You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/webrtc/rtp/src/codecs/vp8
    
    the code of the file until where you have to start completion: #[cfg(test)]
mod vp8_test;

use bytes::{Buf, BufMut, Bytes, BytesMut};

use crate::error::{Error, Result};
use crate::packetizer::{Depacketizer, Payloader};

pub const VP8_HEADER_SIZE: usize = 1;

/// Vp8Payloader payloads VP8 packets
#[derive(Default, Debug, Copy, Clone)]
pub struct Vp8Payloader {
    pub enable_picture_id: bool,
    picture_id: u16,
}

impl Payloader for Vp8Payloader {
    /// Payload fragments a VP8 packet across one or more byte arrays
    fn payload(&mut self, mtu: usize, payload: &Bytes) -> Result<Vec<Bytes>> {
        if payload.is_empty() || mtu == 0 {
            return Ok(vec![]);
        }

        /*
         * https://tools.ietf.org/html/rfc7741#section-4.2
         *
         *       0 1 2 3 4 5 6 7
         *      +-+-+-+-+-+-+-+-+
         *      |X|R|N|S|R| PID | (REQUIRED)
         *      +-+-+-+-+-+-+-+-+
         * X:   |I|L|T|K| RSV   | (OPTIONAL)
         *      +-+-+-+-+-+-+-+-+
         * I:   |M| PictureID   | (OPTIONAL)
         *      +-+-+-+-+-+-+-+-+
         * L:   |   tl0picidx   | (OPTIONAL)
         *      +-+-+-+-+-+-+-+-+
         * T/K: |tid|Y| KEYIDX  | (OPTIONAL)
         *      +-+-+-+-+-+-+-+-+
         *  S: Start of VP8 partition.  SHOULD be set to 1 when the first payload
         *     octet of the RTP packet is the beginning of a new VP8 partition,
         *     and MUST NOT be 1 otherwise.  The S bit MUST be set to 1 for the
         *     first packet of each encoded frame.
         */
        let using_header_size = if self.enable_picture_id {
            if self.picture_id == 0 || self.picture_id < 128 {
                VP8_HEADER_SIZE + 2
            } else {
 
    
    fn depacketize(&mut self, packet: &Bytes) -> Result<Bytes> {
        let payload_len = packet.len();
        if payload_len < 4 {
            return Err(Error::ErrShortPacket);
        }
        //    0 1 2 3 4 5 6 7                      0 1 2 3 4 5 6 7
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        //    |X|R|N|S|R| PID | (REQUIRED)        |X|R|N|S|R| PID | (REQUIRED)
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        // X: |I|L|T|K| RSV   | (OPTIONAL)   X:   |I|L|T|K| RSV   | (OPTIONAL)
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        // I: |M| PictureID   | (OPTIONAL)   I:   |M| PictureID   | (OPTIONAL)
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        // L: |   tl0picidx   | (OPTIONAL)        |   PictureID   |
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        //T/K:|tid|Y| KEYIDX  | (OPTIONAL)   L:   |   tl0picidx   | (OPTIONAL)
        //    +-+-+-+-+-+-+-+-+                   +-+-+-+-+-+-+-+-+
        //T/K:|tid|Y| KEYIDX  | (OPTIONAL)
        //    +-+-+-+-+-+-+-+-+

        let reader = &mut packet.clone();
        let mut payload_index = 0;

        let mut b = reader.get_u8();
        payload_index += 1;

        self.x = (b & 0x80) >> 7;
        self.n = (b & 0x20) >> 5;
        self.s = (b & 0x10) >> 4;
        self.pid = b & 0x07;

        if self.x == 1 {
            b = reader.get_u8();
            payload_index += 1;
            self.i = (b & 0x80) >> 7;
            self.l = (b & 0x40) >> 6;
            self.t = (b & 0x20) >> 5;
            self.k = (b & 0x10) >> 4;
        }

        if self.i == 1 {
            b = reader.get_u8();
            payload_index += 1;
            // PID present?
            if b & 0x80 > 0 {
                // M == 1, PID is 16bit
                self.picture_id = (((b & 0x7f) as u16) << 8) | (reader.get_u8() as u16);
                payload_index += 1;
            } else {
                self.picture_id = b as u16;
            }
        }

        if payload_index >= payload_len {
            return Err(Error::ErrShortPacket);
        }

        if self.l == 1 {
            self.tl0_pic_idx = reader.get_u8();
            payload_index += 1;
        }

        if payload_index >= payload_len {
            return Err(Error::ErrShortPacket);
        }

        if self.t == 1 || self.k == 1 {
            let b = reader.get_u8();
            if self.t == 1 {
                self.tid = b >> 6;
                self.y = (b >> 5) & 0x1;
            }
            if self.k == 1 {
                self.key_idx = b & 0x1F;
            }
            payload_index += 1;
        }

        if payload_index >= packet.len() {
            return Err(Error::ErrShortPacket);
        }

        Ok(packet.slice(payload_index..))
    }