# CD/DVD usage

## CD/DVD drives

Modern CD-ROM drives can attain very high head speeds, yet some CD-ROM drives are capable of running at reduced speeds. There are several reasons that might make you consider changing the speed of a CD-ROM drive:

- There have been reports of read errors at high speeds, especially with badly pressed CD-ROMs. Reducing the speed can prevent data loss under these circumstances.

- Many CD-ROM drives are annoyingly loud, a lower speed may reduce the noise.

### Linux

You can reduce the speed of IDE CD-ROM drives with `hdparm`, `setcd` or `cdctl`. It works like this:

    hdparm -E [speed] [cdrom device]

    setcd -x [speed] [cdrom device]

    cdctl -bS [speed]

If you are using SCSI emulation, you might have to apply the settings to the real IDE device, not the emulated SCSI device.

If you have root privileges the following command may also help:

    echo file_readahead:2000000 > /proc/ide/[cdrom device]/settings

This sets prefetched file reading to 2MB, which helps with scratched CD-ROMs. If you set it to too high, the drive will continuously spin up and down, and will dramatically decrease the performance. It is recommended that you also tune your CD-ROM drive with `hdparm`:

    hdparm -d1 -a8 -u1 [cdrom device]

This enables DMA access, read-ahead, and IRQ unmasking (read the `hdparm` man page for a detailed explanation).

Please refer to "`/proc/ide/[cdrom device]/settings`" for fine-tuning your CD-ROM.

SCSI drives do not have a uniform way of setting these parameters (Do you know one? Tell us!) There is a tool that works for Plextor SCSI drives.

### FreeBSD

speed:

    cdcontrol [-f device] speed [speed]

DMA:

    sysctl hw.ata.atapi_dma=1

## DVD playback

For the complete list of available options, please read the man page. The syntax to play a standard DVD is as follows:

    mplayer dvd://<track> [-dvd-device <device>]

Example:

    mplayer dvd://1 -dvd-device /dev/hdc

If you have compiled MPlayer with dvdnav support, the syntax is the same, except that you need to use dvdnav:// instead of dvd://.

The default DVD device is `/dev/dvd`. If your setup differs, make a symlink or specify the correct device on the command line with the `-dvd-device` option.

MPlayer uses libdvdread and libdvdcss for DVD playback and decryption. These two libraries are contained in the `libmpdvdkit2` subdirectory of the MPlayer source tree, you do not have to install them separately. You can also use system-wide versions of the two libraries, but this solution is not recommended, as it can result in bugs, library incompatibilities and slower speed.

In case of DVD decoding problems, try disabling supermount, or any other such facilities. Some RPC-2 drives may also require setting the region code.

DVD structure

DVD disks have 2048 bytes per sector with ECC/CRC. They usually have an UDF filesystem on a single track, containing various files (small .IFO and .BUK files and big (1GB) .VOB files). They are real files and can be copied/played from the mounted filesystem of an unencrypted DVD.

The .IFO files contain the movie navigation information (chapter/title/angle map, language table, etc) and are needed to read and interpret the .VOB content (movie). The .BUK files are backups of them. They use sectors everywhere, so you need to use raw addressing of sectors of the disc to implement DVD navigation or decrypt the content.

DVD support needs raw sector-based access to the device. Unfortunately you must (under Linux) be root to get the sector address of a file. That's why we don't use the kernel's filesystem driver at all, instead we reimplement it in userspace. libdvdread 0.9.x and libmpdvdkit do this. The kernel UDF filesystem driver is not needed as they already have their own builtin UDF filesystem driver. Also the DVD does not have to be mounted as only the raw sector-based access is used.

Sometimes `/dev/dvd` cannot be read by users, so the libdvdread authors implemented an emulation layer which transfers sector addresses to filenames+offsets, to emulate raw access on top of a mounted filesystem or even on a hard disk.

libdvdread even accepts the mountpoint instead of the device name for raw access and checks `/proc/mounts` to get the device name. It was developed for Solaris, where device names are dynamically allocated.

The default DVD device is `/dev/dvd`. If your setup differs, make a symlink, or specify the correct device on the command line with the `-dvd-device` option.

DVD decryption

DVD decryption is done by libdvdcss. The method can be specified through the `DVDCSS_METHOD` environment variable, which can be set to key, disk or title.

If nothing is specified it tries the following methods (default: key, title request):

1. bus key: This key is negotiated during authentication (a long mix of ioctls and various key exchanges, crypto stuff) and is used to encrypt the title and disk keys before sending them over the unprotected bus (to prevent eavesdropping). The bus key is needed to get and predecrypt the crypted disk key.

2. cached key: MPlayer looks for already cracked title keys which are stored in the `~/.dvdcss` directory (fast).

