<P: AsRef<Path>, P2: AsRef<Path>>(p1: P, p2: P2) {
+        let f1 = File::open(p1).unwrap();
+        let f2 = File::open(p2).unwrap();
+
+        let size = f1.metadata().unwrap().size();
+        assert_eq!(size, f2.metadata().unwrap().size(), "File sizes dont match");
+
+        let mut r1 = BufReader::new(f1);
+        let mut r2 = BufReader::new(f2);
+
+        for i in 0..size {
+            let mut b1 = [0; 1];
+            let mut b2 = [0; 1];
+            r1.read_exact(&mut b1).unwrap();
+            r2.read_exact(&mut b2).unwrap();
+
+            assert_eq!(b1[0], b2[0], "Byte {i} does not match");
+        }
+    }
+}

postprocessor/src/ogg.rs

@@ -0,0 +1,131 @@
+use crate::{crc, PostprocessingError, Result};
+
+pub struct OggWriter {
+    sequence_count: u32,
+    stream_id: u32,
+    packet_flag: u8,
+    segment_table: [u8; 255],
+    segment_table_size: u8,
+    pub segment_table_next_timestamp: u64,
+}
+
+pub const FLAG_UNSET: u8 = 0x00;
+pub const FLAG_FIRST: u8 = 0x02;
+pub const FLAG_LAST: u8 = 0x04;
+const HEADER_CHECKSUM_OFFSET: usize = 22;
+const HEADER_SIZE: usize = 27;
+pub const TIME_SCALE_NS: u64 = 1000000000;
+
+pub const METADATA_VORBIS: [u8; 15] = [
+    0x03, 0x76, 0x6f, 0x72, 0x62, 0x69, 0x73, // "vorbis" binary string
+    0x00, 0x00, 0x00, 0x00, // writing application string size (not present)
+    0x00, 0x00, 0x00, 0x00, // additional tags count (zero means no tags)
+];
+
+pub const METADATA_OPUS: [u8; 16] = [
+    0x4F, 0x70, 0x75, 0x73, 0x54, 0x61, 0x67, 0x73, // "OpusTags" binary string
+    0x00, 0x00, 0x00, 0x00, // writing application string size (not present)
+    0x00, 0x00, 0x00, 0x00, // additional tags count (zero means no tags)
+];
+
+impl OggWriter {
+    pub fn new() -> Self {
+        Self {
+            sequence_count: 0,
+            stream_id: 1,
+            packet_flag: FLAG_FIRST,
+            segment_table: [0; 255],
+            segment_table_size: 0,
+            segment_table_next_timestamp: TIME_SCALE_NS,
+        }
+    }
+
+    pub fn make_packet_header(&mut self, gran_pos: u64, page: &[u8], immediate: bool) -> Vec<u8> {
+        let mut header = Vec::new();
+        let mut length = HEADER_SIZE;
+
+        header.extend_from_slice(b"OggS");
+        header.push(0); // version
+        header.push(self.packet_flag); // type
+
+        header.extend_from_slice(&gran_pos.to_le_bytes()); // granulate position
+
+        header.extend_from_slice(&self.stream_id.to_le_bytes()); // bitstream serial number
+        header.extend_from_slice(&self.sequence_count.to_le_bytes()); // page sequence number
+        self.sequence_count += 1;
+
+        header.extend_from_slice(&[0, 0, 0, 0]); // page checksum
+
+        header.push(self.segment_table_size);
+        header.extend_from_slice(&self.segment_table[0..self.segment_table_size as usize]);
+
+        length += self.segment_table_size as usize;
+        self.clear_segment_table();
+
+        let checksum = crc::crc32(&header[0..length]);
+        let checksum = crc::crc32_update(checksum, page);
+        Self::header_put_checksum(&mut header, checksum);
+
+        if immediate {
+            self.segment_table_next_timestamp -= TIME_SCALE_NS;
+        }
+        header
+    }
+
+    fn header_put_checksum(header: &mut Vec<u8>, checksum: u32) {
+        let cs_bts = checksum.to_le_bytes();
+        let to_fill = (HEADER_CHECKSUM_OFFSET + cs_bts.len()).saturating_sub(header.len());
+        for _ in 0..to_fill {
+            header.push(0);
+        }
+        header[HEADER_CHECKSUM_OFFSET..(HEADER_CHECKSUM_OFFSET + cs_bts.len())]
+            .copy_from_slice(&cs_bts[..]);
+    }
+
+    pub fn clear_segment_table(&mut self) {
+        self.segment_table_next_timestamp += TIME_SCALE_NS;
+        self.packet_flag = FLAG_UNSET;
+        self.segment_table_size = 0;
+    }
+
+    pub fn add_packet_segment(&mut self, size: u32) -> Result<bool> {
+        if size > 65025 {
+            return Err(PostprocessingError::Unsupported(
+                "page size cannot be larger than 65025",
+            ));
+        }
+
+        let mut available =
+            (self.segment_table.len() as u32 - self.segment_table_size as u32) * 255;
+        let extra = (size % 255) == 0;
+
+        if extra {
+            // add a zero byte entry in the table
+            // required to indicate the sample size is multiple of 255
+            available -= 255;
+        }
+
+        // check if possible add the segment, without overflow the table
+        if available < size {
+            return Ok(false); // not enough space on the page
+        }
+
+        let mut seg = size;
+        while seg > 0 {
+            self.segment_table[self.segment_table_size as usize] = seg.min(255) as u8;
+            self.segment_table_size += 1;
+            seg = seg.saturating_sub(255);
+        }
+
+        if extra {
+            self.segment_table[self.segment_table_size as usize] = 0;
+            self.segment_table_size += 1;
+        }
+
+        Ok(true)
+    }
+
+    pub fn set_packet_flag(&mut self, flag: u8) {
+        self.packet_flag = flag;
+    }
+}

postprocessor/src/ogg_from_webm.rs

@@ -0,0 +1,179 @@
+use std::{
+    fs::File,
+    io::{BufWriter, Read, Write},
+    path::Path,
+};
+
+use crate::{
+    ogg::{OggWriter, FLAG_LAST, METADATA_OPUS, METADATA_VORBIS, TIME_SCALE_NS},
+    webm::{TrackKind, WebmReader},
+    PostprocessingError,
+};
+
+pub fn test(mut source: impl Read) -> Result<bool, PostprocessingError> {
+    let mut buf = [0; 4];
+    source.read_exact(&mut buf)?;
+
+    match u32::from_be_bytes(buf) {
+        0x1a45dfa3 => Ok(true),  // webm/mkv
+        0x4f676753 => Ok(false), // ogg
+        _ => Err(PostprocessingError::InvalidFormat("unknown magic number")),
+    }
+}
+
+pub fn process<P: AsRef<Path>, P2: AsRef<Path>>(
+    source: P,
+    dest: P2,
+) -> Result<(), PostprocessingError> {
+    let mut webm = WebmReader::new(File::open(source)?)?;
+    webm.parse()?;
+    if !webm.get_next_segment()? {
+        return Err(PostprocessingError::InvalidFormat("no segment"));
+    }
+
+    let mut ogg = OggWriter::new();
+    let mut output = BufWriter::new(File::create(dest)?);
+
+    // Select track
+    let track = match &webm.tracks {
+        Some(tracks) => {
+            let track_id = tracks
+                .iter()
+                .enumerate()
+                .find(|(_, track)| {
+                    track.kind == TrackKind::Audio
+                        && (track.codec_id == "A_OPUS" || track.codec_id == "A_VORBIS")
+                })
+                .ok_or(PostprocessingError::InvalidFormat("no audio tracks"))?
+                .0;
+            webm.select_track(track_id).unwrap().clone()
+        }
+        None => return Err(PostprocessingError::InvalidFormat("no tracks")),
+    };
+
+    // Get sample rate
+    let res = get_sample_freq_from_track(&track.b_metadata);
+
+    // Create packet with codec init data
+    if !track.codec_private.is_empty() {
+        ogg.add_packet_segment(track.codec_private.len().try_into()?)?;
+        let header = ogg.make_packet_header(0, &track.codec_private, true);
+        output.write_all(&header)?;
+        output.write_all(&track.codec_private)?;
+    }
+
+    // Create packet with metadata
+    let metadata = match track.codec_id.as_str() {
+        "A_OPUS" => METADATA_OPUS.as_slice(),
+        "A_VORBIS" => METADATA_VORBIS.as_slice(),
+        _ => unreachable!(),
+    };
+    ogg.add_packet_segment(metadata.len().try_into()?)?;
+    let header = ogg.make_packet_header(0, metadata, true);
+    output.write_all(&header)?;
+    output.write_all(metadata)?;
+
+    // Calculate amount of packets
+    let mut page = Vec::new();
+    let mut webm_block = None;
+    while !webm.is_done() {
+        let block = match webm_block {
+            Some(block) => {
+                webm_block = None;
+                Some(block)
+            }
+            None => webm.get_next_block()?,
+        };
+
+        if let Some(block) = block {
+            let timestamp = block.absolute_time_code_ns + track.codec_delay;
+            let added = if timestamp >= ogg.segment_table_next_timestamp {
+                false
+            } else {
+                ogg.add_packet_segment(block.data_size.try_into()?)?
+            };
+
+            if added {
+                webm.get_block_data(&block, &mut page)?;
+                continue;
+            }
+        }
+
+        let mut elapsed_ns = track.codec_delay;
+        match block {
+            Some(block) => {
+                elapsed_ns += block.absolute_time_code_ns;
+            }
+            None => {
+                // TODO: move to ogg
+                ogg.set_packet_flag(FLAG_LAST);
+                elapsed_ns += webm.webm_block_last_timecode();
+
+                if track.default_duration > 0 {
+                    elapsed_ns += track.default_duration;
+                } else {
+                    elapsed_ns += webm.webm_block_near_duration();
+                }
+            }
+        }
+
+        // get the sample count in the page
+        let sample_count: f64 = (elapsed_ns as f64 / TIME_SCALE_NS as f64) * res as f64;
+        let sample_count = sample_count.ceil() as u64;
+
+        let header = ogg.make_packet_header(sample_count, &page, false);
+
+        // dump data
+        output.write_all(&header)?;
+        output.write_all(&page)?;
+
+        page = Vec::new();
+        webm_block = block;
+    }
+
+    output.flush()?;
+    Ok(())
+}
+
+fn get_sample_freq_from_track(b_metadata: &[u8]) -> f32 {
+    let mut i = 0;
+    while i < b_metadata.len().saturating_sub(5) {
+        let id_bts: [u8; 2] = b_metadata[i..i + 2].try_into().unwrap();
+        let id = u16::from_be_bytes(id_bts);
+
+        if id == 0xB584 {
+            let freq_bts: [u8; 4] = b_metadata[i + 2..i + 6].try_into().unwrap();
+            return f32::from_be_bytes(freq_bts);
+        }
+        i += 2;
+    }
+    0.0
+}
+
+#[cfg(test)]
+mod tests {
+    use path_macro::path;
+
+    use crate::tests::{assert_files_eq, TESTFILES};
+
+    use super::*;
+
+    #[test]
+    fn t_test() {
+        let path = path!(*TESTFILES / "postprocessor" / "audio1.webm");
+        let mut file = File::open(&path).unwrap();
+        assert!(test(&mut file).unwrap());
+    }
+
+    #[test]
+    fn t_process() {
+        let temp = temp_testdir::TempDir::default();
+
+        let source = path!(*TESTFILES / "postprocessor" / "audio1.webm");
+        let dest = path!(temp / "audio1.ogg");
+        let expect = path!(*TESTFILES / "postprocessor" / "conv" / "audio1.ogg");
+
+        process(&source, &dest).unwrap();
+        assert_files_eq(&dest, &expect);
+    }
+}

postprocessor/src/webm.rs

@@ -0,0 +1,736 @@
+use std::{
+    fs::File,
+    io::{BufReader, Read, Seek, SeekFrom},
+    os::unix::prelude::MetadataExt,
+};
+
+use crate::{PostprocessingError, Result};
+
+#[derive(Debug)]
+pub struct WebmReader {
+    stream: BufReader<File>,
+    len: u64,
+    segment: Option<Segment>,
+    cluster: Option<Cluster>,
+    pub tracks: Option<Vec<WebmTrack>>,
+    selected_track: Option<usize>,
+    done: bool,
+    first_segment: bool,
+    webm_block_near_duration: u64,
+    webm_block_last_timecode: u64,
+}
+
+#[derive(Debug, Copy, Clone)]
+struct Element {
+    typ: u32,
+    offset: u64,
+    content_size: u64,
+    size: u64,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Info {
+    pub timecode_scale: u64,
+    pub duration: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct WebmTrack {
+    pub track_number: u64,
+    track_type: u32,
+    pub codec_id: String,
