PHP & MySQL Tutorial json - encode and decode

JSON (JavaScript Object Notation) is a lightweight data-interchange format.

1. It is easy for humans to read and write.
2. It is easy for machines to parse and generate.
3. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999.
4. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others.
5. These properties make JSON an ideal data-interchange language.
6. These are universal data structures. Virtually all modern programming languages support them in one form or another.
7. It makes sense that a data format that is interchangeable with programming languages also be based on these structures.

JSON is built on two structures:

1. A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
2. An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.

In JSON, they take on these forms:

1. An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).
2. An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).

Pictures from http://www.json.org/

Here are some code samples:

<?php

/* object */
echo "\n\nCase 1\n";
$string = '{"audio": "01234", "video":"56789"}';
$obj = json_decode($string);
var_dump($obj);
echo $obj->{"audio"};  echo "\n";
echo $obj->{"video"};  echo "\n";

/* array */
/* When the second parameter of json_decode is true, 
returned objects will be converted into associative arrays. */
echo "\n\nCase 2\n";
$stringArr = '{"audio": "01234", "video":"56789"}';
$arr = json_decode($stringArr, true);
var_dump($arr);
echo $arr{"audio"};  echo "\n";
echo $arr{"video"};  echo "\n";
foreach ($arr as $key => $value) {
    echo "Key: $key; Value: $value\n";
}

echo "\n\nCase 3\n";
$stringArr = '{"audio": {"one": 1, "two": 2, "three": 3, "four": 4},
               "video": {"one": 1, "two": 2, "three": 3, "four": 4}}';
var_dump($stringArr);
$arr = json_decode($stringArr, true );
echo $arr{"audio"}["one"];  echo "\n";
echo $arr{"video"}["four"];  echo "\n";

foreach ($arr["audio"] as $key => $value) {
    echo "Key: $key; Value: $value\n";
}
foreach ($arr["video"] as $key => $value) {
    echo "Key: $key; Value: $value\n";
}

echo "\n\nCase 4\n";
$stringArr = '{"audio": {"one": [1,2,3], "two": [11,22,33], "three": [111,222,333]},
               "video": {"A": [1,2,3], "B": [11,22,33], "C": [111,222,333]}}';
var_dump($stringArr);
$arr = json_decode($stringArr, true );
echo $arr{"audio"}["one"][0];  echo "\n";
echo $arr{"video"}["B"][2];  echo "\n";

foreach ($arr["audio"]["one"] as $key => $value) {
    echo "Key: $key; Value: $value\n";
}
foreach ($arr["video"]["B"] as $key => $value) {
    echo "Key: $key; Value: $value\n";
}

$nOne = sizeof($arr['audio']['one']);
for($i = 0; $i < $nOne; $i++) {
    $value = $arr["audio"]["one"][$i];
    echo "$value ";
}

echo "\n";

$nB = sizeof($arr['video']['B']);
for($i = 0; $i < $nB; $i++) {
    $value = $arr["video"]["B"][$i];
    echo "$value  ";
}
?>

Output:

Case 1
object(stdClass)#1 (2) {
  ["audio"]=>
  string(5) "01234"
  ["video"]=>
  string(5) "56789"
}
01234
56789


Case 2
array(2) {
  ["audio"]=>
  string(5) "01234"
  ["video"]=>
  string(5) "56789"
}
01234
56789
Key: audio; Value: 01234
Key: video; Value: 56789


Case 3
string(123) "{"audio": {"one": 1, "two": 2, "three": 3, "four": 4},
               "video": {"one": 1, "two": 2, "three": 3, "four": 4}}"
1
4
Key: one; Value: 1
Key: two; Value: 2
Key: three; Value: 3
Key: four; Value: 4
Key: one; Value: 1
Key: two; Value: 2
Key: three; Value: 3
Key: four; Value: 4

Case 4
string(147) "{"audio": {"one": [1,2,3], "two": [11,22,33], "three": [111,222,333]},
               "video": {"A": [1,2,3], "B": [11,22,33], "C": [111,222,333]}}"
1
33
Key: 0; Value: 1
Key: 1; Value: 2
Key: 2; Value: 3
Key: 0; Value: 11
Key: 1; Value: 22
Key: 2; Value: 33
1 2 3 
11  22  33

If we want to read the data from a file, we can use the file_get_contents() function:

$json = file_get_contents('data.json');
$data = json_decode($json, true );

Here is one of the xml sample files (shown below) from a json file: ismvInfo.json.

<smil xmlns="http://www.w3.org/2001/SMIL20/Language">
        <head>
                <meta name="clientManifestRelativePath" content="bunny.ismc" />
        </head>
        <body>
                <switch>
                        <video src="bunny_400.ismv" systemBitrate="400074">
                             <param name="trackID" value="1" valueType="data" />
                        </video>
                        <video src="bunny_894.ismv" systemBitrate="895227">
                             <param name="trackID" value="1" valueType="data" />
                        </video>
                        <video src="bunny_2000.ismv" systemBitrate="2001598">
                             <param name="trackID" value="1" valueType="data" />
                        </video>
                        <audio src="bunny_2000.ismv" systemBitrate="127984">
                             <param name="trackID" value="2" valueType="data" />
                        </audio>
                </switch>
        </body>
</smil>

The php code sample:

<?php

$json = file_get_contents('./ismvInfo.json');
$data = json_decode($json, true );

var_dump($data);

$nVideoStream = sizeof($data['video']['src']);
$nAudioStream = sizeof($data['audio']['src']);