3. key: If no cached key is available, MPlayer tries to decrypt the disk key with a set of included player keys.

4. disk: If the key method fails (e.g. no included player keys), MPlayer will crack the disk key using a brute force algorithm. This process is CPU intensive and requires 64 MB of memory (16M 32Bit entries hash table) to store temporary data. This method should always work (slow).

5. title request: With the disk key MPlayer requests the crypted title keys, which are inside hidden sectors using ioctl(). The region protection of RPC-2 drives is performed in this step and may fail on such drives. If it succeeds, the title keys will be decrypted with the bus and disk key.

6. title: This method is used if the title request failed and does not rely on any key exchange with the DVD drive. It uses a crypto attack to guess the title key directly (by finding a repeating pattern in the decrypted VOB content and guessing that the plain text corresponding to the first encrypted bytes is a continuation of that pattern). The method is also known as "known plaintext attack" or "DeCSSPlus". In rare cases this may fail because there is not enough encrypted data on the disk to perform a statistical attack or because the key changes in the middle of a title. This method is the only way to decrypt a DVD stored on a hard disk or a DVD with the wrong region on an RPC2 drive (slow).

RPC-1 DVD drives only protect region settings through software. RPC-2 drives have a hardware protection that allows 5 changes only. It might be needed/recommended to upgrade the firmware to RPC-1 if you have a RPC-2 DVD drive. You can try finding firmware upgrades for your drive on the internet, this firmware forum may be a good starting point for your search. If there is no firmware upgrade available for your device, use the regionset tool to set the region code of your DVD drive (under Linux). Warning: You can only set the region 5 times.

## VCD playback

For the complete list of available options, please read the man page. The Syntax for a standard Video CD (VCD) is as follows:

    mplayer vcd://<track> [-cdrom-device <device>]

Example:

    mplayer vcd://2 -cdrom-device /dev/hdc

The default VCD device is `/dev/cdrom`. If your setup differs, make a symlink or specify the correct device on the command line with the `-cdrom-device` option.

At least Plextor and some Toshiba SCSI CD-ROM drives have horrible performance reading VCDs. This is because the CDROMREADRAW ioctl is not fully implemented for these drives. If you have some knowledge of SCSI programming, please help us implement generic SCSI support for VCDs.

In the meantime you can extract data from VCDs with readvcd and play the resulting file with MPlayer.

VCD structure

A Video CD (VCD) is made up of CD-ROM XA sectors, i.e. CD-ROM mode 2 form 1 and 2 tracks:

- The first track is in mode 2 form 2 format which means it uses L2 error correction. The track contains an ISO-9660 filesystem with 2048 bytes/sector. This filesystem contains VCD metadata information, as well as still frames often used in menus. MPEG segments for menus can also be stored in this first track, but the MPEGs have to be broken up into a series of 150-sector chunks. The ISO-9660 filesystem may contain other files or programs that are not essential for VCD operation.

- The second and remaining tracks are generally raw 2324 bytes/sector MPEG (movie) tracks, containing one MPEG PS data packet per sector. These are in mode 2 form 1 format, so they store more data per sector at the loss of some error correction. It is also legal to have CD-DA tracks in a VCD after the first track as well. On some operating systems there is some trickery that goes on to make these non-ISO-9660 tracks appear in a filesystem. On other operating systems like GNU/Linux this is not the case (yet). Here the MPEG data cannot be mounted. As most movies are inside this kind of track, you should try `vcd://2` first.

- There exist VCD disks without the first track (single track and no filesystem at all). They are still playable, but cannot be mounted.

- The definition of the Video CD standard is called the Philips "White Book" and it is not generally available online as it must be purchased from Philips. More detailed information about Video CDs can be found in the vcdimager documentation.

About .DAT files

The ~600 MB file visible on the first track of the mounted VCD is not a real file! It is a so called ISO gateway, created to allow Windows to handle such tracks (Windows does not allow raw device access to applications at all). Under Linux you cannot copy or play such files (they contain garbage). Under Windows it is possible as its iso9660 driver emulates the raw reading of tracks in this file. To play a .DAT file you need the kernel driver which can be found in the Linux version of PowerDVD. It has a modified iso9660 filesystem (`vcdfs/isofs-2.4.X.o`) driver, which is able to emulate the raw tracks through this shadow .DAT file. If you mount the disc using their driver, you can copy and even play .DAT files with MPlayer. But it will not work with the standard iso9660 driver of the Linux kernel! Use `vcd://` instead. Alternatives for VCD copying are the new cdfs kernel driver (not part of the official kernel) that shows CD sessions as image files and cdrdao, a bit-by-bit CD grabbing/copying application.