vsd-mp4 0.2.0

MP4 parser ported from shaka-player with decryption and subtitle extraction support.
Documentation 
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use crate::{Mp4Parser, ParsedBox, Result, data, parser};

/// Track Encryption Box (tenc) - default encryption parameters for a track.
///
/// This box is found in the protection scheme info (sinf/schi) and provides
/// the default KID, IV size, and pattern encryption parameters.
#[derive(Debug, Clone)]
pub struct TencBox {
    /// The default Key ID for this track.
    pub default_kid: [u8; 16],
    /// Whether the track is protected (encrypted).
    pub is_protected: bool,
    /// Per-sample IV size (0 means constant IV is used, typically for CBCS).
    pub per_sample_iv_size: u8,
    /// Number of 16-byte blocks to encrypt in pattern mode (CENS/CBCS).
    /// Only present in tenc version 1.
    pub crypt_byte_block: u8,
    /// Number of 16-byte blocks to skip in pattern mode (CENS/CBCS).
    /// Only present in tenc version 1.
    pub skip_byte_block: u8,
    /// Constant IV for CBCS mode (when per_sample_iv_size is 0).
    pub constant_iv: Option<[u8; 16]>,
}

impl TencBox {
    /// Parse a tenc box from init segment data.
    ///
    /// This method navigates through the MP4 box hierarchy to find and parse
    /// the tenc box.
    pub fn from_init(data: &[u8]) -> Result<Option<Self>> {
        let tenc_box = data!();
        let tenc_box_c = tenc_box.clone();

        Mp4Parser::new()
            .base_box("moov", parser::children)
            .base_box("trak", parser::children)
            .base_box("mdia", parser::children)
            .base_box("minf", parser::children)
            .base_box("stbl", parser::children)
            .full_box("stsd", parser::sample_description)
            .base_box("encv", parser::visual_sample_entry)
            .base_box("enca", parser::audio_sample_entry)
            .base_box("sinf", parser::children)
            .base_box("schi", parser::children)
            .full_box("tenc", move |mut box_| {
                *tenc_box_c.borrow_mut() = Some(Self::new(&mut box_)?);
                Ok(())
            })
            .parse(data, true, false)?;

        Ok(tenc_box.take())
    }

    /// Parse a `tenc` box from a `ParsedBox`.
    pub fn new(box_: &mut ParsedBox) -> Result<Self> {
        let reader = &mut box_.reader;
        let version = box_.version.unwrap_or(0);

        // Skip first reserved byte
        reader.skip(1)?;

        // In version 0, skip another reserved byte
        // In version 1, read crypt/skip pattern blocks
        let (crypt_byte_block, skip_byte_block) = if version == 0 {
            reader.skip(1)?;
            (0, 0)
        } else {
            let pattern = reader.read_u8()?;
            ((pattern >> 4) & 0x0F, pattern & 0x0F)
        };

        let is_protected = reader.read_u8()? != 0;
        let per_sample_iv_size = reader.read_u8()?;

        let kid_bytes = reader.read_bytes_u8(16)?;
        let mut default_kid = [0u8; 16];
        default_kid.copy_from_slice(&kid_bytes);

        // Read constant IV if per_sample_iv_size is 0 (CBCS mode)
        let mut constant_iv = None;

        if per_sample_iv_size == 0 {
            let constant_iv_size = reader.read_u8()?;
            if constant_iv_size > 0 && constant_iv_size <= 16 {
                let bytes = reader.read_bytes_u8(constant_iv_size as usize)?;
                let mut iv = [0u8; 16];
                iv[..bytes.len()].copy_from_slice(&bytes);
                constant_iv = Some(iv);
            }
        }

        Ok(Self {
            default_kid,
            is_protected,
            per_sample_iv_size,
            crypt_byte_block,
            skip_byte_block,
            constant_iv,
        })
    }

    /// Get the default Key ID as a hexadecimal string.
    pub fn default_kid_hex(&self) -> String {
        hex::encode(self.default_kid)
    }
}