does anybody know why dvd use files for audio and video but audio cd's not? What could be the reason for this? e.g. they could make a file for each track and just put them on an audio cd and make cd players compatible with this format. So for me it has always been a mystery why audio cd's work this way. does anybody knows if super audio cd's still work the same as normal ones? 2007/9/13, Josh Coalson <xflac@yahoo.com>:> --- Daniel Aleksandersen <aleksandersen+xiphlists@runbox.com> wrote: > > > Hi list, > > > > I would really like to see support for .cda as input files. The cda > > format is the one used on regular audio CDs. > > if the .cda files appeared as regular files in the filesystem and > implemented enough of the POSIX stream interface, it is possible, > but I don't know the what the format of the data is. > > otherwise, it really doesn't belong in flac but in a ripping program. > > you're the first one to ask though, probably because people using > FLAC also tend to care about rip quality and the .cda scheme > would almost have to use burst mode to present a regular file > interface. > > Josh > > > > > ____________________________________________________________________________________ > Need a vacation? Get great deals > to amazing places on Yahoo! Travel. > http://travel.yahoo.com/ > _______________________________________________ > Flac-dev mailing list > Flac-dev@xiph.org > http://lists.xiph.org/mailman/listinfo/flac-dev >
On Fri, Sep 14, 2007 at 01:10:09AM +0200, Harry Sack wrote:> does anybody know why dvd use files for audio and video but audio cd's not? > What could be the reason for this?the format for CD-ROM sets aside space for error correction and therefore has less available for data. CD audio does not have any error correction, and so has more room for data. Presumably they believed it was better to - accept that errors would get through, and that they would be mostly inaudible - have more space for data, so they could deliver better quality or longer music than they otherwise would - have audio cd readers be simpler, not have to interpret a filesystem format. I don't know but it wouldn't surprise me if the CD-ROM format were an afterthought. Remember, this was the early 80's. Probably the 70's when the design work was done. DVD came on a lot later, with the historical context of CD behind it.> does anybody knows if super audio cd's still work the same as normal ones?no idea.
On Fri, Sep 14, 2007 at 05:35:04PM -0400, Dan Pritts wrote:> the format for CD-ROM sets aside space for error correction and > therefore has less available for data.Red Book CD Audio still has error correction. Otherwise you'd *really* notice the scratches. On Fri, Sep 14, 2007 at 01:10:09AM +0200, Harry Sack wrote:> does anybody know why dvd use files for audio and video but audio cd's not? > What could be the reason for this?Otherwise, yes, as Dan said, The technology is almost 30 years old, and it's designed much more like a digital phonograph than a computer storage disk. CD-DA isn't even block addressable in the normal sense. The data is written in a continuous spiral from start to finish, with local signposts to help seeking. At the time, I expect there was no expectation of using it for data storage, and no need for the overhead of a conventional filesystem. Even DVD-Video only provides the filesystem structure as a convenience. IIRC it's possible to play a dvd by accessing the ifo files at a fixed offset and using the embedded sector references. -r
On Fri, 14 Sep 2007 01:10:09 +0200 "Harry Sack" <tranzedude@gmail.com> wrote:> does anybody know why dvd use files for audio and video but audio cd's not? > What could be the reason for this? > e.g. they could make a file for each track and just put them on an > audio cd and make cd players compatible with this format. So for me it > has always been a mystery why audio cd's work this way.My best guess is that at the time CD audio was designed computers (which had the concept of files and a filesystem) and audio equipment were pretty much separate camps. So when the CD audio format was designed the reference the designers had was the LP record. They made a format that had a continuous stream of data in a spiral around the disk, just like the LP has a continous groove, and which can be divided into "tracks" which hold songs or movements. The new part of the CD format was a way to encode PCM (digital) audio with error correction onto optical media. It was only later that the computer industry realised that the disk could also be used to hold data and, because it was cheap to make and the player technology was well understood, would be economicly viable. So a standard for putting data "sectors" onto the CD media with extra error correction was developed and a corresponding standard for laying out the filesystem within the available storage (ISO 9660). There is also the fact that a CD player was expected to implemented in hardware or with a very simple processor so the format had to be simple. By the time DVD was being designed (and it's subequent sucessors to be) CD-ROM has been around for a while and DVD players were expected to have internal software that could cope with the complexity of working with a filesystem on the disk rather than a simple data stream. Steve.
Hi again list, I have given the matter of supporting .cda as input format some more thought. What I wanted was an easier way to do drag 'n' drop music files from CDs onto the local system and then have those files encoded with FLAC. As of now most operating systems displays files on CDs as .cda. (Which has later been clarified not to even be a format.) I think that what I actually want is for the operating systems to use .flac instead. Similar to what Mac OS X does with .aiff. This should probably have been posted in the advocacy emailing list instead. -- Daniel Aleksandersen
General purpose file systems have disadvantages as well as advantages. For audio-only media, file-based storage would not be as optimal as the way CD audio works. CD was designed with full consideration of how it would be used. Primarily, people put in a piece of music, start at the beginning, and listen until the end. Even if they skip a few tracks here and there, there is still over 99% of the time spent just continuing from where they left off, and less than 1% of the time seeking to some random point. With this in mind, CDDA was designed to make contiguous access most efficient. Not only maximally efficient, but the time delay to find the next audio sample is always constant, without a gap or jump unless the CD is damaged or the user interrupts. CDDA uses a spiral track that is contiguous (and starts near the center of the disc) to enhance the constant access rate. The data is broken into blocks for error correction and other organization reasons, but because the track is spiral, the hardware does not have to seek to find the next block - it is always directly after the previous block. DVD has large sections of contiguous material, but it also has to deal with menus, and even edits to the film for multiple ratings. Because of the variety of data, and the hierarchy of access, and completely new ideas like programmed sequences of media clips, DVD is a more random access media, and it thus forced to use a general- purpose file system. When reading multiple blocks, the hardware must often physically seek the laser to a new position, even if the data is related. You'll note that one of the drawbacks of this design is the layer switch during longer movies which causes a pause in the playback on every DVD player available. We're probably going to see file-based media from here on out, but this comes at a price. I've seen many DVD players "crash" when following the links between menus or media clips. That's because the whole system - from media format to playback system - is more complex, and thus there are more opportunities for things to be misinterpreted. I have never seen a CD player get confused, no matter how complex the programming. There is elegance in simplicity, especially when the simplicity is so closely matched with the way something will be used 99+% of the time. I believe that SACD is also a contiguous spiral of data, but in a different format than CDDA. As far as I know, it is not file based, but is stream based, even on the media itself (apart from low-level blocks for error correction and seeking). Brian Willoughby Sound Consulting On Sep 13, 2007, at 16:10, Harry Sack wrote: does anybody know why dvd use files for audio and video but audio cd's not? What could be the reason for this? e.g. they could make a file for each track and just put them on an audio cd and make cd players compatible with this format. So for me it has always been a mystery why audio cd's work this way. does anybody knows if super audio cd's still work the same as normal ones?