AAC / MP4 playback

[wintermute23]

According to the Wiki, Rockbox can play AAC / MP4 files, but (many months ago) I downloaded episodes of a podast in .m4a format which included chapter marks, and I needed to transcode them to MP3 before Rockbox could play them.

Is AAC support moderately new, so that it would be worth trying again? Are only certain file extensions recognised, such that I'd only need to rename the files rather than transcoding them? Are chapter marks in AAC files supported?

Thanks for your help.

[GodEater]

Have you tried searching through the posts in this very forum for posts about AAC playback ?

[wintermute23]

I have been doing that, yes. My research indicates that AAC support was patchy in 2006, chapter support didn't exist in early-mid 2007, and that HE-AAC support is too processor intensive to implement in most targets.

All of which explains why I was having problems back in the day, but doesn't do a great deal to tell me if I'll still have problems if I try again, or what step I can take to work around those problems.

[GodEater]

So you've found that AAC isn't that new at all, not even the chapter support, and that HE-AAC probably won't ever be supported because of how much work it is on the processor.

"Trying Again" would mean what? Downloading a current build, and trying a .aac file with it to see if it's any different. I suspect not as I don't think anyone's done much work on the AAC codec for a while now (other than a few minor bug fixes IIRC).

The only way to "work around" the problem that I can think of would be to use a different codec.

[wintermute23]

So you've found that AAC isn't that new at all, not even the chapter support

What do you mean "chapter support isn't new"? Does that mean that chapter marks are supported now?

"Trying Again" would mean what? Downloading a current build, and trying a .aac file with it to see if it's any different. I suspect not as I don't think anyone's done much work on the AAC codec for a while now (other than a few minor bug fixes IIRC).

It would help if I knew how Rockbox decided which codec to use; does it use a magic number (in which case, file extension is irrelevant), or does it base its decision on the file extension (in which case, changing the extension might just make it work)?

Clearly, I erred in believing that there was a possibility that someone might have been working on what was clearly a known issue. But it's been my experience of Rockbox that it's under active development, and that things can change over the course of a year or two, so I thought I would see if anyone had any more recent information that might prove helpful. Sorry I wasted your time when I should have just assumed that the two-year-old information I'd found would still be relevant.

[Llorean]

Considering the changelog is, has been, and probably always will be available, the information on what has been developed is as available to you as it is to everyone else. Checking if the information is still relevant is as simple as reading about AAC updates in it.

Or simply spending 15 seconds to copy a problematic M4A/MP4/AAC file over and see if it plays. There are many problems still with the AAC codec, and many, many, many, many things that have been fixed. What exactly is problematic about simply spending a few seconds to test it for yourself?

One of the largest remaining problems is simply that files over a certain size will not play. This is probably what you encountered with your podcasts.

[wintermute23]

Considering the changelog is, has been, and probably always will be available, the information on what has been developed is as available to you as it is to everyone else. Checking if the information is still relevant is as simple as reading about AAC updates in it.

The notes on the changelog, while helpful, don't seem to actually answer the questions I have. They're more focused on the technical details of the change that was made, rather than on the ramifications of that change.

Or simply spending 15 seconds to copy a problematic M4A/MP4/AAC file over and see if it plays. There are many problems still with the AAC codec, and many, many, many, many things that have been fixed. What exactly is problematic about simply spending a few seconds to test it for yourself?

Right now, what is problematic is that I'm at work and can't download music files. Rest assured though, when I get home, I plan to spend an hour or so tracking down various AAC files and seeing if I can find any pattern to what works and what doesn't. I was hoping that there would be people here who used played AAC files on a regular basis, or knew a thing or two about their structure, and could offer some advice that would point me ni the right direction. I often find that asking a couple of questions can save me a fair amount of time further down the road.

One of the largest remaining problems is simply that files over a certain size will not play. This is probably what you encountered with your podcasts.

That sounds plausible. As I recall, they were approximately 15-20 minutes in length. Thanks for the help.

[Lear]

What do you mean "chapter support isn't new"? Does that mean that chapter marks are supported now?

No, chapter marks aren't supported. However, a bookmarked file (typically with the extension .m4b, I think) should be playable.

It would help if I knew how Rockbox decided which codec to use; does it use a magic number (in which case, file extension is irrelevant), or does it base its decision on the file extension (in which case, changing the extension might just make it work)?

Rockbox mainly uses the extension, though in some cases additional information is used (e.g., to separate between ALAC and AAC). For AAC, Rockbox supports .m4a, .m4b and .mp4.

That sounds plausible. As I recall, they were approximately 15-20 minutes in length. Thanks for the help.

Though 15-20 minutes long files shouldn't be a problem (very old versions of Rockbox might fail though). However, it is difficult to say for sure, as it depends on the structure of certain parts of the metadata in the file...

If you use an "optimized" MP4 file (Foobar has a function for that), Rockbox should be able to handle at least 90 minutes long tracks, if I recall correctly.