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Old 22nd May 2018, 13:30   #14661  |  Link
sneaker_ger
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Like many other codecs AC3 hs fixed-length frames and encoder delay. One AC3 frame is 1536 samples long so at 48 kHz you have a frame-length of 32 ms. That will be the same with every AC3 encoder. Either work in WAV format incl. the append operation and encode after or at least try to find a better (e.g. silent) spot where you can append better.
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Old 22nd May 2018, 13:40   #14662  |  Link
Music Fan
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Mmh, thanks for the explanation but that's what I didn't want to read
It's strange because I cut an ac3 file in 2 parts (with mkvmerge), I modified the first (a few seconds), re-encoded it in ac3 and the silence appeared at the end.
Normally, mkvmerge can't cut in the middle of an AC3 frame, thus the new ac3 file should be as the first (a multiple of 1536 samples).
I will verify if I can add silence at the beginning (which would not be problematic in this case) to get a size being a multiple of 1536 samples.
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Old 22nd May 2018, 13:42   #14663  |  Link
sneaker_ger
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With AC3 we usually have 5ms encoder delay. It would fit your 27ms because 32ms-5ms = 27ms. So maybe remove 5ms in the beginning.

eac3to input.wav output.ac3 -5ms
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Old 22nd May 2018, 15:33   #14664  |  Link
Music Fan
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It's better, but there is still a 1ms silence at the end (and the same with -6ms). I will try it and see if I hear it.
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Old 22nd May 2018, 17:15   #14665  |  Link
Music Fan
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I don't hear anymore the gap with a 1ms silence.
But curiously, I had also tried to create a wav being a multiple of 1536 samples and eac3to still added a silence (a few ms) at the end.
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