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mvOpen(3dm)							   mvOpen(3dm)

NAME    [Toc]    [Back]

     mvOpenFile, mvOpenFD, mvOpenMem - open movie instances

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/moviefile.h>

     DMstatus mvOpenFile( const	char* fileName,	int oflag, MVid* returnMovie )

     DMstatus mvOpenFD(	int fd,	MVid* returnMovie )

     DMstatus mvOpenMem( void* pointer,	size_t size, MVid* returnMovie )

DESCRIPTION    [Toc]    [Back]

     mvOpenFile, mvOpenFD, and mvOpenMem read an existing movie	and create a
     movie instance in memory that holds information about it. A movie
     instance is a handle that allows you to read, write, edit,	and play a
     movie file.  It contains information about	the different tracks in	a
     movie.  These operations are defined for three different storage media
     (file name, file descriptor, and memory).

     mvOpenFile	is used	to read	files on disk. fileName	gives the name of the
     file to open, and oflag must have either O_RDONLY (for read-only access)
     or	O_RDWR (for read/write access) masked in. MPEG files may take
     additional	flags masked into the oflag parameter, to determine whether
     the MPEG file should be prescanned	or not (MV_MPEG1_PRESCAN_OFF), and to
     determine the decimation factor of	the audio

     Note that MPEG files will have a default audio decimation factor of a
     quarter. As such the sampling rate	will be	set to a quarter of its
     original value. The full bandwidth	flag must be used if audio quality is
     to	be played at the same quality of its original recording.

     Note that in some circumstances, even if a	movie is opened	O_RDWR,	the
     Movie File	Library	may still only be able to perform read accesses	on it.
     Reasons for this include incomplete support of certain file formats or
     lack of necessary compression functionality.  mvIsReadOnly(3dm) should be
     called after a movie has been opened to determine whether or not actions
     which modify the movie will be allowed.

     mvOpenFD is used to open a	movie from a file descriptor.  Using file
     descriptors allows	movies to be embedded within other files.  For
     example, a	movie file might be embedded in	the file of a word-processing
     program.  When the	word processing	program	is ready to access the movie,
     it	seeks to the position of the movie within its file and passes the file
     descriptor	(fd) to	the movie library.

     mvOpenMem opens a movie of	size size at location pointer from memory.

									Page 1

mvOpen(3dm)							   mvOpen(3dm)

     mvOpenFile, mvOpenFD, and mvOpenMem all return the	identifier for the new
     movie in returnMovie.  If everything goes well they return	DM_SUCCESS,
     otherwise DM_FAILURE is returned.

NOTES    [Toc]    [Back]

     Movies consist of two parts: the actual frames (called data), and the
     information used to reference those frames	(called	metadata).  In movie
     files created by mvCreateFile, both parts are contained in	one file, with
     the metadata portion usually following the	data portion.  In movie	files
     created on	a Macintosh, the two parts are contained in separate files
     called forks.  Data-forks contain the data	part of	the movie, and
     resource-forks contain the	metadata.  Files containing both parts are
     called single-fork	movie files.

     There are several naming conventions used to associate resource-forks
     with their	data-fork mates.  In one convention, the resource-fork for
     data-fork /tmp/movie.mov (for example) is /tmp/.HSResource/movie.mov:
     i.e. named	identically to the data-fork, residing in a directory called
     .HSResource directly under	the directory containing the data-fork.	 In
     another convention, the resource-fork for the same	data-fork would	be
     /tmp/%movie.mov--both forks in the	same directory,	the resource-fork
     named by prepending a '%' character to the	data-fork name.

     On	a Mac, resource-forks are considered to	be primarily system files, so
     their existence is	transparent to the user.  Therefore, mvOpenFile	always
     expects data-fork names, never resource-fork names.  Given	a data-fork
     filename, it automatically	searches for a resource-fork complying with
     either of the above naming	conventions, and--if found--uses it during the
     opening process.  If no resource-fork is found, it	assumes	the data file
     contains a	single-fork movie.

     Because of	this transparent synthesis of the resource-fork	name from the
     input data-fork name, only	mvOpenFile works with dual-fork	movie files.

     The Movie library provides	the ability to create movies that reference
     data contained in other movie files (see the byReference parameter	of
     mvCopyFramesAtTime(3dm)).	This means that	rather than copying data from
     movie B to	movie A	and creating references	in movie A's metadata to the
     new data, we can merely create references in movie	A's metadata to	the
     data frames residing in movie B.  These references	are called external
     references, or aliases.

     Although this is a	very useful capability,	the resulting movie file
     requires that none	of the files whose data	it uses	be moved, modified, or
     destroyed,	since the files	contain	frames needed by the movie.  To	create
     a movie containing	no external references from one	that does, open	an
     empty movie file, and use mvOptimize(3dm) to copy the external data into
     the new movie's data section.  The	result will be a self-contained, or
     flattened movie.

     Note that flattened vs. nonflattened and single- vs. double-fork movies

									Page 2

mvOpen(3dm)							   mvOpen(3dm)

     are orthogonal concepts.  Single- or dual-fork movie files	may contain
     external references, and therefore	are not	flattened movies, and a	movie
     whose data	is entirely self-contained (i.e. flattened) may	have its data
     and metadata in one or two	files (i.e. single- or dual-forks,

SEE ALSO    [Toc]    [Back]

     mvIntro(3dm), mvCreate(3dm), mvClose(3dm),	mvIsReadOnly(3dm),
     mvGetErrno(3dm), mvCopyFramesAtTime(3dm), mvOptimize(3dm).

									PPPPaaaaggggeeee 3333
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