feat: refactor preview to support random fragment extraction

3 files changed, 89 insertions, 4 deletions

diff --git a/src/api/utils/ThumbUtil.js b/src/api/utils/ThumbUtil.js
index 5cfd9c0..2931d3b 100644
--- a/src/api/utils/ThumbUtil.js
+++ b/src/api/utils/ThumbUtil.js
@@ -2,7 +2,7 @@ const jetpack = require('fs-jetpack');
 const path = require('path');
 const sharp = require('sharp');
 const ffmpeg = require('fluent-ffmpeg');
-const previewUtil = require('./PreviewUtil');
+const previewUtil = require('./videoPreview/FragmentPreview');
 
 const log = require('./Log');
 
diff --git a/src/api/utils/videoPreview/FragmentPreview.js b/src/api/utils/videoPreview/FragmentPreview.js
new file mode 100644
index 0000000..8815392
--- /dev/null
+++ b/src/api/utils/videoPreview/FragmentPreview.js
@@ -0,0 +1,87 @@
+const ffmpeg = require('fluent-ffmpeg');
+const probe = require('ffmpeg-probe');
+
+const noop = () => {};
+
+const getRandomInt = (min, max) => {
+	const minInt = Math.ceil(min);
+	const maxInt = Math.floor(max);
+
+	// eslint-disable-next-line no-mixed-operators
+	return Math.floor(Math.random() * (maxInt - minInt + 1) + minInt);
+};
+
+const getStartTime = (vDuration, fDuration, ignoreBeforePercent, ignoreAfterPercent) => {
+	// by subtracting the fragment duration we can be sure that the resulting
+	// start time + fragment duration will be less than the video duration
+	const safeVDuration = vDuration - fDuration;
+
+	// if the fragment duration is longer than the video duration
+	if (safeVDuration <= 0) {
+		return 0;
+	}
+
+	return getRandomInt(ignoreBeforePercent * safeVDuration, ignoreAfterPercent * safeVDuration);
+};
+
+module.exports = async opts => {
+	const {
+		log = noop,
+
+		// general output options
+		quality = 2,
+		width,
+		height,
+		input,
+		output,
+
+		fragmentDurationSecond = 3,
+		ignoreBeforePercent = 0.25,
+		ignoreAfterPercent = 0.75
+	} = opts;
+
+	const info = await probe(input);
+
+	let { duration } = info.format;
+	duration = parseInt(duration, 10);
+
+	const startTime = getStartTime(duration, fragmentDurationSecond, ignoreBeforePercent, ignoreAfterPercent);
+
+	const result = { startTime, duration };
+
+	await new Promise((resolve, reject) => {
+		let scale = null;
+
+		if (width && height) {
+			result.width = width | 0;
+			result.height = height | 0;
+			scale = `scale=${width}:${height}`;
+		} else if (width) {
+			result.width = width | 0;
+			result.height = ((info.height * width) / info.width) | 0;
+			scale = `scale=${width}:-1`;
+		} else if (height) {
+			result.height = height | 0;
+			result.width = ((info.width * height) / info.height) | 0;
+			scale = `scale=-1:${height}`;
+		} else {
+			result.width = info.width;
+			result.height = info.height;
+		}
+
+		return ffmpeg()
+			.input(input)
+			.inputOptions([`-ss ${startTime}`])
+			.outputOptions(['-vsync', 'vfr'])
+			.outputOptions(['-q:v', quality, '-vf', scale])
+			.outputOptions([`-t ${fragmentDurationSecond}`])
+			.noAudio()
+			.output(output)
+			.on('start', cmd => log && log({ cmd }))
+			.on('end', resolve)
+			.on('error', reject)
+			.run();
+	});
+
+	return result;
+};
diff --git a/src/api/utils/PreviewUtil.js b/src/api/utils/videoPreview/FrameIntervalPreview.js
index bf3a480..75f6d2b 100644
--- a/src/api/utils/PreviewUtil.js
+++ b/src/api/utils/videoPreview/FrameIntervalPreview.js
@@ -1,8 +1,6 @@
 const ffmpeg = require('fluent-ffmpeg');
 const probe = require('ffmpeg-probe');
 
-const path = require('path');
-
 const noop = () => {};
 
 module.exports = async opts => {
@@ -61,7 +59,7 @@ module.exports = async opts => {
 		ffmpeg(input)
 			.outputOptions(['-vsync', 'vfr'])
 			.outputOptions(['-q:v', quality, '-vf', filter])
-			.outputOption('-an')
+			.noAudio()
 			.outputFormat('webm')
 			.output(output)
 			.on('start', cmd => log && log({ cmd }))