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doc/AMR-study-utils: update for the current situation
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 10 May 2024 18:45:36 +0000
parents a053cf0bac04
children b094bc07051a
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1 Standalone command line utilities for FR and EFR codecs
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2 =======================================================
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4 The pre-existing FOSS opencore-amr package includes amrnb-enc and amrnb-dec test
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5 programs: the first reads linear PCM from a WAV file and emits AMR encoder
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6 output in a .amr file (RFC 4867 AMR storage format), the second reads this .amr
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7 format and emits AMR decoder output as WAV. Inspired by these simple test
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8 programs, the present package offers equivalent command line utilities for GSM
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9 FR and EFR codecs. Here they are:
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11 gsmfr-encode This utility reads linear PCM from a WAV file, runs the
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12 bit-exact GSM 06.10 encoder and writes the output in the
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13 classic .gsm format (directly abutted FR codec frames of 33
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14 bytes each). We don't currently have a Tx-side DTX
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15 implementation (VAD etc) for GSM-FR, hence the output from
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16 gsmfr-encode will always consist of good speech frames only.
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18 gsmfr-decode This utility reads our gsmx format (see Binary-file-format
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19 article), which is a superset of the classic libgsm format.
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20 The input to gsmfr-decode may be a pure .gsm recording as
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21 produced by gsmfr-encode or toast from libgsm package, or it
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22 can also contain SID frames and/or BFI markers. The processing
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23 performed by gsmfr-decode begins with our FR1 Rx DTX handler
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24 preprocessor, which will be an identity transform for pure .gsm
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25 input (most of the time) but becomes important for real-world
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26 input containing SIDs and BFIs, and is followed by the bit-exact
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27 GSM 06.10 decoder. The decoded output is written as WAV.
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29 gsmefr-encode This utility reads linear PCM from a WAV file, runs our EFR
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30 encoder (Themyscira libgsmefr) and writes the output in our gsmx
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31 format. There is an option to enable or disable DTX: -d enables
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32 DTX, otherwise it is disabled. (This option mirrors amrnb-enc.)
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33
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34 gsmefr-decode This utility reads our gsmx format (which must be EFR, not FR1)
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35 and feeds all frames and BFIs to our EFR decoder. The decoded
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36 output is written as WAV.
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38 The above are original programs that read WAV input for encoding and write WAV
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39 output from decoding. We now also have raw versions that read and write our
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40 "robe" (raw big-endian) format instead:
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42 gsmfr-encode-r Just like gsm[e]fr-encode, but reading "robe" instead of WAV.
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43 gsmefr-encode-r
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45 gsmfr-decode-r Just like gsm[e]fr-decode, but writing "robe" instead of WAV.
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46 gsmefr-decode-r
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48 Please see PCM-file-formats article for the rationale.
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50 Additions for libgsmfr2
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51 =======================
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53 With the introduction of libgsmfr2, gsmfr-* codec utilities have undergone some
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54 changes:
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56 * gsmfr-decode and gsmfr-decode-r now implement the optional decoder homing
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57 feature, detecting and acting upon GSM 06.10 decoder homing frames.
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59 * gsmfr-encode-r takes an optional -h flag that enables the encoder homing
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60 function; it is disabled by default. The same feature was not replicated in
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61 WAV-reading gsmfr-encode, as WAV format is poorly suited for tinkering-
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62 oriented bit-exact work.
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64 * There is a new utility named gsmfr-decode-rb, where rb stands for "raw basic".
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65 This utility emits "robe" output like gsmfr-decode-r, but it performs only
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66 "basic" GSM 06.10 decoding, without the Rx DTX preprocessor step. BFI frame
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67 gaps in input are not allowed, and there is no SID detection.