渲染的 AVMutableComposition 中的音频与视频不同步
我有一个带有以下轨道段的 AVMutableComposition：
video:
empty: Y, {{0/1 = 0.000}, {48/100 = 0.480}}
empty: N, {{48/100 = 0.480}, {600/600 = 1.000}}
empty: Y, {{888/600 = 1.480}, {900/600 = 1.500}}
empty: N, {{894/300 = 2.980}, {1040/600 = 1.733}}
audio:
empty: Y, {{0/1 = 0.000}, {48/100 = 0.480}}
empty: N, {{48/100 = 0.480}, {45056/44100 = 1.022}}
empty: Y, {{66224/44100 = 1.502}, {65194/44100 = 1.478}}
empty: N, {{894/300 = 2.980}, {77824/44100 = 1.765}}
计时表示为 CMTimeRange，第一个 CMTime 是开始时间，第二个是期间。换句话说，有两个音频+视频块，它们之前和之间有一些空白的填充空间。
问题是，当我导出此合成并播放导出的视频时，第二个音频片段播放得太早，就好像第二个空填充音频片段在导出过程中被忽略一样。我得到带有正确音频的第一个视频片段，然后立即得到第二个音频片段，然后得到没有音频的第二个视频片段。
可能出什么问题了？
I have an AVMutableComposition with the following track segments:
video:
empty: Y, {{0/1 = 0.000}, {48/100 = 0.480}}
empty: N, {{48/100 = 0.480}, {600/600 = 1.000}}
empty: Y, {{888/600 = 1.480}, {900/600 = 1.500}}
empty: N, {{894/300 = 2.980}, {1040/600 = 1.733}}
audio:
empty: Y, {{0/1 = 0.000}, {48/100 = 0.480}}
empty: N, {{48/100 = 0.480}, {45056/44100 = 1.022}}
empty: Y, {{66224/44100 = 1.502}, {65194/44100 = 1.478}}
empty: N, {{894/300 = 2.980}, {77824/44100 = 1.765}}
The timing is expressed as CMTimeRange, the first CMTime is the start time, the second one is duration. In other words, there are two audio+video chunks with some empty padding space before and between them.
The problem is that when I export this composition and play back the exported video, the second audio segment plays too early, as if the second empty padding audio segment was ignored during the export. I get the first video segment with correct audio, then immediately the second audio segment and then later the second video segment without audio.
What could be wrong?
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问题出在出口上。我使用的是直通导出模式，仅将轨道段复制到结果文件中。我猜时间戳也被简单地复制了，这会导致导出的电影的时间线混乱。将导出模式设置为直通以外的模式可以解决该问题。
The problem was in the export. I was using the pass-through export mode that merely copies the track segments into the resulting file. I guess the time stamps are simply copied, too, which causes a mess in the timeline of the exported movie. Setting the export mode to something else than the pass-through solves the problem.