diff --git a/spx-gui/src/models/animation.test.ts b/spx-gui/src/models/animation.test.ts
index 91f09112e..e107a080e 100644
--- a/spx-gui/src/models/animation.test.ts
+++ b/spx-gui/src/models/animation.test.ts
@@ -81,7 +81,7 @@ describe('Animation', () => {
     expect(animation.sound).toBeNull()
   })
 
-  it('should load correctly', async () => {
+  it('should work correctly while project loads', async () => {
     const project = makeProject()
     project.sprites[0].animations[0].setSound(project.sounds[0].name)
 
diff --git a/spx-gui/src/models/animation.ts b/spx-gui/src/models/animation.ts
index df006ad20..0eb2b0e1f 100644
--- a/spx-gui/src/models/animation.ts
+++ b/spx-gui/src/models/animation.ts
@@ -10,13 +10,6 @@ import type { Files } from './common/file'
 import type { Costume, RawCostumeConfig } from './costume'
 import type { Sprite } from './sprite'
 
-enum AniType {
-  frame = 0,
-  move = 1,
-  turn = 2,
-  glide = 3
-}
-
 type ActionConfig = {
   /** Sound name to play */
   play?: string
@@ -27,19 +20,26 @@ type ActionConfig = {
 export const defaultFps = 10
 
 export type AnimationInits = {
+  /** Duration for animation to be played once */
   duration?: number
   onStart?: ActionConfig
 
   // not supported by builder:
-  fps?: number
   isLoop?: boolean // TODO
   onPlay?: ActionConfig
 }
 
-export type RawAnimationConfig = AnimationInits & {
+export type RawAnimationConfig = Omit<AnimationInits, 'duration'> & {
   anitype?: number
+  frameFrom?: number | string
+  frameTo?: number | string
+  frameFps?: number
+
+  // legacy APIs, for compatibility only:
   from?: number | string
   to?: number | string
+  fps?: number
+  duration?: number
 }
 
 export class Animation extends Disposable {
@@ -103,7 +103,7 @@ export class Animation extends Disposable {
     this.duration = inits?.duration ?? 0
     this.sound = inits?.onStart?.play ?? null
 
-    for (const field of ['fps', 'isLoop', 'onPlay'] as const) {
+    for (const field of ['isLoop', 'onPlay'] as const) {
       if (inits?.[field] != null) console.warn(`unsupported field: ${field} for sprite ${name}`)
     }
 
@@ -120,12 +120,31 @@ export class Animation extends Disposable {
     return animation
   }
 
-  static load(name: string, { from, to, ...inits }: RawAnimationConfig, sprite: Sprite) {
-    if (from == null || to == null) throw new Error(`from and to expected for Animation ${name}`)
-    const fromIndex = getCostumeIndex(sprite.costumes, from)
-    const toIndex = getCostumeIndex(sprite.costumes, to)
+  static load(
+    name: string,
+    {
+      frameFrom,
+      frameTo,
+      frameFps,
+      from,
+      to,
+      fps,
+      // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      duration: _spxDuration, // drop spx `duration`, which is different from ours
+      ...inits
+    }: RawAnimationConfig,
+    sprite: Sprite
+  ) {
+    frameFrom = frameFrom ?? from
+    frameTo = frameTo ?? to
+    frameFps = frameFps ?? fps
+    if (frameFrom == null || frameTo == null)
+      throw new Error(`from and to expected for Animation ${name}`)
+    const fromIndex = getCostumeIndex(sprite.costumes, frameFrom)
+    const toIndex = getCostumeIndex(sprite.costumes, frameTo)
     const costumes = sprite.costumes.slice(fromIndex, toIndex + 1)
-    const animation = new Animation(name, inits)
+    const duration = costumes.length / (frameFps ?? defaultFps)
+    const animation = new Animation(name, { ...inits, duration })
     animation.setCostumes(costumes.map((costume) => costume.clone()))
     for (const costume of costumes) {
       sprite.removeCostume(costume.name)
@@ -145,10 +164,9 @@ export class Animation extends Disposable {
       Object.assign(files, costumeFiles)
     }
     const config: RawAnimationConfig = {
-      from: costumeConfigs[0]?.name,
-      to: costumeConfigs[costumeConfigs.length - 1]?.name,
-      duration: this.duration,
-      anitype: AniType.frame,
+      frameFrom: costumeConfigs[0]?.name,
+      frameTo: costumeConfigs[costumeConfigs.length - 1]?.name,
+      frameFps: Math.ceil(this.costumes.length / this.duration),
       onStart: this.sound == null ? undefined : { play: this.sound }
     }
     return [config, costumeConfigs, files]
diff --git a/tools/ispx/go.mod b/tools/ispx/go.mod
index 3b00544cf..f7a933565 100644
--- a/tools/ispx/go.mod
+++ b/tools/ispx/go.mod
@@ -45,6 +45,7 @@ require (
 )
 
