在iOS上导出视频：了解和设置帧持续时间属性？ [英] Exporting videos on iOS: understanding and setting frame duration property?

问题描述

在本教程中合并视频时，作者将导出视频的帧持续时间设置为30 FPS。

In this tutorial on merging videos, the author sets the frame duration for the exported video to 30 FPS.

1）不应将帧持续时间固定为30 FPS，而不应将帧持续时间固定是否与合并后的视频的帧持续时间相关联？

1) Instead of fixing the frame duration to 30 FPS, shouldn't the frame duration be tied to the frame duration of the videos getting merged?

2）导出视频时，对导出的视频使用不同的FPS的优缺点是什么？来自源视频？这是以牺牲视频质量为代价加快出口时间的一种方式吗？例如，如果教程中的源视频是以24 FPS捕获的，那该怎么办？

2) When exporting videos, what are the pros/cons of using a different FPS for the exported video that differs from the source video(s)? Is this one way of speeding up export time at the expense of video quality? For instance, what if the source videos in the tutorial were captured at 24 FPS?

我们需要在iOS上导出视频，有时合并多个视频，有时导出一个视频从相机设备捕获。

We need to export videos on iOS, sometimes merging multiple videos, sometimes exporting a single video captured from the camera device.

推荐答案

1）如果可能，是的。

1) When possible, yes.

2）当源FPS和目标FPS相同时，目标视频将具有更好的质量，并且（最有可能）导出将是更快的过程。

2) When source FPS and target FPS are the same, the target video will have better quality and (most possible) the export will be a faster process.

可以这样想：

当我们有例如24FPS源和24FPS目标，该过程只是获得源帧并产生目标帧。

When we have e.g. 24FPS source and 24FPS target, the process is just getting a source frame and producing a target frame.

当我们有例如24FPS源和30FPS目标，过程将是：

When we have e.g. 24FPS source and 30FPS target, the process will either be:

1. 获得第一帧源 - >第一帧目标，

1. get 1st frame source -> 1st frame target,

第2帧源 - >第2帧目标，

2nd frame source -> 2nd frame target,

第2帧源 - >第3帧目标，

2nd frame source -> 3rd frame target,

第3帧源 - >第4帧目标，依此类推。

3rd frame source -> 4th frame target, and so on.

或

1. 获取第一帧源 - >第一帧目标

1. get 1st frame source -> 1st frame target

将第一帧源与第二帧源混合 - >第二帧目标

blend 1st frame source with 2nd frame source -> 2nd frame target

将第二帧源与第三帧源混合 - >第三帧目标

blend 2nd frame source with 3rd frame source -> 3rd frame target

获得第3帧源 - >第4帧目标，依此类推。

get 3rd frame source -> 4th frame target, and so on.

所以每秒从24帧产生30帧。

so to produce 30 frames from 24 frames for every second.

方法1可能不会受到处理速度的影响，但方法2会因为涉及混合而受到影响。

Method 1 may not suffer in processing speed, but method 2 does because of the blending involved.

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