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If you're converting .aax files you should consider using .m4b as the output, since it preserves chapters and remembers your last listened timestamp [0]: > Aud

If you're converting .aax files you should consider using .m4b as the output, since it preserves chapters and remembers your last listened timestamp [0]: > Audiobook and podcast files, which also contain metadata including chapter markers, images, and hyperlinks, can use the extension .m4a, but more commonly use the .m4b extension. An .m4a audio file cannot "bookmark" (remember the last listening spot), whereas .m4b extension files can. The cool thing is that once you rip your activation bytes, it works for all your audiobooks. Would definitely recommend it. [0] https://en.wikipedia.org/wiki/MPEG-4_Part_14 https://en.wikipedia.org/wiki/MPEG-4_Part_14

Youden 6y ago
I don't think that's quite accurate. There's no functional difference between a .m4b file and a .m4a file. Both use the MP4 container so adhere to the same specification, so support all the same features (including bookmarks). FFmpeg even uses the same muxer and demuxer for both "formats". The only difference is a non-standard convention used by certain software (like iTunes) to write autiobook-related metadata only to MP4 files that use the .m4b file extension. You'll get exactly the same result if you just change the file extension after remuxing/transcoding.
- danudey 6y ago
  Well, it's also worth noting that different file extensions can have different associations, so .m4b is more likely to open in an app that the user wants to use for audiobooks, rather than opening in a generic mp4 audio playing app. Even iTunes, I think, would treat files differently between m4r (Ringtone) and m4a (audio) files, so despite there being no difference at all, using the 'correct' extension might be quite a bit more convenient in the long run.
  - Youden 6y ago
    This is true and I'm not saying you shouldn't use the .m4b extension, I just want to make it clear that that's the only difference. A ".m4b file" is just an MP4 with a funny file extension.
  - encom 6y ago
    >Even iTunes, I think, would treat files differently[...] Yes, because it's Apple (of course) who started using non-standard .m4a, .m4b and .m4r extensions, instead of the standard .mp4.
    - LocalH 6y ago
      I don’t see a problem with .m4a and .m4v for standalone streams of AAC and AVC respectively.
- apetresc 6y ago
  Wait, so an m4b stores playback position in the file itself? As in, the checksum will change and file syncers like Syncthing will re-upload every time I hit pause?
  - pwinnski 6y ago
    audiobook-related metadata does not include the current play position, in this case. It includes things like author and editor and narrator.
  - encom 6y ago
    No, that's entirely player-specific and has nothing to do with the MP4 format at all.
  - majewsky 6y ago
    I don't know Syncthing internals, but state of the art in file syncing is to use rolling checksums to identify which parts of the file have changed. If only a few bytes of the file are overwritten, only the immediate vicinity of these bytes would be synced.
anderspitman 6y ago
So it writes the timestamp to the file metadata? That would cause issues with syncing, backups, running from a read-only filesystem, etc. My audiobook app already keeps track of current timestamp for me.
- sbierwagen 6y ago
  And where does the audiobook app store the current timestamp?
  - anderspitman 6y ago
    Probably in the app data directory, which I prefer.
- xsmasher 6y ago
  it sounds like .m4b is just a flag that tells the player "treat this as a book, not a music file"
Florin_Andrei 6y ago
Isn't bookmarking a job for the player? Then it shouldn't matter what file type you use.
teilo 6y ago
The information online about M4A vs M4B is wrong. There is no difference other than the file extension. The Wikipedia article links to a lifewire.com article about the bookmark claim. This container format can store XMP metadata, and you can certainly have a player that saves a playback position in the file's XMP metadata, regardless of its M4A or M4B extension. But every player I know of doesn't do that. They store playback positions in their own internal database. This claim seems to originate from the fact that the old iPods only remembered the last played position on M4B files. But that's entirely a player convention, not a file format convention.

Youden 6y ago

I don't think that's quite accurate. There's no functional difference between a .m4b file and a .m4a file. Both use the MP4 container so adhere to the same specification, so support all the same features (including bookmarks). FFmpeg even uses the same muxer and demuxer for both "formats". The only difference is a non-standard convention used by certain software (like iTunes) to write autiobook-related metadata only to MP4 files that use the .m4b file extension. You'll get exactly the same result if you just change the file extension after remuxing/transcoding.

danudey 6y ago
Well, it's also worth noting that different file extensions can have different associations, so .m4b is more likely to open in an app that the user wants to use for audiobooks, rather than opening in a generic mp4 audio playing app. Even iTunes, I think, would treat files differently between m4r (Ringtone) and m4a (audio) files, so despite there being no difference at all, using the 'correct' extension might be quite a bit more convenient in the long run.
- Youden 6y ago
  This is true and I'm not saying you shouldn't use the .m4b extension, I just want to make it clear that that's the only difference. A ".m4b file" is just an MP4 with a funny file extension.
- encom 6y ago
  >Even iTunes, I think, would treat files differently[...] Yes, because it's Apple (of course) who started using non-standard .m4a, .m4b and .m4r extensions, instead of the standard .mp4.
  - LocalH 6y ago
    I don’t see a problem with .m4a and .m4v for standalone streams of AAC and AVC respectively.
apetresc 6y ago
Wait, so an m4b stores playback position in the file itself? As in, the checksum will change and file syncers like Syncthing will re-upload every time I hit pause?
- pwinnski 6y ago
  audiobook-related metadata does not include the current play position, in this case. It includes things like author and editor and narrator.
- encom 6y ago
  No, that's entirely player-specific and has nothing to do with the MP4 format at all.
- majewsky 6y ago
  I don't know Syncthing internals, but state of the art in file syncing is to use rolling checksums to identify which parts of the file have changed. If only a few bytes of the file are overwritten, only the immediate vicinity of these bytes would be synced.

anderspitman 6y ago

So it writes the timestamp to the file metadata? That would cause issues with syncing, backups, running from a read-only filesystem, etc. My audiobook app already keeps track of current timestamp for me.

sbierwagen 6y ago
And where does the audiobook app store the current timestamp?
- anderspitman 6y ago
  Probably in the app data directory, which I prefer.
xsmasher 6y ago
it sounds like .m4b is just a flag that tells the player "treat this as a book, not a music file"

Florin_Andrei 6y ago

Isn't bookmarking a job for the player? Then it shouldn't matter what file type you use.

teilo 6y ago

The information online about M4A vs M4B is wrong. There is no difference other than the file extension. The Wikipedia article links to a lifewire.com article about the bookmark claim. This container format can store XMP metadata, and you can certainly have a player that saves a playback position in the file's XMP metadata, regardless of its M4A or M4B extension. But every player I know of doesn't do that. They store playback positions in their own internal database. This claim seems to originate from the fact that the old iPods only remembered the last played position on M4B files. But that's entirely a player convention, not a file format convention.