FFmpeg混合滤波器始终执行“体积归一化".如何预防它以及它可能有什么弊端? [英] FFmpeg amix-filter always does "volume normalization". How to prevent it and what are the possible drawbacks of it?
问题描述
There are many questions on this topic link1, link2, and link3. However, I am asking for suggestions on the probable solution and if it has some drawbacks.
问题定义: amix-filter始终执行卷标准化"，并且无法关闭
Problem Definition: amix-filter always does "volume normalization" and can't be turned off
参考:请阅读 Reino 上找到.他还在FFmpeg论坛上打开了门票来解释这种情况.
Reference: Please read comments over here by @Reino. He also had opened a ticket on the FFmpeg forum to explain the situation.
棘手的解决方案: amix = inputs = 13:dropout_transition = 1000，volume = 13
Hacky Solution: amix=inputs=13:dropout_transition=1000,volume=13
1)"amix以1/n缩放每个输入的音量，其中n =有效输入的数量.对每个音频帧进行评估.因此，当输入丢失时，剩余的输入将按较小的比例缩放，因此它们的数量会增加."请参阅
1) "amix scales each input's volume by 1/n where n = no. of active inputs. This is evaluated for each audio frame. So when an input drops out, the volume of the remaining inputs is scaled by a smaller amount, hence their volumes increase."Refer
例如，如果我要合并10个音频流，则第一个音频流将按比例缩放1/10，第二按1/9缩放，第3按1/8进行缩放.第9按1/2进行缩放，最后按1进行最后缩放.我是否正确理解了这一点，或者是否想念我想知道的东西?
For example, if I am merging 10 audio streams then, the 1st audio stream will be scaled by 1/10, 2nd by 1/9, 3rd by 1/8 .. 9th by 1/2 and last 10th by 1. Have I understood this correctly or let me know if I am missing something?
2) dropout_transition :，过渡时间，以秒为单位，用于在输入流结束时重新进行音量规范化.默认值为2秒.
2) dropout_transition: The transition time, in seconds, for volume renormalization when an input stream ends. The default value is 2 seconds.
dropout_transition表示它将跳过几秒钟，对吗?因此，如果我设置dropout_transition = 1000(非常大的数字)，则无论视频长度如何，FFmpeg都会在提供的秒数内丢弃/跳过音频过渡.同样，如果我做错了假设，请纠正我.
dropout_transition means it will SKIP given seconds, right? So if I set dropout_transition=1000(very large number) then regardless of video length FFmpeg will drop/skip audio transition for provided seconds. Again, please do correct me if I have made wrong assumption.
3)我已经尝试了许多其他解决方案，但没有任何运气，现在，我非常依赖提供的解决方案.上面的hacky解决方案有什么缺点吗?
3) I have tried many other solutions without any luck and now I am relying profoundly on the provided solution. Is there any drawback to the above hacky solution?
推荐答案
如果我要合并10个音频流，则第一个音频流将按1/10缩放，第二按1/9缩放，按3缩放1/8 .. 9乘1/2，最后10乘1.
不.假设您有4个输入，分别长10、7、4和2秒.让我们将辍学过渡保持为0.然后在开始的2秒钟内，所有输入均处于活动状态，因此每个输入都按1/4缩放.在2到4秒之间，有3个输入处于活动状态，因此所有活动输入(#1、2、3)均按1/3缩放.从4到7秒，只有输入1和2处于活动状态，因此两者均按1/2缩放.从7到10秒，只有输入1处于活动状态，因此它按1进行缩放，即其音量不变.
No. Let's say you have 4 inputs, which are 10, 7, 4 and 2 seconds long respectively. Let's keep dropout transition as 0. Then for first 2 seconds, all inputs are active, so each input is scaled by 1/4. From 2 to 4 seconds, 3 inputs are active, so all active inputs (#1, 2, 3) are scaled by 1/3. From 4 to 7 seconds, only inputs 1 and 2 are active, so both are scaled by 1/2. And from 7 to 10 seconds, only input 1 is active, so it is scaled by 1 i.e. its volume is unchanged.
dropout_transition意味着它会跳过几秒钟，对吧?
不.继续上述情况，假设退出转换为1秒.因此，当输入4结束时，缩放比例不会立即从1/4更改为1/3.它会逐渐过渡1秒以上.
No. Continuing with the above scenario, let's say dropout transition is 1 second. So, when input 4 ends, the scaling does not change from 1/4 to 1/3 immediately. It transitions over 1 second, gradually.
上述hacky解决方案是否有缺点?
在大多数情况下都可以.如果您要合并大声的音乐，则范围会变平，但是在那种情况下没关系.
For most cases, it's fine. If you're combining loud pieces of music, then there will be flattening of range, but it shouldn't matter in that case.
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