add keyFrameInterval to ConversionVideoOptions

docs/guide/converting-media-files.md

@@ -124,6 +124,7 @@ type ConversionVideoOptions = {
 	codec?: VideoCodec;
 	bitrate?: number | Quality;
 	alpha?: 'discard' | 'keep'; // Defaults to 'discard'
+	keyFrameInterval?: number;
 	forceTranscode?: boolean;
 };
 ```
@@ -180,7 +181,9 @@ Use the `codec` property to control the codec of the output track. This should b
 
 Use the `bitrate` property to control the bitrate of the output video. For example, you can use this field to compress the video track. Accepted values are the number of bits per second or a [subjective quality](./media-sources#subjective-qualities). If this property is set, transcoding will always happen. If this property is not set but transcoding is still required, `QUALITY_HIGH` will be used as the value.
 
-If you want to prevent direct copying of media data and force a transcoding step, use `forceTranscode: true`.
+Use the `keyFrameInterval` property to control the interval in seconds between key frames in the output video.
+
+If you want to prevent direct copying of media data and force a transcoding step, use `forceTranscode: true`. Setting `keyFrameInterval` or `frameRate` will automatically force transcoding, even if `forceTranscode` is not explicitly set to `true`.
 
 ## Audio options
 

src/conversion.ts

@@ -166,6 +166,11 @@ export type ConversionVideoOptions = {
 	 * VP9.
 	 */
 	alpha?: 'discard' | 'keep';
+	/**
+	 * The desired interval in seconds between key frames in the output video.
+	 * Setting this value will force transcoding (even if `forceTranscode` is not explicitly set to `true`).
+	 */
+	keyFrameInterval?: number;
 	/** When `true`, video will always be re-encoded instead of directly copying over the encoded samples. */
 	forceTranscode?: boolean;
 };
@@ -252,6 +257,12 @@ const validateVideoOptions = (videoOptions: ConversionVideoOptions | undefined)
 	if (videoOptions?.alpha !== undefined && !['discard', 'keep'].includes(videoOptions.alpha)) {
 		throw new TypeError('options.video.alpha, when provided, must be either \'discard\' or \'keep\'.');
 	}
+	if (
+		videoOptions?.keyFrameInterval !== undefined
+		&& (!Number.isFinite(videoOptions.keyFrameInterval) || videoOptions.keyFrameInterval <= 0)
+	) {
+		throw new TypeError('options.video.keyFrameInterval, when provided, must be a finite positive number.');
+	}
 };
 
 const validateAudioOptions = (audioOptions: ConversionAudioOptions | undefined) => {
@@ -775,7 +786,8 @@ export class Conversion {
 		const needsTranscode = !!trackOptions.forceTranscode
 			|| this._startTimestamp > 0
 			|| firstTimestamp < 0
-			|| !!trackOptions.frameRate;
+			|| !!trackOptions.frameRate
+			|| trackOptions.keyFrameInterval !== undefined;
 		let needsRerender = width !== originalWidth
 			|| height !== originalHeight
 			|| (totalRotation !== 0 && !outputSupportsRotation)
@@ -858,6 +870,7 @@ export class Conversion {
 			const encodingConfig: VideoEncodingConfig = {
 				codec: encodableCodec,
 				bitrate,
+				keyFrameInterval: trackOptions.keyFrameInterval,
 				sizeChangeBehavior: trackOptions.fit ?? 'passThrough',
 				alpha,
 				onEncodedPacket: sample => this._reportProgress(track.id, sample.timestamp + sample.duration),