scuffle_mp4/boxes/types/
ctts.rs

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use std::io;

use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
use bytes::Bytes;

use crate::boxes::header::{BoxHeader, FullBoxHeader};
use crate::boxes::traits::BoxType;

#[derive(Debug, Clone, PartialEq)]
/// Composition Time to Sample Box
/// ISO/IEC 14496-12:2022(E) - 8.6.1
pub struct Ctts {
    pub header: FullBoxHeader,
    pub entries: Vec<CttsEntry>,
}

#[derive(Debug, Clone, PartialEq)]
/// Entry in the Composition Time to Sample Box
pub struct CttsEntry {
    pub sample_count: u32,
    pub sample_offset: i64,
}

impl BoxType for Ctts {
    const NAME: [u8; 4] = *b"ctts";

    fn demux(header: BoxHeader, data: Bytes) -> io::Result<Self> {
        let mut reader = io::Cursor::new(data);

        let header = FullBoxHeader::demux(header, &mut reader)?;

        let entry_count = reader.read_u32::<BigEndian>()?;

        let mut entries = Vec::with_capacity(entry_count as usize);

        for _ in 0..entry_count {
            let sample_count = reader.read_u32::<BigEndian>()?;
            let sample_offset = if header.version == 1 {
                reader.read_i32::<BigEndian>()? as i64
            } else {
                reader.read_u32::<BigEndian>()? as i64
            };

            entries.push(CttsEntry {
                sample_count,
                sample_offset,
            });
        }

        Ok(Self { header, entries })
    }

    fn primitive_size(&self) -> u64 {
        self.header.size()
        + 4 // entry_count
        + (self.entries.len() as u64 * 8) // entries
    }

    fn primitive_mux<T: io::Write>(&self, writer: &mut T) -> io::Result<()> {
        self.header.mux(writer)?;

        writer.write_u32::<BigEndian>(self.entries.len() as u32)?;

        for entry in &self.entries {
            writer.write_u32::<BigEndian>(entry.sample_count)?;

            if self.header.version == 1 {
                writer.write_i32::<BigEndian>(entry.sample_offset as i32)?;
            } else {
                writer.write_u32::<BigEndian>(entry.sample_offset as u32)?;
            }
        }

        Ok(())
    }

    fn validate(&self) -> io::Result<()> {
        if self.header.flags != 0 {
            return Err(io::Error::new(io::ErrorKind::InvalidData, "ctts flags must be 0"));
        }

        if self.header.version > 1 {
            return Err(io::Error::new(io::ErrorKind::InvalidData, "ctts version must be 0 or 1"));
        }

        Ok(())
    }
}