Add custom quality factors and quantizer bitrate mode (#448)

* Add custom quality factors and quantizer bitrate mode (closes #327)

* Fix quantizer mode fallback and per-frame quantizer edge cases

* Clean up quantizer mode tests

* Quantizer implementation

* Add quality tests

* Improve conversion codec error message, make test more lenient

* Add quantizer support blog post

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Co-authored-by: Vanilagy <[email protected]>

docs/index.md

@@ -233,14 +233,14 @@ const output = new Output({
 // Add video, driven by a canvas
 const videoSource = new CanvasSource(canvas, {
 	codec: 'av1',
-	bitrate: QUALITY_HIGH,
+	quality: new Quality('high'),
 });
 output.addVideoTrack(videoSource);
 
 // Add audio, driven by audio buffers
 const audioSource = new AudioBufferSource({
 	codec: 'opus',
-	bitrate: QUALITY_HIGH,
+	quality: new Quality('high'),
 });
 output.addAudioTrack(audioSource);