Struct PreviewOptions 

pub struct PreviewOptions {
    pub frames_per_second: u64,
    pub scale: u32,
    pub previews_per_second: u64,
    pub budget_bytes: u64,
}

How the index trades memory and pass length against how fine the scrub is.

Every field has a defensible default and a reason a caller would change it, which is why this is a struct rather than three arguments: a 4K source wants a smaller scale than a 480p one, a long documentary wants fewer previews per second than a short clip, and an embedded caller wants a smaller budget_bytes than a desktop editor.

Fields

frames_per_second: u64

The source’s frame rate, which is what turns previews_per_second into a frame stride.

scale: u32

How far each preview is shrunk on each axis.

A preview is drawn stretched back over the whole video quad, so this is a resolution the picture is recognizable at rather than one it is sharp at: a quarter on each axis is a sixteenth of the memory and reads as the right shot on a 1080p source. The exact frame replaces it shortly anyway.

previews_per_second: u64

How many previews a second of playback gets, when memory allows it.

Closer together is a finer scrub but a longer pass - every preview is a full-resolution picture the reader has to convert before it can be shrunk, and until the pass reaches the far end of the track a lookup there falls back to an earlier picture. Half a second apart is about as coarse as a scrub can be before the picture stops answering “which shot is this”.

budget_bytes: u64

A ceiling on what the whole index may hold.

The stride follows from this and the track length rather than being fixed, so a long track keeps fewer, further-apart previews instead of growing without bound. At a quarter scale a 1080p preview is 480x270x4 bytes, so the default holds about 129 of them.

Implementations

impl PreviewOptions

pub fn for_frame_rate(frames_per_second: u64) -> Self

The defaults, for a source running at frames_per_second.

pub fn stride(&self, dimensions: &VideoDimensions, frame_count: u64) -> u64

How many frames apart the previews are: previews_per_second of playback, or further apart when that many would not fit in the budget.

pub fn preview_bytes(&self, dimensions: &VideoDimensions) -> u64

What one preview of a dimensions source costs in memory.

Trait Implementations

impl Clone for PreviewOptions

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for PreviewOptions

impl Debug for PreviewOptions

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for PreviewOptions

impl PartialEq for PreviewOptions

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for PreviewOptions