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#[cfg(test)]
mod ogg_writer_test;
use std::io::{BufWriter, Write};
use byteorder::{LittleEndian, WriteBytesExt};
use bytes::Bytes;
use rtp::packetizer::Depacketizer;
use crate::io::Writer;
use crate::io::ogg_reader::*;
use shared::error::Result;
/// OggWriter is used to take RTP packets and write them to an OGG on disk
pub struct OggWriter<W: Write> {
writer: W,
sample_rate: u32,
channel_count: u8,
serial: u32,
page_index: u32,
checksum_table: [u32; 256],
previous_granule_position: u64,
previous_timestamp: u32,
last_payload_size: usize,
last_payload: Bytes,
}
impl<W: Write> OggWriter<W> {
/// new initialize a new OGG Opus writer with an io.Writer output
pub fn new(writer: W, sample_rate: u32, channel_count: u8) -> Result<Self> {
let mut w = OggWriter {
writer,
sample_rate,
channel_count,
serial: rand::random::<u32>(),
page_index: 0,
checksum_table: generate_checksum_table(),
// Timestamp and Granule MUST start from 1
// Only headers can have 0 values
previous_timestamp: 1,
previous_granule_position: 1,
last_payload_size: 0,
last_payload: Bytes::new(),
};
w.write_headers()?;
Ok(w)
}
/*
ref: https://tools.ietf.org/html/rfc7845.html
https://git.xiph.org/?p=opus-tools.git;a=blob;f=src/opus_header.c#l219
Page 0 Pages 1 ... n Pages (n+1) ...
+------------+ +---+ +---+ ... +---+ +-----------+ +---------+ +--
| | | | | | | | | | | | |
|+----------+| |+-----------------+| |+-------------------+ +-----
|||ID Header|| || Comment Header || ||Audio Data Packet 1| | ...
|+----------+| |+-----------------+| |+-------------------+ +-----
| | | | | | | | | | | | |
+------------+ +---+ +---+ ... +---+ +-----------+ +---------+ +--
^ ^ ^
| | |
| | Mandatory Page Break
| |
| ID header is contained on a single page
|
'Beginning Of Stream'
Figure 1: Example Packet Organization for a Logical Ogg Opus Stream
*/
fn write_headers(&mut self) -> Result<()> {
// ID Header
let mut ogg_id_header = Vec::with_capacity(19);
{
let mut header_writer = BufWriter::new(&mut ogg_id_header);
header_writer.write_all(ID_PAGE_SIGNATURE)?; // Magic Signature 'OpusHead'
header_writer.write_u8(1)?; // Version //8
header_writer.write_u8(self.channel_count)?; // Channel count //9
header_writer.write_u16::<LittleEndian>(DEFAULT_PRE_SKIP)?; // pre-skip //10-11
header_writer.write_u32::<LittleEndian>(self.sample_rate)?; // original sample rate, any valid sample e.g 48000, //12-15
header_writer.write_u16::<LittleEndian>(0)?; // output gain // 16-17
header_writer.write_u8(0)?; // channel map 0 = one stream: mono or stereo, //18
}
// Reference: https://tools.ietf.org/html/rfc7845.html#page-6
// RFC specifies that the ID Header page should have a granule position of 0 and a Header Type set to 2 (StartOfStream)
self.write_page(
&Bytes::from(ogg_id_header),
PAGE_HEADER_TYPE_BEGINNING_OF_STREAM,
0,
self.page_index,
)?;
self.page_index += 1;
// Comment Header
let mut ogg_comment_header = Vec::with_capacity(25);
{
let mut header_writer = BufWriter::new(&mut ogg_comment_header);
header_writer.write_all(COMMENT_PAGE_SIGNATURE)?; // Magic Signature 'OpusTags' //0-7
header_writer.write_u32::<LittleEndian>(10)?; // Vendor Length //8-11
header_writer.write_all(b"WebRTC.rs")?; // Vendor name 'WebRTC.rs' //12-20
header_writer.write_u32::<LittleEndian>(0)?; // User Comment List Length //21-24
}
// RFC specifies that the page where the CommentHeader completes should have a granule position of 0
self.write_page(
&Bytes::from(ogg_comment_header),
PAGE_HEADER_TYPE_CONTINUATION_OF_STREAM,
0,
self.page_index,
)?;
self.page_index += 1;
Ok(())
}
fn write_page(
&mut self,
payload: &Bytes,
header_type: u8,
granule_pos: u64,
page_index: u32,
) -> Result<()> {
self.last_payload_size = payload.len();
self.last_payload = payload.clone();
let n_segments = self.last_payload_size.div_ceil(255);
let mut page =
Vec::with_capacity(PAGE_HEADER_SIZE + 1 + self.last_payload_size + n_segments);
{
let mut header_writer = BufWriter::new(&mut page);
header_writer.write_all(PAGE_HEADER_SIGNATURE)?; // page headers starts with 'OggS'//0-3
header_writer.write_u8(0)?; // Version//4
header_writer.write_u8(header_type)?; // 1 = continuation, 2 = beginning of stream, 4 = end of stream//5
header_writer.write_u64::<LittleEndian>(granule_pos)?; // granule position //6-13
header_writer.write_u32::<LittleEndian>(self.serial)?; // Bitstream serial number//14-17
header_writer.write_u32::<LittleEndian>(page_index)?; // Page sequence number//18-21
header_writer.write_u32::<LittleEndian>(0)?; //Checksum reserve //22-25
header_writer.write_u8(n_segments as u8)?; // Number of segments in page //26
// Filling the segment table with the lacing values.
// First (n_segments - 1) values will always be 255.
for _ in 0..n_segments - 1 {
header_writer.write_u8(255)?;
}
// The last value will be the remainder.
header_writer.write_u8((self.last_payload_size - (n_segments * 255 - 255)) as u8)?;
header_writer.write_all(payload)?; // inserting at 28th since Segment Table(1) + header length(27)
}
let mut checksum = 0u32;
for v in &page {
checksum =
(checksum << 8) ^ self.checksum_table[(((checksum >> 24) as u8) ^ (*v)) as usize];
}
page[22..26].copy_from_slice(&checksum.to_le_bytes()); // Checksum - generating for page data and inserting at 22th position into 32 bits
self.writer.write_all(&page)?;
Ok(())
}
}
impl<W: Write> Writer for OggWriter<W> {
/// write_rtp adds a new packet and writes the appropriate headers for it
fn write_rtp(&mut self, packet: &rtp::Packet) -> Result<()> {
if packet.payload.is_empty() {
return Ok(());
}
let mut opus_packet = rtp::codec::opus::OpusPacket;
let payload = opus_packet.depacketize(&packet.payload)?;
// Should be equivalent to sample_rate * duration
if self.previous_timestamp != 1 {
let increment = packet.header.timestamp - self.previous_timestamp;
self.previous_granule_position += increment as u64;
}
self.previous_timestamp = packet.header.timestamp;
self.write_page(
&payload,
PAGE_HEADER_TYPE_CONTINUATION_OF_STREAM,
self.previous_granule_position,
self.page_index,
)?;
self.page_index += 1;
Ok(())
}
/// close stops the recording
fn close(&mut self) -> Result<()> {
let payload = self.last_payload.clone();
self.write_page(
&payload,
PAGE_HEADER_TYPE_END_OF_STREAM,
self.previous_granule_position,
self.page_index - 1,
)?;
self.writer.flush()?;
Ok(())
}
}