getid3_amr Class Reference

getID3() by James Heinrich info@.nosp@m.geti.nosp@m.d3.or.nosp@m.g // More...

Inheritance diagram for getid3_amr:

Collaboration diagram for getid3_amr:

Public Member Functions
	Analyze ()
	amr_mode_bitrate ($key)
	amr_mode_bytes_per_frame ($key)
Public Member Functions inherited from getid3_handler
	__construct (getID3 $getid3, $call_module=null)
	Analyze ()
	AnalyzeString ($string)
	setStringMode ($string)
	saveAttachment ($name, $offset, $length, $image_mime=null)

Additional Inherited Members
Protected Member Functions inherited from getid3_handler
	ftell ()
	fread ($bytes)
	fseek ($bytes, $whence=SEEK_SET)
	feof ()
	isDependencyFor ($module)
	error ($text)
	warning ($text)
	notice ($text)
Protected Attributes inherited from getid3_handler
	$getid3
	$data_string_flag = false
	$data_string = ''
	$data_string_position = 0
	$data_string_length = 0

Detailed Description

getID3() by James Heinrich info@.nosp@m.geti.nosp@m.d3.or.nosp@m.g //

Definition at line 18 of file module.audio.amr.php.

Member Function Documentation

amr_mode_bitrate()

getid3_amr::amr_mode_bitrate

(

$key

)

Definition at line 67 of file module.audio.amr.php.

                                               {
                static $amr_mode_bitrate = array(
                        0 =>  4750,
                        1 =>  5150,
                        2 =>  5900,
                        3 =>  6700,
                        4 =>  7400,
                        5 =>  7950,
                        6 => 10200,
                        7 => 12200,
                );
                return (isset($amr_mode_bitrate[$key]) ? $amr_mode_bitrate[$key] : false);
        }

References $key.

amr_mode_bytes_per_frame()

getid3_amr::amr_mode_bytes_per_frame

(

$key

)

Definition at line 81 of file module.audio.amr.php.

                                                       {
                static $amr_mode_bitrate = array(
                        0 =>  13, // 1-byte frame header +  95 bits [padded to: 12 bytes] audio data
                        1 =>  14, // 1-byte frame header + 103 bits [padded to: 13 bytes] audio data
                        2 =>  16, // 1-byte frame header + 118 bits [padded to: 15 bytes] audio data
                        3 =>  18, // 1-byte frame header + 134 bits [padded to: 17 bytes] audio data
                        4 =>  20, // 1-byte frame header + 148 bits [padded to: 19 bytes] audio data
                        5 =>  21, // 1-byte frame header + 159 bits [padded to: 20 bytes] audio data
                        6 =>  27, // 1-byte frame header + 204 bits [padded to: 26 bytes] audio data
                        7 =>  32, // 1-byte frame header + 244 bits [padded to: 31 bytes] audio data
                );
                return (isset($amr_mode_bitrate[$key]) ? $amr_mode_bitrate[$key] : false);
        }

References $key.

Referenced by Analyze().

Here is the caller graph for this function:

Analyze()

getid3_amr::Analyze

(

)

Reimplemented from getid3_handler.

Definition at line 21 of file module.audio.amr.php.

                                  {
                $info = &$this->getid3->info;
 
                $this->fseek($info['avdataoffset']);
                $AMRheader = $this->fread(6);
 
                $magic = '#!AMR'."\x0A";
                if (substr($AMRheader, 0, 6) != $magic) {
                        $this->error('Expecting "'.getid3_lib::PrintHexBytes($magic).'" at offset '.$info['avdataoffset'].', found "'.getid3_lib::PrintHexBytes(substr($AMRheader, 0, 6)).'"');
                        return false;
                }
 
                // shortcut
                $info['amr'] = array();
                $thisfile_amr = &$info['amr'];
 
                $info['fileformat']               = 'amr';
                $info['audio']['dataformat']      = 'amr';
                $info['audio']['bitrate_mode']    = 'vbr';   // within a small predefined range: 4.75kbps to 12.2kbps
                $info['audio']['bits_per_sample'] =    13;   // http://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec: "Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz"
                $info['audio']['sample_rate']     =  8000;   // http://en.wikipedia.org/wiki/Adaptive_Multi-Rate_audio_codec: "Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz"
                $info['audio']['channels']        =     1;
                $thisfile_amr['frame_mode_count'] = array(0=>0, 1=>0, 2=>0, 3=>0, 4=>0, 5=>0, 6=>0, 7=>0);
 
                $buffer = '';
                do {
                        if ((strlen($buffer) < $this->getid3->fread_buffer_size()) && !feof($this->getid3->fp)) {
                                $buffer .= $this->fread($this->getid3->fread_buffer_size() * 2);
                        }
                        $AMR_frame_header = ord(substr($buffer, 0, 1));
                        $codec_mode_request = ($AMR_frame_header & 0x78) >> 3; // The 2nd bit through 5th bit (counting the most significant bit as the first bit) comprise the CMR (Codec Mode Request), values 0-7 being valid for AMR. The top bit of the CMR can actually be ignored, though it is used when AMR forms RTP payloads. The lower 3-bits of the header are reserved and are not used. Viewing the header from most significant bit to least significant bit, the encoding is XCCCCXXX, where Xs are reserved (typically 0) and the Cs are the CMR.
                        if ($codec_mode_request > 7) {
                                break;
                        }
                        $thisfile_amr['frame_mode_count'][$codec_mode_request]++;
                        $buffer = substr($buffer, $this->amr_mode_bytes_per_frame($codec_mode_request));
                } while (strlen($buffer) > 0);
 
                $info['playtime_seconds'] = array_sum($thisfile_amr['frame_mode_count']) * 0.020; // each frame contain 160 samples and is 20 milliseconds long
                $info['audio']['bitrate'] = (8 * ($info['avdataend'] - $info['avdataoffset'])) / $info['playtime_seconds']; // bitrate could be calculated from average bitrate by distributation of frame types. That would give effective audio bitrate, this gives overall file bitrate which will be a little bit higher since every frame will waste 8 bits for header, plus a few bits for octet padding
                $info['bitrate'] = $info['audio']['bitrate'];
 
                return true;
        }

References $info, amr_mode_bytes_per_frame(), getid3_handler\error(), getid3_handler\feof(), getid3_handler\fread(), getid3_handler\fseek(), and getid3_lib\PrintHexBytes().

Here is the call graph for this function:

---

The documentation for this class was generated from the following file:

• libs/composer/vendor/james-heinrich/getid3/getid3/module.audio.amr.php