Module Swscale

The version of the libswscale loaded at run time, read once when the module is loaded.

A flag of a scaler; the flags of a list are combined. Fast_bilinear, Bilinear and Bicubic select the scaling algorithm. Print_info makes libswscale log its scaling parameters, through FFmpeg's logging.

A scaler bound to an input size and pixel format and an output size and pixel format. It scales on one thread and works on caller-supplied bigarrays, in place, with scale. It owns its native scaler, released when the value is collected.

create flags in_width in_height in_format out_width out_height out_format creates a scaler. The arguments are, in order: the flags, the input width and height in pixels, the input pixel format, the output width and height in pixels and the output pixel format. Every other setting keeps FFmpeg's default.

The call releases the OCaml runtime lock while the scaler is initialised.

• raises Avutil.Error

  with `Failure _ when a width or a height is below 1; with the FFmpeg error when FFmpeg rejects a setting or fails to initialise the scaler.

The buffers of an image: one (plane, line_size) pair per plane of the pixel format, in plane order. line_size is in bytes. A paletted format has its palette as one more buffer after the plane.

scale scaler src y h dst off scales a slice of the input image: the h rows that start at row y. src holds the planes of that slice and dst the planes the output is written to.

off is a number of rows: the output image starts at row off of the dst planes. For a plane with vertical chroma subsampling the row count is reduced accordingly.

libswscale reads src and writes dst in place; nothing is copied. The call releases the OCaml runtime lock and excludes every other operation on the scaler: a concurrent one raises Error (`Failure "Object in use!") at once. After a failure the scaler stays usable.

• raises Avutil.Error

  with `Failure _, before anything is read or written, when src or dst holds fewer buffers than its pixel format needs, when y, h or off is negative, when the slice lies outside the input height, when off is not a multiple of the vertical chroma subsampling factor, when a line size is smaller than the format needs for the image width and when a plane is shorter than the rows read from or written to it; with the FFmpeg error when scaling fails.

How a value of type 'a holds an image. Only the four data modules at the end of this interface provide values of this type.

A data type a scaler reads or writes: one of BigArray, PackedBigArray, Frame and Bytes. A program passes two of them to Make.

A scaler from images of type 'i to images of type 'o. It owns its native scaler, released when the value is collected, and keeps nothing of the values given to it or returned by it.

Scalers that read images of type I.t and return images of type O.t.

One (plane, line_size) pair per plane, the planes in bigarrays.

The planes in one array and their line sizes, in bytes, in a second array of the same length.

Video frames.

One (plane, line_size) pair per plane, the planes in strings. Each conversion copies them.