# MediaCenter : Media center

Media Center is a media resource warehouse provided by EdgerOS. App can use this warehouse to save and read shared media resources, such as mobile phone album synchronization.

User can use the following code to import the MediaCenter module.

var MediaCenter = require('mediacenter');

# Support

The following shows MediaCenter module APIs available for each permissions.

# MediaCenter Class

# new MediaCenter()

• Returns: {Object} mediacenter object.

Create a new MediaCenter object.

# MediaCenter.columns

• {Array} Media resource database search columns.

You can use the columns given by this array to perform a combined condition search.

Each member in the array contains the following members:

• name {String} Column name.
• type {String} Column type.

A typical MediaCenter.columns array is as follows:

[
  { name: 'album',  type: 'text' },
  { name: 'ext',    type: 'text' },
  { name: 'acoid',  type: 'text' },
  { name: 'app',    type: 'text' },
  { name: 'digest', type: 'text' },
  { name: 'time',   type: 'integer' },
  { name: 'size',   type: 'integer' }
];

• album Represents the name of the album, and the default is 'default'.
• ext Media file extension, including '.', such as '.jpg'.
• acoid This media file is saved by which user id.
• app Which application saved this media file.
• digest Media file MD5 digest value, hex format string.
• time The time specified when the media file was saved, for example: new Date().getTime().
• size The size of this media file, in bytes.

When querying conditional parameters, you can use the combination logic of these columns, which is equivalent to the WHERE clause of the SQL statement, or you can use ORDER BY for sorting.

# MediaCenter.refresh([callback])

• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.

Repair database mismatches. Due to the possibility of power failure during the transmission process and other data errors, this function can be repaired, but it takes a long time. During the repair process, the Media Center system service will not respond any operation request.

# MediaCenter Object

# mediacenter.total(callback[, condition])

• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • total {Integer} The total number of media resources.
• condition {String} Statistics search criteria. default: unconditional. Detail to see: Condition.

Count the number of media resources that meet the relevant conditions.

# Example

var mediacenter = new MediaCenter();

mediacenter.total(function(error, count) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Total number:', count);
  }
});

// Can have WHERE clause conditions
mediacenter.total(function(error, count) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Number of default album:', count);
  }
}, `album='default'`);

# mediacenter.space(callback)

• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • space {Object} Media resource disk space statistics.

Get media resource disk space statistics. The space object contains the following members:

• image {Integer} Disk space occupied by image files, in Mbytes.
• media {Integer} Disk space occupied by video or audio, in Mbytes.
• other {Integer} Disk space occupied by other types, in Mbytes.

# Example

mediacenter.space(function(error, space) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Image space(MB):', space.image);
  }
});

# mediacenter.albums(callback[, condition])

• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • list {Array} Media albums array.
• condition {String} Statistics search criteria. default: unconditional. Detail to see: Condition.

Get a list of albums in the media center under specified conditions.

# Example

mediacenter.albums(function(error, list) {
  if (Array.isArray(list)) {
    console.log('All albums:', list);
  }
});

# mediacenter.list(callback[, condition[, limit[, offset]]])

• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • list {Array} Media resource description array.
• condition {String} Statistics search criteria. default: unconditional. Detail to see: Condition.
• limit {Integer} Query entry limit. default: unlimit.
• offset {Integer} Query start position. default: 0.

Get a list of media resource descriptions, each member in the list contains the following members:

• id {Integer} Media resource id.
• ext {String} Media resource extension name.
• size {Integer} Original resource size.
• digest {String} Media resource MD5 digest value, hex format string.

# Example

// Get first 50 media resource descriptions.
mediacenter.list(function(error, descs) {
  if (descs) {
    descs.forEach(function(item) {
      console.log(item.id, item.ext, item.size);
    });
  }
}, undefined, 50);

# mediacenter.info(id, callback)

• id {Integer} Media resource id.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • info {Object} Media resource information.

Get the information of the specified media resource. info contains the following members:

• album {String} The name of the album.
• ext {String} Media resource extension name.
• acoid {String} This media file is saved by which user id.
• app {String} Which application saved this media file.
• digest {String} Media resource MD5 digest value, hex format string.
• time {Integer} The time specified when the media file was saved.
• size {Integer} Original resource size.
• position {Object} Geographic information.
• extra {Object} Custom information when media information is saved.

If position exists, the position object contains the following information:

• latitude {Integer} Latitude.
• longitude {Integer} Longitude.

# mediacenter.remove(id[, callback])

• id {Integer} Media resource id.
• callback {Function} Callback function. default: undefined.
  • error {Error} If an error occurs, indicate the cause of the error.

Remove the media resource specified by id.

# Example

// Delete the oldest resource
mediacenter.list(function(error, list) {
  if (list) {
    mediacenter.remove(list[0].id);
  }
}, `ORDER BY time ASC`, 1);

# mediacenter.get(id, thumbnail, callback[, opt])

• id {Integer} Media resource id.
• thumbnail {Boolean} Whether to get the thumbnail.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • stream {ReadStream} Media resource readable stream.
• opt {Object} Get options.
  • offset {Integer} Video offset in bytes. default: 0.
  • length {Integer} Video length in bytes. default: hole video file size.

Get the specified media resource. When a media resource is saved, EdgerOS will automatically generate a thumbnail of this resource (the audio file has no thumbnail). You can specify whether to get only the thumbnail through the thumbnail parameter. Thumbnails are in JPEG format.

# Example

var dest = fs.createWriteStream('./dest.jpg');

// Get the jpg thumbnail
mediacenter.list(function(error, list) {
  if (list) {
    mediacenter.get(list[0].id, true, function(e, r) {
      if (r) {
        r.pipe(dest);
      }
    })
  }
}, `ext='.jpg'`, 1);

# mediacenter.get(id, thumbnail, callback, dest[, opt])

• id {Integer} Media resource id.
• thumbnail {Boolean} Whether to get the thumbnail.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
• dest {String} Target file.
• opt {Object} Get options.
  • offset {Integer} Video offset in bytes. default: 0.
  • length {Integer} Video length in bytes. default: hole video file size.

Obtain the specified media resources and automatically store them in the specified file.

# Example

// Get the random thumbnail
mediacenter.list(function(error, list) {
  if (list) {
    mediacenter.get(list[0].id, false, function(e) {
      if (error) {
        console.error(error.message);
      } else {
        console.log('Resource get ok!');
      }
    }, `./dest${list[0].ext}`);
  }
}, undefined, 1);

# mediacenter.save(chunk[, opt], callback, ext)

• chunk {Buffer} Media resource data.
• opt {Object} Media resource options.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • id {Integer} Media resource id.
• ext {String} Media resource extension name.

Save a chunk into the media center. opt can contain the following information:

• album {String} The name of the album. default: 'default'.
• acoid {String} This media file is saved by which user id. default: ''.
• position {Object} Geographic information. default: undefined.
• extra {Object} Custom information when media information is saved. default: undefined.

# Example

var chunk = fs.readFile('./aaa.jpg');

mediacenter.save(chunk, function(error) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Resource save ok!');
  }
}, '.jpg');

# mediacenter.save(path[, opt], callback)

• path {String} Media resource file path.
• opt {Object} Media resource options.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • id {Integer} Media resource id.

Save a file into the media center.

# Example

mediacenter.save('./aaa.jpg', function(error) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Resource save ok!');
  }
});

# mediacenter.save(readable[, opt], callback, ext, size)

• readable {ReadStream} Media resource readable stream.
• opt {Object} Media resource options.
• callback {Function} Callback function.
  • error {Error} If an error occurs, indicate the cause of the error.
  • id {Integer} Media resource id.
• ext {String} Media resource extension name.
• size {Integer} Media resource size, in bytes.

Save the readable stream as a media center, which is mostly used for large data video resources. The size represents the maximum transfer size, when this value exceeds the EdgerOS limit, an error will be generated.

# Example

// Readable stream can be web request object.
mediacenter.save(rstream, function(error) {
  if (error) {
    console.error(error.message);
  } else {
    console.log('Resource save ok!');
  }
}, '.mp4', mp4Size);

# Condition

The select condition expression support:

• Relational operations: >, >=, <, <=, =, ==, !=.
  NOTICE:

  = equal to ==

• Logic operation: AND, OR.
• Range operation: BETWEEN...AND.
• Order operation: ORDER BY... DESC|ASC.

# Example

• Relational.

var condition = 'album = "family"'; // `album` name is 'family'.
var condition = `album = 'family'`; // NOTICE: String support "" and ''.
var condition = 'size > 1024'; // File `size` more then 1KB.

• Logic.

var condition = 'album = "family" OR album = "life"'; // `aibum` name is 'family' or 'life'.
var condition = 'album = "family" AND ext = ".png"'; // `aibum` name is 'family' and extension name is '.png'.

• Range.

var condition = 'size BETWEEN 0 AND 1024'; // Select small file.
var condition = 'album = "family" AND size BETWEEN 0 AND 1024';

• Order.

var condition = 'ORDER BY time ASC'; // Sort ascending.
var condition = 'ORDER BY time'; // Default: sort ascending.
var condition = 'ORDER BY time DESC'; // Sort descending.

• Combination.

var condition = 'album = "family" ORDER BY time';
var condition = 'album = "family" AND ext = ".png" ORDER BY time DESC';