Implementation for SWS scale (#33)

* Draft implementation for SWS scale

* Update go.mod

* Revert "Update go.mod"

This reverts commit 760fb8c427.

* Renaming to AllocSwsContext and remove ChangeResolution this should handled by users

* update example to use new name and remove ChangeResolution

* Follow scaling example from libav, update readme, improve sws

Change scaling example to an similar libav example
Update readme
Add func to UpdateScalingParameters
Rename AllocSwsContext to SwsGetContext
Using a type for scaling algos/flags

* Fix Errors in scale example

* Review Changes

Now using sws context flags
Restructer sws context and adding ned simpler methods to update the ctx
Update the example
Update the test

* Correctly handle error for buffer alloc in PrepareDestinationFrameForScaling

* Add more getter and setter for sws

Get/Set source w,h,pixfmt
Get/Set dst w,h,pixfmt
Get/Set sws flags

* Adding resolution get/set

* Use CachedContext when updating sws ctx

* Review changes

Reorder flags, and update them
# Update Example
Use renaming function to create sws context
Clean up
Use new framdata image funcs
# Sws scale context
New way to update the context
Use sws_scale_frame instead of sws_scale
Reordering funcs for get and set
# Sws sclate context flag
Add "Flag" for algo name
# Update sws test

* fix fmt error args bug

* Review Changes

Simpfy sws update
Use c.int for sws flags
update test

examples/scaling/main.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"image/png"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/asticode/go-astiav"
+)
+
+var (
+	output    = flag.String("o", "", "the png output path")
+	dstWidth  = flag.Int("w", 50, "destination width")
+	dstHeight = flag.Int("h", 50, "destination height")
+)
+
+func main() {
+	// Handle ffmpeg logs
+	astiav.SetLogLevel(astiav.LogLevelDebug)
+	astiav.SetLogCallback(func(l astiav.LogLevel, fmt, msg, parent string) {
+		log.Printf("ffmpeg log: %s (level: %d)\n", strings.TrimSpace(msg), l)
+	})
+
+	// Parse flags
+	flag.Parse()
+
+	// Usage
+	if *output == "" || *dstWidth <= 0 || *dstHeight <= 0 {
+		log.Println("Usage: <binary path> -o <output path> -w <output width> -h <output height>")
+		return
+	}
+
+	// Create destination file
+	dstFile, err := os.Create(*output)
+	if err != nil {
+		log.Fatal(fmt.Errorf("main: creating %s failed: %w", *output, err))
+	}
+	defer dstFile.Close()
+
+	// Create source frame
+	srcFrame := astiav.AllocFrame()
+	defer srcFrame.Free()
+	srcFrame.SetWidth(320)
+	srcFrame.SetHeight(240)
+	srcFrame.SetPixelFormat(astiav.PixelFormatYuv420P)
+	if err = srcFrame.AllocBuffer(1); err != nil {
+		log.Fatal(fmt.Errorf("main: allocating source frame buffer failed: %w", err))
+	}
+	if err = srcFrame.ImageFillBlack(); err != nil {
+		log.Fatal(fmt.Errorf("main: filling source frame with black image failed: %w", err))
+	}
+
+	// Create destination frame
+	dstFrame := astiav.AllocFrame()
+	defer dstFrame.Free()
+
+	// Create software scale context
+	swsCtx, err := astiav.CreateSoftwareScaleContext(
+		srcFrame.Width(),
+		srcFrame.Height(),
+		srcFrame.PixelFormat(),
+		*dstWidth,
+		*dstHeight,
+		astiav.PixelFormatRgba,
+		astiav.NewSoftwareScaleContextFlags(astiav.SoftwareScaleContextFlagBilinear),
+	)
+	if err != nil {
+		log.Fatal(fmt.Errorf("main: creating software scale context failed: %w", err))
+	}
+	defer swsCtx.Free()
+
+	// Scale frame
+	if err := swsCtx.ScaleFrame(srcFrame, dstFrame); err != nil {
+		log.Fatal(fmt.Errorf("main: scaling frame failed: %w", err))
+	}
+
+	// Guess destination image format
+	img, err := dstFrame.Data().GuessImageFormat()
+	if err != nil {
+		log.Fatal(fmt.Errorf("main: guessing destination image format failed: %w", err))
+	}
+
+	// Copy frame data to destination image
+	if err = dstFrame.Data().ToImage(img); err != nil {
+		log.Fatal(fmt.Errorf("main: copying frame data to destination image failed: %w", err))
+	}
+
+	// Encode to png
+	if err = png.Encode(dstFile, img); err != nil {
+		log.Fatal(fmt.Errorf("main: encoding to png failed: %w", err))
+	}
+
+	// Success
+	log.Println("success")
+}