[ lame-Support Requests-3469604 ] Make extant MP3 gapless without lossy reencoding?

Support Requests item #3469604, was opened at 2012-01-04 17:09
Message generated for change (Comment added) made by mike_j_brown
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Category: None
Group: None
Status: Open
Priority: 5
Private: No
Submitted By: noah++ (noahplusplus)
Assigned to: Nobody/Anonymous (nobody)
Summary: Make extant MP3 gapless without lossy reencoding?

Initial Comment:
I have some MP3 files that were either not encoded with LAME or were encoded without gapless options enabled. Is it technically possible for LAME to make these files gapless without lossily reencoding them? If so, is there currently a way for the user to do it?

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Comment By: Mike Brown (mike_j_brown)
Date: 2012-01-05 15:57

Message:
There are two kinds of gapless MP3s. The kind produced by LAME's old
gapless options is just a single stream chopped into sections on frame
boundaries, and you (or the player) are supposed to concatenate them before
or during playback. This technique was largely abandoned before it gained
much traction. The other, currently popular kind is what LAME produces by
default (no special options needed), where each file is a separately
encoded stream, with metadata in it telling the player how many delay &
padding samples to skip on each end to get the part of the stream that
corresponds to the original sample set. This may not be perfectly seamless
but is the definition of gapless that people generally want.

If the encoder was LAME, the encoder delay is known, and for CD-sourced
material (multiples of 588 samples), the padding can be guessed at, or even
confirmed if you have access to the exact track length from the original
CD. Otherwise, there's no way to know for sure. If the encoder is unknown,
then not even the delay is certain. So I don't think there's really a way
to do what you want automatically. Further reading:
http://wiki.hydrogenaudio.org/index.php?title=Gapless_playback

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