+    pub codec_private: Vec<u8>,
+    pub b_metadata: Vec<u8>,
+    pub kind: TrackKind,
+    pub default_duration: u64,
+    pub codec_delay: u64,
+    pub seek_pre_roll: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct Segment {
+    pub info: Option<Info>,
+    tracks: Option<Vec<WebmTrack>>,
+    current_cluster: Option<Element>,
+    rf: Element,
+    first_cluster_in_segment: bool,
+}
+
+impl Segment {
+    fn new(rf: Element) -> Segment {
+        Segment {
+            info: None,
+            tracks: None,
+            current_cluster: None,
+            rf,
+            first_cluster_in_segment: true,
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct SimpleBlock {
+    pub created_from_block: bool,
+    pub track_number: u64,
+    pub relative_time_code: u16,
+    pub absolute_time_code_ns: u64,
+    pub flags: u8,
+    pub offset: u64,
+    pub data_size: u64,
+    rf: Element,
+}
+
+impl SimpleBlock {
+    fn new(rf: Element) -> Self {
+        Self {
+            created_from_block: false,
+            track_number: 0,
+            relative_time_code: 0,
+            absolute_time_code_ns: 0,
+            flags: 0,
+            offset: 0,
+            data_size: 0,
+            rf,
+        }
+    }
+
+    pub fn is_keyframe(&self) -> bool {
+        (self.flags & 0x80) == 0x80
+    }
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct Cluster {
+    rf: Element,
+    current_simple_block: Option<SimpleBlock>,
+    current_block_group: Option<Element>,
+    timecode: u64,
+}
+
+impl Cluster {
+    fn new(rf: Element) -> Self {
+        Self {
+            rf,
+            current_simple_block: None,
+            current_block_group: None,
+            timecode: 0,
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum TrackKind {
+    Audio,
+    Video,
+    Other,
+}
+
+const ID_EMBL: u32 = 0x0A45DFA3;
+const ID_EMBL_READ_VERSION: u32 = 0x02F7;
+const ID_EMBL_DOC_TYPE: u32 = 0x0282;
+const ID_EMBL_DOC_TYPE_READ_VERSION: u32 = 0x0285;
+const ID_SEGMENT: u32 = 0x08538067;
+const ID_INFO: u32 = 0x0549A966;
+const ID_TIMECODE_SCALE: u32 = 0x0AD7B1;
+const ID_DURATION: u32 = 0x489;
+const ID_TRACKS: u32 = 0x0654AE6B;
+const ID_TRACK_ENTRY: u32 = 0x2E;
+const ID_TRACK_NUMBER: u32 = 0x57;
+const ID_TRACK_TYPE: u32 = 0x03;
+const ID_CODEC_ID: u32 = 0x06;
+const ID_CODEC_PRIVATE: u32 = 0x23A2;
+const ID_VIDEO: u32 = 0x60;
+const ID_AUDIO: u32 = 0x61;
+const ID_DEFAULT_DURATION: u32 = 0x3E383;
+const ID_FLAG_LACING: u32 = 0x1C;
+const ID_CODEC_DELAY: u32 = 0x16AA;
+const ID_SEEK_PRE_ROLL: u32 = 0x16BB;
+const ID_CLUSTER: u32 = 0x0F43B675;
+const ID_TIMECODE: u32 = 0x67;
+const ID_SIMPLE_BLOCK: u32 = 0x23;
+const ID_BLOCK: u32 = 0x21;
+const ID_GROUP_BLOCK: u32 = 0x20;
+
+impl WebmReader {
+    pub fn new(file: File) -> Result<Self> {
+        let md = file.metadata()?;
+        Ok(Self {
+            stream: BufReader::new(file),
+            len: md.size(),
+            segment: None,
+            cluster: None,
+            tracks: None,
+            selected_track: None,
+            done: false,
+            first_segment: false,
+            webm_block_near_duration: 0,
+            webm_block_last_timecode: 0,
+        })
+    }
+
+    /// Make sure the parser did not go beyond the current element and
+    /// skip to the start if the next element.
