FreeCalypso > hg > gsm-codec-lib

annotate doc/PCM-file-formats @ 477:4c9222d95647

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
libtwamr encoder: always emit frame->mode = mode; In the original implementation of amr_encode_frame(), the 'mode' member of the output struct was set to 0xFF if the output frame type is TX_NO_DATA. This design was made to mimic the mode field (16-bit word) being set to 0xFFFF (or -1) in 3GPP test sequence format - but nothing actually depends on this struct member being set in any way, and amr_frame_to_tseq() generates the needed 0xFFFF on its own, based on frame->type being equal to TX_NO_DATA. It is simpler and more efficient to always set frame->mode to the actual encoding mode in amr_encode_frame(), and this new behavior has already been documented in doc/AMR-library-API description in anticipation of the present change.
author Mychaela Falconia <falcon@freecalypso.org>
date Sat, 18 May 2024 22:30:42 +0000
parents a217a6eacbad
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
143
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 What file format should be used for 16-bit PCM sample recordings? The first
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 (in the order of development) group of utilities in the present package that
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
3 need to read and write such files are gsm[e]fr-encode and gsm[e]fr-decode,
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
4 designed to mirror amrnb-enc and amrnb-dec from opencore-amr FOSS package;
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
5 these utilities read and write WAV files and even use WAV reading and writing
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
6 functions copied from opencore-amrnb test code.
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
7
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
8 However, as I (Mother Mychaela) keep developing more tools, my use cases become
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
9 more diverse: in some use cases WAV is most convenient (e.g., when playing or
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
10 recording with SoX tools), but in other use cases a raw sample file without any
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 header is much more convenient. To address this diversity of use cases, a pair
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
12 of conversion utilities have been written:
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
13
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
14 pcm16-raw2wav converts from raw format to WAV
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
15 pcm16-wav2raw converts from WAV to raw format
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
16
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
17 Both utilities take a mandatory command line argument specifying the endian
195911f2211c document PCM format conversion utilities
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
18 order for the raw format - there is no default.
152
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
19
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
20 Going forward, I (Mother Mychaela) prefer big-endian format for raw PCM16 files:
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
21 aside from it being the network byte order on the Internet, 16-bit and 32-bit
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
22 numbers appear "naturally" in hex dumps in BE, but not in LE. Therefore, newly
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
23 developed utilities will read and write PCM16 data in "robe" format - "robe" is
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
24 English pronunciation play on "raw BE", and it is also the ritual garment worn
a217a6eacbad doc/PCM-file-formats: establish "robe" format
Mychaela Falconia <falcon@freecalypso.org>
parents: 143
diff changeset
25 by Themyscira telecom priestesses. :-)