 replace (
+	github.com/goplus/spx => github.com/JiepengTan/spx v0.0.0-20240719133620-feffaabdead7
 	github.com/hajimehoshi/oto => github.com/hajimehoshi/oto v1.0.1
 	github.com/srwiley/oksvg => github.com/qiniu/oksvg v0.2.0-no-charset
 	golang.org/x/image => golang.org/x/image v0.0.0-20210628002857-a66eb6448b8d
diff --git a/tools/ispx/go.sum b/tools/ispx/go.sum
index 5bf088881..57a96472c 100644
--- a/tools/ispx/go.sum
+++ b/tools/ispx/go.sum
@@ -1,5 +1,7 @@
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/JiepengTan/spx v0.0.0-20240719133620-feffaabdead7 h1:1ao1rWUNLiVADvDobtydL1BoYwComcePTbTKBZV3kTg=
+github.com/JiepengTan/spx v0.0.0-20240719133620-feffaabdead7/go.mod h1:mFopcoTwo/IhdWUhQD1SmQfNdJyY7NPKnCcy5O1W9pc=
 github.com/ajstarks/deck v0.0.0-20200831202436-30c9fc6549a9/go.mod h1:JynElWSGnm/4RlzPXRlREEwqTHAN3T56Bv2ITsFT3gY=
 github.com/ajstarks/deck/generate v0.0.0-20210309230005-c3f852c02e19/go.mod h1:T13YZdzov6OU0A1+RfKZiZN9ca6VeKdBdyDV+BY97Tk=
 github.com/ajstarks/svgo v0.0.0-20210927141636-6d70534b1098 h1:iiPTCsr/y6MEke5leED5Bi/0zlznD44tlHQvTgLOJcE=
@@ -38,16 +40,6 @@ github.com/goplus/mod v0.13.9 h1:B9zZoHi2AzMltTSOFqZNVjqGlSMlhhNTWwEzVqhTQzg=
 github.com/goplus/mod v0.13.9/go.mod h1:MibsLSftGmxaQq78YzUzNviyFwB9RtpMaoscufvEKH4=
 github.com/goplus/reflectx v1.2.2 h1:T1p20OIH/HcnAvQQNnDLwl6AZOjU34icsfc6migD6L8=
 github.com/goplus/reflectx v1.2.2/go.mod h1:wHOS9ilbB4zrecI0W1dMmkW9JMcpXV7VjALVbNU9xfM=
-github.com/goplus/spx v1.0.1-0.20240625013919-ea894f504455 h1:/E/joCS3nu+VbxBsRt1j3OqQtACqO1nbMAf4yOVD0o0=
-github.com/goplus/spx v1.0.1-0.20240625013919-ea894f504455/go.mod h1:eP0Yfbt31hSgnVmfmVeSRnq/kRoDyhwz+mI3VeXb/Vo=
-github.com/goplus/spx v1.0.1-0.20240703050621-72b5b4f2242e h1:nlVcudZPaahpF7mn/HgHgIcNdqmbQP/ky5gF5UlLkWs=
-github.com/goplus/spx v1.0.1-0.20240703050621-72b5b4f2242e/go.mod h1:8HjcFxmoksU4fxQF0Kc4hBuRLpW2FkEJHmLuyMhY5w8=
-github.com/goplus/spx v1.0.1-0.20240708105507-8f9159acc876 h1:sV6oNNakUbjgCMC4PFjj/TvCbTGxCGaJIdUfFU3d4mw=
-github.com/goplus/spx v1.0.1-0.20240708105507-8f9159acc876/go.mod h1:mFopcoTwo/IhdWUhQD1SmQfNdJyY7NPKnCcy5O1W9pc=
-github.com/hajimehoshi/ebiten/v2 v2.7.5 h1:jN6FnhCd9NGYCsm5GtrweuikrlyVGCSUpH5YgL+7UKA=
-github.com/hajimehoshi/ebiten/v2 v2.7.5/go.mod h1:H2pHVgq29rfm5yeQ7jzWOM3VHsjo7/AyucODNLOhsVY=
-github.com/hajimehoshi/ebiten/v2 v2.7.6 h1:dKM/BdPZP+I/I0ElcqfQ1d06W+kA0nwhUOWzEdEBIbY=
-github.com/hajimehoshi/ebiten/v2 v2.7.6/go.mod h1:Ulbq5xDmdx47P24EJ+Mb31Zps7vQq+guieG9mghQUaA=
 github.com/hajimehoshi/ebiten/v2 v2.7.7 h1:FyiuIOZqKU4aefYVws/lBDhTZu2WY2m/eWI3PtXZaHs=
 github.com/hajimehoshi/ebiten/v2 v2.7.7/go.mod h1:Ulbq5xDmdx47P24EJ+Mb31Zps7vQq+guieG9mghQUaA=
 github.com/hajimehoshi/go-mp3 v0.3.2/go.mod h1:qMJj/CSDxx6CGHiZeCgbiq2DSUkbK0UbtXShQcnfyMM=
@@ -163,8 +155,6 @@ golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
 golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/text v0.14.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
-golang.org/x/text v0.15.0 h1:h1V/4gjBv8v9cjcR6+AR5+/cIYK5N/WAgiv4xlsEtAk=
-golang.org/x/text v0.15.0/go.mod h1:18ZOQIKpY8NJVqYksKHtTdi31H5itFRjB5/qKTNYzSU=
 golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=
 golang.org/x/text v0.16.0/go.mod h1:GhwF1Be+LQoKShO3cGOHzqOgRrGaYc9AvblQOmPVHnI=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
@@ -175,8 +165,6 @@ golang.org/x/tools v0.1.2/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
 golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
 golang.org/x/tools v0.19.0/go.mod h1:qoJWxmGSIBmAeriMx19ogtrEPrGtDbPK634QFIcLAhc=
-golang.org/x/tools v0.21.0 h1:qc0xYgIbsSDt9EyWz05J5wfa7LOVW0YTLOXrqdLAWIw=
-golang.org/x/tools v0.21.0/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d h1:vU5i/LfpvrRCpgM/VPfJLg5KjxD3E+hfT1SH+d9zLwg=
 golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxbQROHiO6hDPo2LHcIPhhQsa9DLh0yGk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=