fix: start animated AVIF motion at sentence start, not audio padding

- Removed leading padding from AVIF clip start so pre-sentence frames are not shown
- Duration now extends by trailing padding only
- Added regression test verifying -ss and -t args against a stub ffmpeg

changes/animated-avif-padding-freeze.md

@@ -0,0 +1,4 @@
+type: fixed
+area: anki
+
+- Kept animated AVIF card images from showing pre-sentence motion on multi-line mines without delaying motion after sentence audio starts.

src/media-generator.test.ts

@@ -1,7 +1,10 @@
 import assert from 'node:assert/strict';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
 import test from 'node:test';
 
-import { buildAnimatedImageVideoFilter } from './media-generator';
+import { buildAnimatedImageVideoFilter, MediaGenerator } from './media-generator';
 
 test('buildAnimatedImageVideoFilter prepends a cloned first frame when lead-in is provided', () => {
   assert.equal(
@@ -13,3 +16,55 @@ test('buildAnimatedImageVideoFilter prepends a cloned first frame when lead-in i
     'tpad=start_duration=1.25:start_mode=clone,fps=10,scale=w=640:h=-2',
   );
 });
+
+test('generateAnimatedImage starts motion with sentence audio instead of delaying for audio padding', async () => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'subminer-media-generator-test-'));
+  const binDir = path.join(root, 'bin');
+  const tempDir = path.join(root, 'media');
+  const argsPath = path.join(root, 'ffmpeg-args.txt');
+  fs.mkdirSync(binDir, { recursive: true });
+  const ffmpegPath = path.join(binDir, 'ffmpeg');
+  fs.writeFileSync(
+    ffmpegPath,
+    [
+      '#!/bin/sh',
+      'if [ "$1" = "-hide_banner" ] && [ "$2" = "-encoders" ]; then',
+      '  echo " V..... libaom-av1"',
+      '  exit 0',
+      'fi',
+      'printf "%s\\n" "$@" > "$SUBMINER_TEST_FFMPEG_ARGS"',
+      'out=""',
+      'for arg in "$@"; do out="$arg"; done',
+      'printf avif > "$out"',
+    ].join('\n'),
+    'utf8',
+  );
+  fs.chmodSync(ffmpegPath, 0o755);
+
+  const originalPath = process.env.PATH;
+  const originalArgsPath = process.env.SUBMINER_TEST_FFMPEG_ARGS;
+  process.env.PATH = `${binDir}${path.delimiter}${originalPath ?? ''}`;
+  process.env.SUBMINER_TEST_FFMPEG_ARGS = argsPath;
+  const generator = new MediaGenerator(tempDir);
+
+  try {
+    await generator.generateAnimatedImage('/video.mp4', 10, 12, 0.5, {
+      fps: 10,
+      maxWidth: 640,
+    });
+
+    const args = fs.readFileSync(argsPath, 'utf8').trim().split('\n');
+    assert.equal(args[args.indexOf('-ss') + 1], '10');
+    assert.equal(args[args.indexOf('-t') + 1], '2.5');
+    assert.equal(args[args.indexOf('-vf') + 1], 'fps=10,scale=w=640:h=-2');
+  } finally {
+    generator.cleanup();
+    process.env.PATH = originalPath;
+    if (originalArgsPath === undefined) {
+      delete process.env.SUBMINER_TEST_FFMPEG_ARGS;
+    } else {
+      process.env.SUBMINER_TEST_FFMPEG_ARGS = originalArgsPath;
+    }
+    fs.rmSync(root, { recursive: true, force: true });
+  }
+});

src/media-generator.ts

@@ -319,9 +319,11 @@ export class MediaGenerator {
       leadingStillDuration?: number;
     } = {},
   ): Promise<Buffer> {
-    const start = Math.max(0, startTime - padding);
-    const duration = endTime - startTime + 2 * padding;
     const { fps = 10, maxWidth = 640, maxHeight, crf = 35, leadingStillDuration = 0 } = options;
+    const safePadding = Number.isFinite(padding) ? Math.max(0, padding) : 0;
+    const start = Math.max(0, startTime);
+    const duration = endTime - startTime + safePadding;
+    const totalLeadingStillDuration = Math.max(0, leadingStillDuration);
 
     const clampedCrf = Math.max(0, Math.min(63, crf));
 
@@ -359,7 +361,7 @@ export class MediaGenerator {
             fps,
             maxWidth,
             maxHeight,
-            leadingStillDuration,
+            leadingStillDuration: totalLeadingStillDuration,
           }),
           ...encoderArgs,
           '-y',