+    fn ensure(&mut self, rf: &Element) -> Result<()> {
+        let pos = self.stream.stream_position()?;
+        let elem_end = rf.offset + rf.size;
+
+        if pos > elem_end {
+            return Err(PostprocessingError::Io(std::io::Error::new(
+                std::io::ErrorKind::UnexpectedEof,
+                format!(
+                    "parser go beyond limits of the Element. type={} offset={} size={} position={}",
+                    rf.typ, rf.offset, rf.size, pos,
+                ),
+            )));
+        }
+
+        self.stream.seek(SeekFrom::Start(elem_end))?;
+        Ok(())
+    }
+
+    fn read_byte(&mut self) -> Result<u8> {
+        let mut bt = [0; 1];
+        self.stream.read_exact(&mut bt)?;
+        Ok(bt[0])
+    }
+
+    fn read_u16(&mut self) -> Result<u16> {
+        let mut bt = [0; 2];
+        self.stream.read_exact(&mut bt)?;
+        Ok(u16::from_be_bytes(bt))
+    }
+
+    fn read_number(&mut self, parent: &Element) -> Result<u64> {
+        let mut value: u64 = 0;
+        for _ in 0..parent.content_size {
+            let rd = self.read_byte()?;
+            value = (value << 8) | u64::from(rd);
+        }
+        Ok(value)
+    }
+
+    fn read_string(&mut self, parent: &Element) -> Result<String> {
+        String::from_utf8(self.read_blob(parent)?).map_err(|_| PostprocessingError::InvalidString)
+    }
+
+    fn read_blob(&mut self, parent: &Element) -> Result<Vec<u8>> {
+        let length = parent.content_size as usize;
+        let mut buf = vec![0u8; length];
+        self.stream.read_exact(&mut buf)?;
+        Ok(buf)
+    }
+
+    fn read_encoded_number(&mut self) -> Result<u64> {
+        let mut value = u64::from(self.read_byte()?);
+
+        if value > 0 {
+            let mut mask: u64 = 0x80;
+
+            for size in 1..9 {
+                if (value & mask) == mask {
+                    mask = 0xff;
+                    mask >>= size;
+
+                    let mut number = value & mask;
+
+                    for _ in 1..size {
+                        value = u64::from(self.read_byte()?);
+                        number = (number << 8) | value;
+                    }
+                    return Ok(number);
+                }
+
+                mask >>= 1;
+            }
+        }
+        Err(PostprocessingError::InvalidLength)
+    }
+
+    fn read_element(&mut self) -> Result<Element> {
+        let offset = self.stream.stream_position()?;
+        let typ = self.read_encoded_number()? as u32;
+        let content_size = self.read_encoded_number()?;
+        let size = content_size + self.stream.stream_position()? - offset;
+
+        Ok(Element {
+            typ,
+            offset,
+            content_size,
+            size,
+        })
+    }
+
+    fn read_element_expected(&mut self, expected: u32) -> Result<Element> {
+        let elem = self.read_element()?;
+        if expected != 0 && elem.typ != expected {
+            return Err(PostprocessingError::NoSuchElement(expected, elem.typ));
+        }
+        Ok(elem)
+    }
+
+    fn until_element(&mut self, rf: Option<&Element>, expected: &[u32]) -> Result<Option<Element>> {
+        loop {
+            let brk = match rf {
+                Some(rf) => self.stream.stream_position()? >= (rf.offset + rf.size),
+                None => self.stream.stream_position()? >= self.len,
+            };
+            if brk {
+                break;
+            }
+
+            let elem = self.read_element()?;
+            if expected.is_empty() {
+                return Ok(Some(elem));
+            }
+            for t in expected {
+                if &elem.typ == t {
+                    return Ok(Some(elem));
+                }
+            }
+            self.ensure(&elem)?;
+        }
+        Ok(None)
+    }
+
+    fn read_ebml(
+        &mut self,
+        rf: &Element,
+        min_read_version: u64,
+        min_doc_type_version: u64,
+    ) -> Result<bool> {
+        let elem_v = self.until_element(Some(rf), &[ID_EMBL_READ_VERSION])?;
+        match elem_v {
+            Some(elem_v) => {
+                if self.read_number(&elem_v)? > min_read_version {
+                    return Ok(false);
+                }
+
+                let elem_t = self.until_element(Some(rf), &[ID_EMBL_DOC_TYPE])?;
+                match elem_t {
+                    Some(elem_t) => {
+                        if self.read_string(&elem_t)? != "webm" {
+                            return Ok(false);
+                        }
+
+                        let elem_tv =
+                            self.until_element(Some(rf), &[ID_EMBL_DOC_TYPE_READ_VERSION])?;
+                        match elem_tv {
+                            Some(elem_tv) => {
+                                Ok(self.read_number(&elem_tv)? <= min_doc_type_version)
