FreeCalypso > hg > gsm-codec-lib
view doc/PCM-file-formats @ 477:4c9222d95647
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 |
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What file format should be used for 16-bit PCM sample recordings? The first (in the order of development) group of utilities in the present package that need to read and write such files are gsm[e]fr-encode and gsm[e]fr-decode, designed to mirror amrnb-enc and amrnb-dec from opencore-amr FOSS package; these utilities read and write WAV files and even use WAV reading and writing functions copied from opencore-amrnb test code. However, as I (Mother Mychaela) keep developing more tools, my use cases become more diverse: in some use cases WAV is most convenient (e.g., when playing or recording with SoX tools), but in other use cases a raw sample file without any header is much more convenient. To address this diversity of use cases, a pair of conversion utilities have been written: pcm16-raw2wav converts from raw format to WAV pcm16-wav2raw converts from WAV to raw format Both utilities take a mandatory command line argument specifying the endian order for the raw format - there is no default. Going forward, I (Mother Mychaela) prefer big-endian format for raw PCM16 files: aside from it being the network byte order on the Internet, 16-bit and 32-bit numbers appear "naturally" in hex dumps in BE, but not in LE. Therefore, newly developed utilities will read and write PCM16 data in "robe" format - "robe" is English pronunciation play on "raw BE", and it is also the ritual garment worn by Themyscira telecom priestesses. :-)