File Size Reduce After Processing Metadata

I was wondering if anyone has experience a decrease in the file size due to processing in Picard? I add all of the metadata to an album and then save. It outputs an album where each song is a smaller file size than where it started. I am so confused as to why there is a decrease at all but in some instances, 8-10 megabytes. Any clarification on this would be greatly appreciated. Thank you!!!

EDIT: 0.8 megabytes to 1 megabyte.

Some audio formats have space reserved for metadata (that’s called padding), on save this space can be reduced if far too big. I guess that’s what happening in your case.

See Tag Padding — mutagen
and Add a way to reduce the padding after writing tags · Issue #229 · quodlibet/mutagen · GitHub

Also images embedded in your tags depends on many parameters, including Picard options, and size of metadata can vary a lot, it often leads to change in padding for formats supporting it (increase or decrease).


Hello, @bluenot3, and welcome to GnuCash!

Picard is supposed to change the metadata embedded in a music file, but not change the audio content. Most of the metadata is compact, a few thousand bytes or so. The bulkiest thing is likely to be embedded cover art, at a few megabytes. Most of the size of an digital music file is taken up with the audio data.

It is possible that if you have a digital music file with several cover art images embedded, and you have Picard set up so that it strips out embedded cover art, you might possibly come up with an size reduction of a few megabytes. And, as @Zas points out, the music file could include padding, which Picard removes.

Still, 8-10 megabytes is a lot for just a metadata change. Is that the size change per file, or the total size change for all the album’s music files put together?


Just to clarify further, IMO:

  1. Picard does not do anything to a file unless you decide to save new metadata, and it is only when it is already writing changes that it may delete embedded cover art or metadata padding and get you the disk space back.

  2. Picard itself does not do anything to remove excess metadata padding - this is a function of the tagging library code that Picard uses. I am not sure whether the library has any controls to say what should happen to excess metadata padding in the event that there is a valid use case for disabling its removal.

  3. Since this is literally wasted disk space on your HDD or SDD or Flash drive, most people would agree that it is a good thing to get it back as free space.


It’s also possible that tag fields contained more letters before Picard was used.

Other than that, check out the option:

Thank you very much for the reply and for providing some links for me to check out. I will look into this and it looks like it may very well be the case. Thank you!

I made an edit on my post. I made a type. It was supposed to be 0.8 mb to 1 mb ( in the case of a slightly larger file). The padding was not something that I was aware of and will be looking into that and testing the waters to see if that might be the issue. Thank you for your reply to my post.

I definitely see the benefit of removing that padding. I just did not know that was a thing. So when I saw my file sizes reducing, it worried me and I did not want to proceed further with Picard until I figured it out. Once I can confirm that it is indeed just removing padding and/or doing something pertaining to the cover art, I will most likely proceed with Picard for the rest of my library processing.

Just curious why you recommend checking that box. I looked on the internet and ID3v1 → " The v1 tag allows 30 bytes each for the title, artist, album, and a “comment”, 4 bytes for the year, and 1 byte to…"

That seems like it would add more unnecessary data, wouldn’t it?

You are unlikely to want to bother with ID3v1 unless you have some very very old MP3 players. That was very limited in what data it can hold. Far better to aim for ID3v2 v2.4

A simple way of comparing your music is install Audacity. Then you can load the before and after files into that music editor and you would see the exact same waveform of the music.


I don’t recommend this.

I recommended you check that if you accidentally unchecked this option, the file size decreased and you didn’t know about it.


check, examine, inspect, not mark

I am slightly embarrassed to report my solution/findings for this. As it turns out, Picard will remove the album art and replace it with something smaller. The file size difference that I am seeing is in fact the difference in file size to a smaller image


Thank you for telling us how the story ended!

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