Unity学习笔记 关于AVPro视频跳转功能(Seeking)的说明

1. Seeking功能的相关接口

通过双精度时间寻找跳转：

• Seek() ⇒ 跳转到精确的指定时间上的画面
• SeekFast() ⇒ 跳转到指定时间上最近的帧画面
• SeekWithTolerance() ⇒ 跳转到指定时间上某个范围时间内的画面（只支持macOS,ios,tvOS）

通过使用帧寻找跳转（只对具有已知恒定帧速率的媒体有效）：

• SeekToFrame() ⇒ 跳转到具体某一帧的画面
• SeekToFrameRelative() ⇒ 跳转到相对于当前帧向前或向后多少帧的画面

底层接口源码如下：

		/// <summary>
		/// The time in seconds seeked will be to the exact time
		/// This can take a long time is the keyframes are far apart
		/// Some platforms don't support this and instead seek to the closest keyframe
		/// </summary>
		void	Seek(double time);

		/// <summary>
		/// The time in seconds seeked will be to the closest keyframe
		/// </summary>
		void	SeekFast(double time);

		/// <summary>
		/// The time in seconds seeked to will be within the range [time-timeDeltaBefore, time+timeDeltaAfter] for efficiency.
		/// Only supported on macOS, iOS and tvOS.
		/// Other platforms will automatically pass through to Seek()
		/// </summary>
		void	SeekWithTolerance(double time, double timeDeltaBefore, double timeDeltaAfter);

		/// <summary>
		/// Seek to a specific frame, range is [0, GetMaxFrameNumber()]
		/// NOTE: For best results the video should be encoded as keyframes only
		/// and have no audio track, or an audio track with the same length as the video track
		/// </summary>
		void	SeekToFrame(int frame, float overrideFrameRate = 0f);

		/// <summary>
		/// Seek forwards or backwards relative to the current frame
		/// NOTE: For best results the video should be encoded as keyframes only
		/// and have no audio track, or an audio track with the same length as the video track
		/// </summary>
		void	SeekToFrameRelative(int frameOffset, float overrideFrameRate = 0f);

需要注意的是，跳转的响应/行为在不同平台会有不同差异

平台	快速近似关键帧搜索(Fast Approximate Keyframe Seeking)	慢速精确寻帧(Slow Accurate Frame Seeking)
Windows (WinRT / Media Foundation)	*	*
Windows (DirectShow)	*	取决于编解码器
Android (ExoPlayer)	*	*
Android (MediaPlayer)	*	API 26 及以上
macOS	*	*
iOS/iPadOS/tvOS	*	*
WebGL	*	视情况而变化

2. 跳转(Seeking)功能的实现案例

具体的实现可以参考AVPro提供的Demo（Demo_MediaPlayer场景）

下面只列出结合时间条(slider)进行视频跳转的部分：

		[Header("UI Components")]
		[SerializeField] Slider _sliderTime = null;

		void Start()
		{
    
			CreateTimelineDragEvents();
		}

		private void CreateTimelineDragEvents()
		{
    
			EventTrigger trigger = _sliderTime.gameObject.GetComponent<EventTrigger>();
			if (trigger != null)
			{
    
				EventTrigger.Entry entry = new EventTrigger.Entry();
				entry.eventID = EventTriggerType.PointerDown;
				entry.callback.AddListener((data) => {
     OnTimeSliderBeginDrag(); });
				trigger.triggers.Add(entry);

				entry = new EventTrigger.Entry();
				entry.eventID = EventTriggerType.Drag;
				entry.callback.AddListener((data) => {
     OnTimeSliderDrag(); });
				trigger.triggers.Add(entry);

				entry = new EventTrigger.Entry();
				entry.eventID = EventTriggerType.PointerUp;
				entry.callback.AddListener((data) => {
     OnTimeSliderEndDrag(); });
				trigger.triggers.Add(entry);

				entry = new EventTrigger.Entry();
				entry.eventID = EventTriggerType.PointerEnter;
				entry.callback.AddListener((data) => {
     OnTimelineBeginHover((PointerEventData)data); });
				trigger.triggers.Add(entry);

				entry = new EventTrigger.Entry();
				entry.eventID = EventTriggerType.PointerExit;
				entry.callback.AddListener((data) => {
     OnTimelineEndHover((PointerEventData)data); });
				trigger.triggers.Add(entry);
			}
		}

		private bool _wasPlayingBeforeTimelineDrag;
		private void OnTimeSliderBeginDrag()
		{
    
			if (_mediaPlayer && _mediaPlayer.Control != null)
			{
    
				_wasPlayingBeforeTimelineDrag = _mediaPlayer.Control.IsPlaying();
				if (_wasPlayingBeforeTimelineDrag)
				{
    
					_mediaPlayer.Pause();
				}
				OnTimeSliderDrag();
			}
		}

		private void OnTimeSliderDrag()
		{
    
			if (_mediaPlayer && _mediaPlayer.Control != null)
			{
    
				TimeRange timelineRange = GetTimelineRange();
				double time = timelineRange.startTime + (_sliderTime.value * timelineRange.duration);
				_mediaPlayer.Control.Seek(time);
				_isHoveringOverTimeline = true;
			}
		}

		private void OnTimeSliderEndDrag()
		{
    
			if (_mediaPlayer && _mediaPlayer.Control != null)
			{
    
				if (_wasPlayingBeforeTimelineDrag)
				{
    
					_mediaPlayer.Play();
					_wasPlayingBeforeTimelineDrag = false;
				}
			}
		}


		private bool _isHoveringOverTimeline;
		private void OnTimelineBeginHover(PointerEventData eventData)
		{
    
			if (eventData.pointerCurrentRaycast.gameObject != null)
			{
    
				_isHoveringOverTimeline = true;
				_sliderTime.transform.localScale = new Vector3(1f, 2.5f, 1f);
			}
		}

		private void OnTimelineEndHover(PointerEventData eventData)
		{
    
			_isHoveringOverTimeline = false;
			_sliderTime.transform.localScale = new Vector3(1f, 1f, 1f);
		}

参考文献

AVPro官方说明文档