+                            }
+                            None => Ok(false),
+                        }
+                    }
+                    None => Ok(false),
+                }
+            }
+            None => Ok(false),
+        }
+    }
+
+    fn read_info(&mut self, rf: &Element) -> Result<Info> {
+        let mut info = Info {
+            timecode_scale: 0,
+            duration: 0,
+        };
+
+        while let Some(elem) = self.until_element(Some(rf), &[ID_TIMECODE_SCALE, ID_DURATION])? {
+            match elem.typ {
+                ID_TIMECODE_SCALE => {
+                    info.timecode_scale = self.read_number(&elem)?;
+                }
+                ID_DURATION => {
+                    info.duration = self.read_number(&elem)?;
+                }
+                _ => {}
+            }
+            self.ensure(&elem)?;
+        }
+
+        if info.timecode_scale == 0 {
+            return Err(PostprocessingError::BadElement(
+                "Element Timecode not found".to_owned(),
+            ));
+        }
+        Ok(info)
+    }
+
+    fn read_segment(
+        &mut self,
+        rf: Element,
+        track_lacing_expected: u64,
+        metadata_expected: bool,
+    ) -> Result<Segment> {
+        let mut seg = Segment::new(rf);
+        while let Some(elem) = self.until_element(Some(&rf), &[ID_INFO, ID_TRACKS, ID_CLUSTER])? {
+            match elem.typ {
+                ID_CLUSTER => {
+                    seg.current_cluster = Some(elem);
+                    break;
+                }
+                ID_INFO => {
+                    seg.info = Some(self.read_info(&elem)?);
+                    self.ensure(&elem)?;
+                }
+                ID_TRACKS => {
+                    seg.tracks = Some(self.read_tracks(&elem, track_lacing_expected)?);
+                    self.ensure(&elem)?;
+                }
+                _ => {}
+            }
+        }
+
+        if metadata_expected && (seg.info.is_none() || seg.tracks.is_none()) {
+            return Err(PostprocessingError::BadElement(format!(
+                "Cluster element found without Info and/or Tracks element at position {}",
+                rf.offset
+            )));
+        }
+        Ok(seg)
+    }
+
+    fn read_tracks(&mut self, rf: &Element, lacing_expected: u64) -> Result<Vec<WebmTrack>> {
+        let mut tracks = Vec::new();
+
+        while let Some(elem_te) = self.until_element(Some(rf), &[ID_TRACK_ENTRY])? {
+            let mut entry = WebmTrack {
+                track_number: 0,
+                track_type: 0,
+                codec_id: String::new(),
+                codec_private: Vec::new(),
+                b_metadata: Vec::new(),
+                kind: TrackKind::Other,
+                default_duration: 0,
+                codec_delay: 0,
+                seek_pre_roll: 0,
+            };
+            let mut drop = false;
+
+            while let Some(elem) = self.until_element(Some(&elem_te), &[])? {
+                match elem.typ {
+                    ID_TRACK_NUMBER => {
+                        entry.track_number = self.read_number(&elem)?;
+                    }
+                    ID_TRACK_TYPE => {
+                        entry.track_type = self.read_number(&elem)? as u32;
+                    }
+                    ID_CODEC_ID => {
+                        entry.codec_id = self.read_string(&elem)?;
+                    }
+                    ID_CODEC_PRIVATE => {
+                        entry.codec_private = self.read_blob(&elem)?;
+                    }
+                    ID_AUDIO | ID_VIDEO => {
+                        entry.b_metadata = self.read_blob(&elem)?;
+                    }
+                    ID_DEFAULT_DURATION => {
+                        entry.default_duration = self.read_number(&elem)?;
+                    }
+                    ID_FLAG_LACING => {
+                        drop = self.read_number(&elem)? != lacing_expected;
+                    }
+                    ID_CODEC_DELAY => {
+                        entry.codec_delay = self.read_number(&elem)?;
+                    }
+                    ID_SEEK_PRE_ROLL => {
+                        entry.seek_pre_roll = self.read_number(&elem)?;
+                    }
+                    _ => {}
+                }
+                self.ensure(&elem)?;
+            }
+            entry.kind = match entry.track_type {
+                1 => TrackKind::Video,
+                2 => TrackKind::Audio,
+                _ => TrackKind::Other,
+            };
+            if !drop {
+                tracks.push(entry);
+            }
+            self.ensure(&elem_te)?;
+        }
+        Ok(tracks)
+    }
+
+    fn read_simple_block(&mut self, rf: Element) -> Result<SimpleBlock> {
+        let mut sb = SimpleBlock::new(rf);