$base =  $data['baseName'];
$clientManifest = $base . '.ismc';;
$serverManifest = $base . '.ism';;

/* construct server manifest array */
$mPlaylist = array(
          "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n",
          "<smil xmlns=\"http://www.w3.org/2001/SMIL20/Language\">\n",
          "        <head>\n",
          "                <meta name=\"clientManifestRelativePath\" content=\"$clientManifest\" />\n",
          "        </head>\n",
          "        <body>\n",
          "                <switch>\n"
        );

for ($i=0; $i < $nVideoStream; $i++) {
   $src = $data['video']['src'][$i];
   $bitrate = $data['video']['bitrate'][$i];
   $value = $data['video']['TrackIDvalue'][$i];
   $mPlaylist[] = "                        <video src=\"$src\" systemBitrate=\"$bitrate\">\n";
   $mPlaylist[] = "                             <param name=\"trackID\" value=\"$value\" valueType=\"data\" />\n";
   $mPlaylist[] = "                        </video>\n";
}

for ($i=0; $i < $nAudioStream; $i++) {
   $src = $data['audio']['src'][$i];
   $bitrate = $data['audio']['bitrate'][$i];
   $value = $data['audio']['TrackIDvalue'][$i];
   $mPlaylist[] = "                        <audio src=\"$src\" systemBitrate=\"$bitrate\">\n";
   $mPlaylist[] = "                             <param name=\"trackID\" value=\"$value\" valueType=\"data\" />\n";
   $mPlaylist[] = "                        </audio>\n";
}

$mPlaylist[] = "                </switch>\n";
$mPlaylist[] = "        </body>\n";
$mPlaylist[] = "</smil>\n";

/* server manifest */
$file = fopen($serverManifest,'w');
foreach($mPlaylist as $mp) {
   fwrite($file, $mp);
}
fclose($file);

/* construct client manifest array */
$duration = $data['video']['Duration'];
$nChunks = $data['video']['Chunks'];
$qualityLevels = $data['video']['QualityLevels'];
$cPlaylist = array(
          "<?xml version=\"1.0\" encoding=\"utf-8\"?>\n",
          "<SmoothStreamingMedia MajorVersion=\"2\" MinorVersion=\"0\" Duration=\"$duration\">\n",
          "        <StreamIndex Type=\"video\" QualityLevels=\"$qualityLevels\" Chunks=\"$nChunks\" Url=\"QualityLevels({bitrate})/Fragments(video={start time})\">\n"
   );

for ($i=0; $i < $nVideoStream; $i++) {
   $index = $data['video']['index'][$i];
   $bitrate = $data['video']['bitrate'][$i];
   $fourCC = $data['video']['fourCC'][$i];
   $width = $data['video']['width'][$i];
   $height = $data['video']['height'][$i];
   $codecPrivateData = $data['video']['codecPrivateData'][$i];
   $cPlaylist[] = "                <QualityLevel Index=\"$index\" Bitrate=\"$bitrate\" FourCC=\"$fourCC\" MaxWidth=\"$width\" MaxHeight=\"$height\" CodecPrivateData=\"$codecPrivateData\" />\n";
}

for ($i=0; $i < $nChunks; $i++) {
   $fDurations = $data['video']['fragDurations'][$i];
   $cPlaylist[] = "                <c n=\"$i\" d=\"$fDurations\" />\n";
}
$cPlaylist[] = "        </StreamIndex>\n";

$qualityLevels = $data['audio']['QualityLevels'];
$cPlaylist[] = "        <StreamIndex Type=\"audio\" QualityLevels=\"$qualityLevels\" Chunks=\"$nChunks\" Url=\"QualityLevels({bitrate})/Fragments(audio={start time})\">\n";

$nAudioStream = sizeof($data['audio']['src']);
$bitrate = $data['audio']['bitrate'];
for ($i=0; $i < $nAudioStream; $i++) {
   $index = $data['audio']['index'][$i];
   $bitrate = $data['audio']['bitrate'][$i];
   $fourCC = $data['audio']['fourCC'][$i];
   $samplingRate = $data['audio']['samplingRate'][$i];
   $channels = $data['audio']['channels'][$i];
   $bitsPerSample = $data['audio']['bitsPerSample'][$i];
   $packetSize = $data['audio']['packetSize'][$i];
   $audioTag = $data['audio']['audioTag'][$i];
   $codecPrivateData = $data['audio']['codecPrivateData'][$i];
   $cPlaylist[] = "                <QualityLevel Index=\"$index\" Bitrate=\"$bitrate\" FourCC=\"$fourCC\" SamplingRate=\"$samplingRate\" Channels=\"$channels\" BitsPerSample=\"$bitsPerSample\" PacketSize=\"$packetSize\" AudioTag=\"$audioTag\" CodecPrivateData=\"$codecPrivateData\" />\n";
}

for ($i=0; $i < $nChunks; $i++) {
   $fDurations = $data['audio']['fragDurations'][$i];
   $cPlaylist[] = "                <c n=\"$i\" d=\"$fDurations\" />\n";
}

$cPlaylist[] = "        </StreamIndex>\n";
$cPlaylist[] = "</SmoothStreamingMedia>\n";

/* client manifest */
$file = fopen($clientManifest,'w');
foreach($cPlaylist as $cp) {
   fwrite($file, $cp);
}
fclose($file);

?>

Here are the xml output files: bunny.ism and bunny.ismc: