Trait ImageDecoder 

pub trait ImageDecoder {
    type Adapter: ImageAdapter;
    type Buffer: AsRef<[u8]>;
    type Error;

    // Required method
    fn decode(
        &mut self,
        packet: &AttachmentPacket<<Self::Adapter as ImageAdapter>::PacketExtra, Self::Buffer>,
    ) -> Result<ImageFrame<<Self::Adapter as ImageAdapter>::PixelFormat, <Self::Adapter as ImageAdapter>::FrameExtra, Self::Buffer>, Self::Error>;
}

One-shot still-image decoder — cover art, an embedded thumbnail, a poster frame.

No Stream in the name, and no rhythm to go with it. An attachment track delivers exactly one packet (see Demuxer’s attachment contract), that packet is a whole file, and decoding it produces exactly one picture. There is nothing to queue, nothing to drain, and no end-of-stream to signal — so decode takes the packet and returns the frame, instead of the send_packet / receive_frame split the two *StreamDecoder traits need. SubtitleDecoder keeps that split only because FFmpeg’s own subtitle API is push-shaped; nothing forces it here.

The frame has no timestamps, because ImageFrame has no seats for them.

Where the input comes from

A container’s still images arrive as TrackKind::Attachment tracks: the track row says what codec the picture is in, and the track’s one AttachmentPacket carries its bytes. So the row opens the decoder — off-trait, per the module docs — and the packet is what decode is handed.

&mut self

Decoding one image needs no state across calls; the exclusive borrow is here because a backend’s decoder handle is a mutable resource (FFmpeg’s AVCodecContext is), and because it lets a backend reuse one open decoder across several attachments of the same codec rather than reopening per picture.

Required Associated Types

type Adapter: ImageAdapter

Backend-specific vocabulary.

type Buffer: AsRef<[u8]>

Buffer type held by the packet this decoder accepts and the frame it produces. See the module docs for what may be bound here.

type Error

Decoder-specific error type.

Required Methods

fn decode( &mut self, packet: &AttachmentPacket<<Self::Adapter as ImageAdapter>::PacketExtra, Self::Buffer>, ) -> Result<ImageFrame<<Self::Adapter as ImageAdapter>::PixelFormat, <Self::Adapter as ImageAdapter>::FrameExtra, Self::Buffer>, Self::Error>

Decodes one attachment payload — a whole image file — into a still.

Backends signal “these bytes are not a picture this decoder can read” through a backend-specific Error variant, never by returning an empty frame. That is not the receive-path convention wearing different clothes: Received names the states of a session — nothing yet, over — and a one-shot decode has neither. “These bytes are not a picture” is a fact about the payload the caller handed over, which is what an error is for.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors