Shaka Player 파헤치기 - 화질 변경 방식 분석#

1// 재생 가능한 Variant 목록에서 1080p를 찾아 선택
2const tracks = player.getVariantTracks();
3const target = tracks.find((t) => t.height === 1080);
4
5player.selectVariantTrack(target);

1// player.js — selectVariantTrack
2selectVariantTrack(track, clearBuffer = false, safeMargin = 0) {

1// player.js — selectVariantTrack JSDoc (발췌)
2// Changing variants will take effect once the currently buffered content has
3// been played. To force the change to happen sooner, use
4// clearBuffer with safeMargin. Setting clearBuffer to true will clear all
5// buffered content after safeMargin, allowing the new variant to start
6// playing sooner.

1// player.js — selectVariantTrack (발췌)
2this.switchVariant_(
3    variant, /* fromAdaptation= */ false,
4    clearBuffer || false, safeMargin || 0);

1// media/streaming_engine.js — switchInternal_ (발췌)
2if (clearBuffer) {
3  if (mediaState.clearingBuffer) {
4    // 이미 버퍼를 비우는 중이면, flush만 확실히 하도록 표시
5    mediaState.waitingToFlushBuffer = true;
6  } else if (mediaState.performingUpdate) {
7    // 업데이트(세그먼트 fetch) 중이면 끝난 뒤 비우도록 예약
8    mediaState.waitingToClearBuffer = true;
9    mediaState.clearBufferSafeMargin = safeMargin;
10    mediaState.waitingToFlushBuffer = true;
11  } else {
12    // 진행 중인 타이머를 취소하고 즉시 버퍼를 비운다
13    this.cancelUpdate_(mediaState);
14    this.clearBuffer_(mediaState, /* flush= */ true, safeMargin)
15        .catch((error) => { /* ... */ });
16  }
17} else {
18  if (!mediaState.performingUpdate && !mediaState.updateTimer) {
19    this.scheduleUpdate_(mediaState, 0);
20  }
21}

1// player.js — selectVariantTrack (발췌)
2const active = this.streamingEngine_.getCurrentVariant();
3if (this.config_.abr.enabled && (active.video != variant.video ||
4    (active.audio && variant.audio &&
5    active.audio.language == variant.audio.language &&
6    active.audio.channelsCount == variant.audio.channelsCount &&
7    active.audio.label == variant.audio.label))) {
8  shaka.log.alwaysWarn('Changing tracks while abr manager is enabled ' +
9                       'will likely result in the selected track ' +
10                       'being overridden. Consider disabling abr ' +
11                       'before calling selectVariantTrack().');
12}

1// ABR을 끄고 화질을 고정한 뒤 전환
2player.configure({ abr: { enabled: false } });
3
4const target = player.getVariantTracks().find((t) => t.height === 1080);
5player.selectVariantTrack(target, /* clearBuffer= */ true);

1// player.js — applyConfig_ (발췌)
2if (this.abrManager_) {
3  this.abrManager_.configure(this.config_.abr);
4  // 여러 번 호출해도 효과는 동일하므로 매번 enable/disable을 반영
5  if (this.config_.abr.enabled) {
6    this.abrManager_.enable();
7  } else {
8    this.abrManager_.disable();
9  }
10  this.onAbrStatusChanged_();
11}

1// 720p(1280x720) 이하로만 재생하도록 상한을 건다 (ABR은 켜둔 채)
2player.configure({
3  restrictions: {
4    maxWidth: 1280,
5    maxHeight: 720,
6  },
7});

1// player.js — applyConfig_ (발췌)
2// 제약(restrictions)을 다시 적용한다
3if (this.manifestFilterer_.filterManifestWithRestrictions(this.manifest_)) {
4  this.onTracksChanged_();
5}
6
7if (this.abrManager_) {
8  // 새 설정에 맞춰 ABR 후보 Variant를 갱신
9  this.updateAbrManagerVariants_();
10}
11
12// 재생 중인 스트림이 제약에 걸렸다면 새 Variant로 전환
13const activeVariant = this.streamingEngine_.getCurrentVariant();
14if (activeVariant) {
15  if (!activeVariant.allowedByApplication ||
16      !activeVariant.allowedByKeySystem) {
17    shaka.log.debug('Choosing new variant after changing configuration');
18    this.chooseVariantAndSwitch_();
19  }
20}

1// util/stream_utils.js — applyRestrictions (발췌)
2for (const variant of variants) {
3  const originalAllowed = variant.allowedByApplication;
4  variant.allowedByApplication = shaka.util.StreamUtils.meetsRestrictions(
5      variant, restrictions, maxHwRes);
6
7  if (originalAllowed != variant.allowedByApplication) {
8    tracksChanged = true;
9  }
10}

1// util/stream_utils.js — meetsRestrictions (발췌)
2const inRange = (x, min, max) => x >= min && x <= max;
3
4if (variant && variant.video &&
5    variant.video.width && variant.video.height) {
6  let videoWidth = variant.video.width;
7  let videoHeight = variant.video.height;
8  if (videoHeight > videoWidth) {
9    // 세로 영상이면 가로/세로를 뒤집어 비교
10    [videoWidth, videoHeight] = [videoHeight, videoWidth];
11  }
12
13  if (!inRange(videoWidth,
14      restrictions.minWidth,
15      Math.min(restrictions.maxWidth, maxHwRes.width))) {
16    return false;
17  }
18
19  if (!inRange(videoHeight,
20      restrictions.minHeight,
21      Math.min(restrictions.maxHeight, maxHwRes.height))) {
22    return false;
23  }
24  // ... minPixels/maxPixels, frameRate, channelsCount, bandwidth 검사 ...
25}