+        sb.track_number = self.read_encoded_number()?;
+        sb.relative_time_code = self.read_u16()?;
+        sb.flags = self.read_byte()?;
+        let pos = self.stream.stream_position()?;
+        sb.data_size = (rf.offset + rf.size)
+            .checked_sub(pos)
+            .ok_or(PostprocessingError::UnexpectedSize)?;
+        sb.offset = pos;
+        sb.created_from_block = rf.typ == ID_BLOCK;
+        Ok(sb)
+    }
+
+    fn read_cluster(&mut self, rf: Element) -> Result<Cluster> {
+        let elem = self.until_element(Some(&rf), &[ID_TIMECODE])?;
+        let mut cl = Cluster::new(rf);
+
+        match elem {
+            Some(elem) => {
+                cl.timecode = self.read_number(&elem)?;
+            }
+            None => {
+                return Err(PostprocessingError::BadElement(format!(
+                    "Cluster at {} without Timecode element",
+                    rf.offset
+                )))
+            }
+        }
+        Ok(cl)
+    }
+
+    fn inside_cluster_bounds(&mut self, cluster: &Cluster) -> Result<bool> {
+        Ok(self.stream.stream_position()? >= (cluster.rf.offset + cluster.rf.size))
+    }
+
+    pub fn get_next_cluster(&mut self) -> Result<Option<Cluster>> {
+        if self.done {
+            return Ok(None);
+        }
+
+        let (rf, cc) = if let Some(segment) = &mut self.segment {
+            if let Some(current_cluster) = segment.current_cluster {
+                if segment.first_cluster_in_segment {
+                    segment.first_cluster_in_segment = false;
+                    return Ok(Some(self.read_cluster(current_cluster)?));
+                }
+                (segment.rf, current_cluster)
+            } else {
+                return Ok(None);
+            }
+        } else {
+            return Ok(None);
+        };
+        self.ensure(&cc)?;
+
+        let elem = self.until_element(Some(&rf), &[ID_CLUSTER])?;
+        match elem {
+            Some(elem) => {
+                self.segment.as_mut().unwrap().current_cluster = Some(elem);
+                Ok(Some(self.read_cluster(elem)?))
+            }
+            None => Ok(None),
+        }
+    }
+
+    pub fn get_next_simple_block(&mut self, cluster: &mut Cluster) -> Result<Option<SimpleBlock>> {
+        if self.inside_cluster_bounds(cluster)? {
+            return Ok(None);
+        }
+
+        if let Some(current_block_group) = &cluster.current_block_group {
+            self.ensure(current_block_group)?;
+            cluster.current_block_group = None;
+            cluster.current_simple_block = None;
+        } else if let Some(current_simple_block) = &cluster.current_simple_block {
+            self.ensure(&current_simple_block.rf)?;
+        }
+
+        while !self.inside_cluster_bounds(cluster)? {
+            let elem = self.until_element(Some(&cluster.rf), &[ID_SIMPLE_BLOCK, ID_GROUP_BLOCK])?;
+            let nelem = match elem {
+                Some(elem) => {
+                    if elem.typ == ID_GROUP_BLOCK {
+                        cluster.current_block_group = Some(elem);
+                        let block_elem = self.until_element(Some(&elem), &[ID_BLOCK])?;
+
+                        match block_elem {
+                            Some(block_elem) => block_elem,
+                            None => {
+                                self.ensure(&elem)?;
+                                cluster.current_block_group = None;
+                                continue;
+                            }
+                        }
+                    } else {
+                        elem
+                    }
+                }
+                None => return Ok(None),
+            };
+
+            let mut csb = self.read_simple_block(nelem)?;
+
+            if self
+                .selected_track()
+                .map(|st| st.track_number == csb.track_number)
+                .unwrap_or_default()
+            {
+                csb.absolute_time_code_ns = (u64::from(csb.relative_time_code) + cluster.timecode)
+                    * self
+                        .segment
+                        .as_ref()
+                        .and_then(|seg| seg.info)
+                        .map(|inf| inf.timecode_scale)
+                        .unwrap_or(1);
+
+                cluster.current_simple_block = Some(csb);
+                return Ok(Some(csb));
+            }
+
+            cluster.current_simple_block = Some(csb);
+            self.ensure(&nelem)?;
+        }
+        Ok(None)
+    }
+
+    pub fn get_next_block(&mut self) -> Result<Option<SimpleBlock>> {
+        if self.segment.is_none() && !self.get_next_segment()? {
+            return Ok(None);
+        }
+
+        if self.cluster.is_none() {
+            self.cluster = self.get_next_cluster()?;
