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frame.go
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frame.go
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package prores
import (
"encoding/binary"
"fmt"
"image"
"io"
)
type FrameFlags byte
func (f FrameFlags) SubsampleRatio() image.YCbCrSubsampleRatio {
if (f & 0xc0) == 0xc0 {
return image.YCbCrSubsampleRatio444
}
return image.YCbCrSubsampleRatio422
}
type InterlaceMode int
const (
InterlaceModeNone InterlaceMode = 0
InterlaceModeTopFirst InterlaceMode = 1
InterlaceModeTopSecond InterlaceMode = 2
)
func (f FrameFlags) InterlaceMode() InterlaceMode {
return InterlaceMode((f & 0x0c) >> 2)
}
type FrameAlphaInfo byte
func (i FrameAlphaInfo) HasAlpha() bool {
return i != 0
}
type FrameQuantizationMatrixFlags byte
func (f FrameQuantizationMatrixFlags) CustomLumaQuantizationMatrixPresent() bool {
return (f & 2) != 0
}
func (f FrameQuantizationMatrixFlags) CustomChromaQuantizationMatrixPresent() bool {
return (f & 1) != 0
}
var defaultQuantizationMatrix = []int8{
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4,
}
type FrameHeader struct {
HeaderSize int64
Version int
Width int
Height int
Flags FrameFlags
AlphaInfo FrameAlphaInfo
QuantizationMatrixFlags FrameQuantizationMatrixFlags
CustomLumaQuantizationMatrix []int8
CustomChromaQuantizationMatrix []int8
}
func (h *FrameHeader) LumaQuantizationMatrix() []int8 {
if h.CustomLumaQuantizationMatrix != nil {
return h.CustomLumaQuantizationMatrix
}
return defaultQuantizationMatrix
}
func (h *FrameHeader) ChromaQuantizationMatrix() []int8 {
if h.CustomChromaQuantizationMatrix != nil {
return h.CustomChromaQuantizationMatrix
}
return h.LumaQuantizationMatrix()
}
func (h *FrameHeader) Decode(r io.ReaderAt) error {
var hdrSizeBuf [2]byte
if _, err := r.ReadAt(hdrSizeBuf[:], 0); err != nil {
return err
}
hdrSize := binary.BigEndian.Uint16(hdrSizeBuf[:])
if hdrSize < 28 {
return fmt.Errorf("header size must be at least 28")
} else if hdrSize > 1024 {
// to keep us from choking on bad data. not dictated by spec
return fmt.Errorf("header size must be less than or equal to 1024")
}
buf := make([]byte, hdrSize)
if _, err := r.ReadAt(buf, 0); err != nil {
return err
}
decoded := FrameHeader{
HeaderSize: int64(hdrSize),
Version: int(binary.BigEndian.Uint16(buf[2:])),
Width: int(binary.BigEndian.Uint16(buf[8:])),
Height: int(binary.BigEndian.Uint16(buf[10:])),
Flags: FrameFlags(buf[12]),
AlphaInfo: FrameAlphaInfo(buf[17] & 0x0f),
QuantizationMatrixFlags: FrameQuantizationMatrixFlags(buf[19]),
}
customMatrixOffset := 20
if decoded.QuantizationMatrixFlags.CustomLumaQuantizationMatrixPresent() {
m := make([]int8, 64)
for i := range m {
m[i] = int8(buf[customMatrixOffset+i])
}
decoded.CustomLumaQuantizationMatrix = m
customMatrixOffset += 64
}
if decoded.QuantizationMatrixFlags.CustomChromaQuantizationMatrixPresent() {
m := make([]int8, 64)
for i := range m {
m[i] = int8(buf[customMatrixOffset+i])
}
decoded.CustomChromaQuantizationMatrix = m
}
*h = decoded
return nil
}
func DecodeFrame(r io.ReaderAt, size int64) (image.Image, error) {
var header FrameHeader
if err := header.Decode(r); err != nil {
return nil, err
}
return DecodePicture(io.NewSectionReader(r, header.HeaderSize, size-header.HeaderSize), &header, FieldOrderFirst)
}