One thing to consider regarding file formats is the bit depth. In the case of a CD-quality file, it's 16 bits. The sampling rate is fairly meaningless especially when it comes to compressed formats like mp3. One must then consider the compression ratio. for normal AIF and WAV formats, a 16-bit 44.1/48 kHz file is roughly 10 MB per stereo minute whereas a compressed format can be as little as one tenth the size. Higher quality 24-bit files are 50 percent larger at 15 MB per stereo minute. Ultimately, the file size itself needs to be within the 2 GB limit to be useable. I think that's changed in 64-bit systems though. I'll have to double check.
Slau On Mar 12, 2010, at 4:52 PM, Nicolai Svendsen wrote: > Hi, > > Definitely a good post, thank you. > > I was pondering that possibility, though I had a look at two similar files, > one longer than the first. I have a six hour long file, encoded with > 44.100KHZ. That file worked perfectly. Just the way it was supposed to work. > > Then I had a look at the four hour long audio file. Exactly same format and > sample rate. > > So I wrote to the list. I'm still a bit confused as to why it won't, as I > have an even longer file at exactly the same quality that works just fine. > > If you take the audio file at six hours, encoded with a 44100KHZ sample rate. > That's just about 952560000 seconds, or just about. Then take the four hour > long audio file, encoded again at 44100KHZ. That's about 635040000 seconds. > That unfortunately doesn't seem to be the problem. What else might be causing > this? It doesn't even come close to the 2000000000 mark. Only halfway. > > Thank you for the in-depth suggestion, though. :) > > Let me know if I'm understanding this right. > > Regards, > Nic > Skype: Kvalme > MSN Messenger: nico...@home3.gvdnet.dk > AIM: cincinster > yahoo Messenger: cin368 > Facebook Profile > My Twitter > > On Mar 12, 2010, at 10:14 PM, Esther wrote: > >> Hi Nic, >> >> The problem of the maximum time for working with an audio file is not >> specific to iTunes. Basically none of the music programs, including >> QuickTime, can correctly handle sound files where the number of samples >> exceeds 2 billion (or, to be precise, the maximum number that can be >> represented with a 32-bit unsigned integer, or 2 raised to the exponent of >> 31, which is about 2.1478 billion samples). One of the numbers in the file >> header for the audio file is a counter that turns over when you exceed this >> maximum. This means that the actual maximum file length (in time) that can >> be correctly read from these audio files depends on the quality of the file >> encoding. CD quality music files sample the music at 44.1 kHz (44.1 >> thousand samples per second). Voice memo files might sample at 8 kHz (8 >> thousand samples per second) -- a rate that is more than 5 times smaller. >> The total number of samples is the encoding sample rate (e.g. 44.1 kHz for a >> CD) multiplied by the time of your audio file in seconds. This number hits >> the 2 billion maximum for a file length of 13.5 hours, assuming this is >> stereo music. This is an absolute maximum that the file structure can >> correctly represent -- you can still run into problems before this. When >> music programs like QuickTime or any comparable programs on any platform >> (Windows, Linux, Mac, etc.) read these files, they all compute the time from >> the number of samples, and they all get incorrect answers when the counter >> is exceeded. That's why you're able to play the files with QuickLook, which >> just starts streaming without trying to read the time. The exact wrong >> number depends on the rollover value of the counter. >> >> Moreover, if you think back to recent posts by James looking for the intro >> and other music files that the Mac plays on startup, you'll notice that the >> file extensions are .caf instead of .aiff (Audio Interchange File Format). >> The new format is "Core Audio File Format", and one of the reasons for the >> new file format is that these files can correctly represent samples that >> exceed the 2 billion counter maximum. >> >> All of this comes up in discussions of the maximum length you can make a >> single audiobook file and play it correctly. >> >> HTH. You can get longer files to play, and get correct times if you reduce >> the audio quality. >> >> Cheers, >> >> Esther >> >> >> Nicolai Svendsen wrote: >> >>> Hi guys, >>> >>> I sometimes get really huge audio files, sometimes files that last more >>> than eight hours in length. The problem is this. >>> >>> While iTunes can actually measure the time properly, it won't play it all. >>> I have a file which is nine hours long, but it will only play two hours of >>> it. The LCD just stops counting, even though it shows that seven hours are >>> left of the total time. If I use Quick Look, I can go to 100 percent of the >>> file, where iTunes will usually cut it off. However, if I leave it to >>> continue in Quick Look, what will actually happen is that it will go beyond >>> 100 percent because the file is longer than it thinks, even though it >>> actually measures the time properly. I played a similar file earlier today, >>> and it hit 405 percent before it finished, however if I stopped playback or >>> attempted to go backwards, it'd put me back at where it cut off. >>> >>> If anyone can help, I'd appreciate it. And please, don't come with useless >>> comments like "Your iTunes is broken". I know for a fact that it is not, >>> because I just reinstalled out of interest. When I figured out that wasn't >>> the problem, I just reverted the changes. >>> >>> Thanks in advance. :) >>> >>> Regards, >>> Nic >>> Skype: Kvalme >>> MSN Messenger: nico...@home3.gvdnet.dk >>> AIM: cincinster >>> yahoo Messenger: cin368 >>> Facebook Profile >>> My Twitter >>> >>> >> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "MacVisionaries" group. >> To post to this group, send email to macvisionar...@googlegroups.com. >> To unsubscribe from this group, send email to >> macvisionaries+unsubscr...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/macvisionaries?hl=en. > > > -- > You received this message because you are subscribed to the Google Groups > "MacVisionaries" group. > To post to this group, send email to macvisionar...@googlegroups.com. > To unsubscribe from this group, send email to > macvisionaries+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/macvisionaries?hl=en. -- You received this message because you are subscribed to the Google Groups "MacVisionaries" group. 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