+            if self.cluster.is_none() {
+                self.segment = None;
+                return self.get_next_block();
+            }
+        }
+
+        let mut c = self.cluster.unwrap();
+        let res = self.get_next_simple_block(&mut c)?;
+        self.cluster = Some(c);
+
+        match res {
+            Some(res) => {
+                self.webm_block_near_duration =
+                    res.absolute_time_code_ns - self.webm_block_last_timecode;
+                self.webm_block_last_timecode = res.absolute_time_code_ns;
+                Ok(Some(res))
+            }
+            None => {
+                self.cluster = None;
+                self.get_next_block()
+            }
+        }
+    }
+
+    pub fn selected_track(&self) -> Option<&WebmTrack> {
+        if let (Some(tracks), Some(st)) = (&self.tracks, self.selected_track) {
+            return tracks.get(st);
+        }
+        None
+    }
+
+    pub fn select_track(&mut self, index: usize) -> Option<&WebmTrack> {
+        if let Some(tracks) = &self.tracks {
+            match tracks.get(index) {
+                Some(track) => {
+                    self.selected_track = Some(index);
+                    Some(track)
+                }
+                None => None,
+            }
+        } else {
+            None
+        }
+    }
+
+    pub fn parse(&mut self) -> Result<()> {
+        let elem_ebml = self.read_element_expected(ID_EMBL)?;
+        if !self.read_ebml(&elem_ebml, 1, 2)? {
+            return Err(PostprocessingError::InvalidFormat(
+                "Unsupported EBML data (WebM)",
+            ));
+        }
+        self.ensure(&elem_ebml)?;
+
+        let elem_seg = self.until_element(None, &[ID_SEGMENT])?;
+        match elem_seg {
+            Some(elem_seg) => {
+                let seg = self.read_segment(elem_seg, 0, true)?;
+                // TODO: avoid this clone
+                self.tracks = seg.tracks.clone();
+                self.segment = Some(seg);
+                self.selected_track = None;
+                self.done = false;
+                self.first_segment = true;
+
+                Ok(())
+            }
+            None => Err(PostprocessingError::InvalidFormat(
+                "Fragment element not found",
+            )),
+        }
+    }
+
+    pub fn get_next_segment(&mut self) -> Result<bool> {
+        if self.done {
+            return Ok(false);
+        }
+
+        if let Some(segment) = &self.segment {
+            if self.first_segment {
+                self.first_segment = false;
+                return Ok(true);
+            }
+            let srf = segment.rf;
+            self.ensure(&srf)?;
+        }
+
+        let elem = self.until_element(None, &[ID_SEGMENT])?;
+        match elem {
+            Some(elem) => {
+                self.segment = Some(self.read_segment(elem, 0, false)?);
+                Ok(true)
+            }
+            None => {
+                self.done = true;
+                Ok(false)
+            }
+        }
+    }
+
+    pub fn is_done(&self) -> bool {
+        self.done
+    }
+
+    pub fn webm_block_near_duration(&self) -> u64 {
+        self.webm_block_near_duration
+    }
+
+    pub fn webm_block_last_timecode(&self) -> u64 {
+        self.webm_block_last_timecode
+    }
+
+    pub fn get_block_data(&mut self, block: &SimpleBlock, bytes: &mut Vec<u8>) -> Result<()> {
+        let old_pos = self.stream.stream_position()?;
+        self.stream.seek(SeekFrom::Start(block.offset))?;
+
+        for _ in 0..block.data_size {
+            let mut bt = [0; 1];
+            self.stream.read_exact(&mut bt)?;
+            bytes.push(bt[0]);
+        }
+
+        self.stream.seek(SeekFrom::Start(old_pos))?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use path_macro::path;
+
+    use crate::tests::TESTFILES;
+
+    use super::*;
+
+    #[test]
+    fn read() {
+        let path = path!(*TESTFILES / "postprocessor" / "audio1.webm");
+        let file = File::open(&path).unwrap();
+        let mut reader = WebmReader::new(file).unwrap();
+        reader.parse().unwrap();
+        reader.get_next_segment().unwrap();
+        // TODO: check types
+        reader.select_track(0).unwrap();
+
+        dbg!(&reader);
+    }
+}

testfiles/postprocessor/LICENSE.md

@@ -0,0 +1,14 @@
+### `audio1`
+
+This test file was downloaded from the [EffectsLibrary](https://www.youtube.com/@EffectsLibrary)
+channel on YouTube
+
+**Title:** Pen Clicking & Scribbling Sound Effects
+
+**Source:** https://www.youtube.com/watch?v=cOtkrqo9Pjk
+
+**License:** Creative Commons Attribution 3.0
+
+This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of
+this license, visit http://creativecommons.org/licenses/by/3.0/ or send a letter to Creative
+Commons, PO Box 1866, Mountain View, CA 94042, USA.