file metadata

An ansi.moe file should start with:

• a little-endian 8 byte integer, describing the length in bytes of the serialized metadata
• a messagepack-encoded blob: the metadata!

the metadata is a structure defined as such:

struct VideoMetadata {
    pub video_tracks: Vec<VideoTrack>, // list of video tracks in the file
    pub subtitle_tracks: Vec<SubtitleTrack>, // list of subtitle tracks in the file
    pub attachments: Vec<Attachment>, // list of attachments to the file
    pub compression: CompressionMode, // compression mode of this file: 0 = None; 1 = Zstd-compressed
}

where VideoTrack is:

 struct VideoTrack {
    pub name: Option<String>, // optional name for the track
    pub color_mode: ColorMode, // what color mode does the track use: 0 = True; 1 = 8bit
    pub height: u32,           // height in pixels (divide by two to get line count for terminal)
    pub width: u32,            // width in pixels
    pub codec_private: Option<Vec<u8>>, // data you may need to use to decode this track's packet data (currently unused)
    pub index: u16 // index the packets of this track will have
}

SubtitleTrack is:

struct SubtitleTrack {
    pub name: Option<String>, // optional name for the track
    pub lang: Option<String>, // optional language for the track
    pub format: SubtitleFormat, // format for the subtitles (currently an enum: SubRip | SubStationAlpha | Unknown(String))
    pub codec_private: Option<Vec<u8>>, // data you may need to use to decode this track's packet data (used in SSA tracks to store the SSA header!)
    pub index: u16, // index the packets of this track will have
}

and Attachment is:

enum Attachment {
    Binary(Vec<u8>),
    Midi(Vec<u8>),
}

what follows is the video's packets..

packets

Decoded packet

A decoded ansi.moe packet - the ones you want to get from your demuxer - should probably look something like this:

• the index of the stream it belongs to
• the time the packet's contents should be shown by the player
• how long it should be shown for
• a key-value map of extra parameters for this codec: both keys and values are stored as 4byte unsigned integers.
• the binary data of the packet

In Rust, it could look like this:

struct Packet {
    stream_index: u16,
    presentation_length: Duration,
    presentation_time: Duration,
    data: Vec<u8>,
    extra_data: BTReeMap<u32, u32>,
}

Encoded packet

The encoded - or wire - form of an ansi.moe packet is a bit more strictly defined. This is what you'll find stored in .ansi files or network streams, and need to transform to the decoded packets.

It's composed of a header - defined as a C-ABI struct - and a binary blob.

note: all fields are little endian unsigned integers!

The binary blob is composed of:

• a byte string extra_data_length bytes long; interpreted as a list of (key: u32, value: u32) pairs
• a byte string data_length bytes long; the packet's data itself.

Extra Data flags

Here's some flags you may find in the extra_data map: