From: Ronald van Engelen

Completed common sample frequencies for pcm encoded audio in
flac containers using bash script "scripts/create_filemagic_flac"

diff --git a/magic/Magdir/audio b/magic/Magdir/audio
index 0330bbfa80783cd9d4fe5786d1089510137b6bd2..1ea195241a3b37bef475940d3df5ae796603e88b 100644 (file)
--- a/magic/Magdir/audio
+++ b/magic/Magdir/audio
@@ -1,6 +1,6 @@
 
 #------------------------------------------------------------------------------
-# $File: audio,v 1.80 2017/08/13 00:21:47 christos Exp $
+# $File: audio,v 1.81 2017/09/12 15:55:16 christos Exp $
 # audio:  file(1) magic for sound formats (see also "iff")
 #
 # Jan Nicolai Langfeldt (janl@ifi.uio.no), Dan Quinlan (quinlan@yggdrasil.com),
@@ -468,20 +468,25 @@
 >>20   byte&0xe                0xa             \b, 6 channels
 >>20   byte&0xe                0xc             \b, 7 channels
 >>20   byte&0xe                0xe             \b, 8 channels
-# some common sample rates
->>17   belong&0xfffff0         0x2ee000        \b, 192 kHz
->>17   belong&0xfffff0         0x158880        \b, 88.2 kHz
->>17   belong&0xfffff0         0x0ac440        \b, 44.1 kHz
->>17   belong&0xfffff0         0x0bb800        \b, 48 kHz
->>17   belong&0xfffff0         0x07d000        \b, 32 kHz
->>17   belong&0xfffff0         0x056220        \b, 22.05 kHz
->>17   belong&0xfffff0         0x05dc00        \b, 24 kHz
->>17   belong&0xfffff0         0x03e800        \b, 16 kHz
->>17   belong&0xfffff0         0x02b110        \b, 11.025 kHz
->>17   belong&0xfffff0         0x02ee00        \b, 12 kHz
->>17   belong&0xfffff0         0x01f400        \b, 8 kHz
->>17   belong&0xfffff0         0x177000        \b, 96 kHz
->>17   belong&0xfffff0         0x0fa000        \b, 64 kHz
+# sample rates derived from known oscillator frequencies;
+# 24.576 MHz (video/fs=48kHz), 22.5792 (audio/fs=44.1kHz) and
+# 16.384 (other/fs=32kHz).
+>>17   belong&0xfffff0         0x02b110        \b, 11.025 kHz
+>>17   belong&0xfffff0         0x03e800        \b, 16 kHz
++>>17  belong&0xfffff0         0x056220        \b, 22.05 kHz
+>>17   belong&0xfffff0         0x05dc00        \b, 24 kHz
+>>17   belong&0xfffff0         0x07d000        \b, 32 kHz
+>>17   belong&0xfffff0         0x0ac440        \b, 44.1 kHz
+>>17   belong&0xfffff0         0x0bb800        \b, 48 kHz
+>>17   belong&0xfffff0         0x0fa000        \b, 64 kHz
+>>17   belong&0xfffff0         0x158880        \b, 88.2 kHz
+>>17   belong&0xfffff0         0x177000        \b, 96 kHz
+>>17   belong&0xfffff0         0x1f4000        \b, 128 kHz
+>>17   belong&0xfffff0         0x2b1100        \b, 176.4 kHz
+>>17   belong&0xfffff0         0x2ee000        \b, 192 kHz
+>>17   belong&0xfffff0         0x3e8000        \b, 256 kHz
+>>17   belong&0xfffff0         0x562200        \b, 352.8 kHz
+>>17   belong&0xfffff0         0x5dc000        \b, 384 kHz
 >>21   byte&0xf                >0              \b, >4G samples
 >>21   byte&0xf                0               \b
 >>>22  belong                  >0              \b, %u samples

diff --git a/magic/scripts/create_filemagic_flac b/magic/scripts/create_filemagic_flac
new file mode 100755 (executable)
index 0000000..2730303
--- /dev/null
+++ b/magic/scripts/create_filemagic_flac
@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+
+## bash script to generate file magic support for flac.
+## https://github.com/file/file/blob/master/magic/Magdir/audio
+## below "#some common sample rates" (line 471), ie:
+## >>17        belong&0xfffff0         0x2ee000        \b, 192 kHz
+
+LANG=C
+
+target=magic/Magdir/audio
+
+## construct static list of sample rates based on standard crystal
+## oscillator frequencies.
+## 16.384  MHz Unknown audio application
+##             (16384 kHz  = 32 kHz * 512 = 32 * 2^9)
+## 22.5792 MHz Redbook/CD
+##             (22579.2 kHz = 44.1kHz * 512 = 44.1 * 2^9)
+##             also used: 11.2896, 16.9344, 33.8688 and 45.1584
+## 24.576  MHz DAT/Video
+##             (24576 kHz = 48 kHz * 512 = 48 * 2^9)
+##             also used: 49.1520
+
+## 33.8688 > 16.9344
+## 36.864  > 18.432000
+declare -a a_ground_fs=(16384000 22579200 24576000)
+
+## multiply ground clock frequencies by 1953 to get usable base
+## frequencies, for instance:
+##  DAT/video:  24.576  MHz * 1000000 / 512 = 48000Hz
+##  Redbook/CD: 22.5792 MHz * 1000000 / 512 = 44100Hz
+## use base rates for calculating derived rates
+declare -a samplerates
+## min divider: fs/n
+def_fs_n=512
+min_fs_n=4
+## start at base_fs/(def_fs*min_fs)
+## add each derived sample rate to the array
+for base_fs in "${a_ground_fs[@]}"; do 
+    min_fs=$( echo "${base_fs} / ( ${def_fs_n} * ${min_fs_n} )" | bc)
+    ## max multiplier: fs*n*min_fs
+    max_fs_n=$(( 8 * min_fs_n ))
+    n=${max_fs_n}
+    while [[ ${n} -ge 1 ]]; do
+       sample_rate=$(( min_fs * n ))
+       samplerates+=(${sample_rate})
+       n=$(( n / 2 ))
+    done
+done
+
+declare -a stripped_rates
+declare -a lines
+for samplerate in "${samplerates[@]}"; do
+    ## use bc with sed to convert and format Hz to kHz
+    stripped_rate="$(LANG=C bc <<< "scale=5; ${samplerate} / 1000" | \
+                             sed 's#[0\.]*$##g')"
+    ## only add uniq sample rates (should be neccessary
+    if [[ ! "${stripped_rates[@]}" =~ ${stripped_rate} ]]; then
+       printf -v line ">>17\tbelong&%#-15x\t%#08x\t%s, %s kHz\n" \
+              "16777200" \
+              "$(( samplerate * 16 ))" \
+              "\b" \
+              "${stripped_rate}"
+       stripped_rates+=("${stripped_rate}")
+       lines+=("${line}")
+    fi
+
+done
+printf "## start cutting >>> \n"
+## print out the formatted lines
+printf "%s" "${lines[@]}" | sort -k5 -n
+printf "## <<< stop cutting\n"