FreeCalypso > hg > gsm-codec-lib
view doc/Binary-file-format @ 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 | f469bad44c0e |
| children |
line wrap: on
line source
We (Themyscira Wireless) define our own binary file format for testing of GSM 06.10 (FR) and EFR codec functions; this format of ours is an extension of classic .gsm format from libgsm/toast. The original libgsm file format is a directly abutted sequence of 33-byte libgsm frames, equivalent to RTP frames for GSM FR, with the upper nibble of the first byte in each frame equal to 0xD, serving as a signature. We simply extend this idea: our version is still a directly abutted sequence of binary records, but each record is now one of 3 possibilities: - a 33-byte GSM FR frame in libgsm/RTP format, 0xD signature - a 31-byte GSM EFR frame in RTP format (ETSI TS 101 318), 0xC signature - a 2-byte Themyscira-extension BFI marker, 0xBF signature, see below File reading functions begin by reading only one byte; this byte, once decoded, tells us how many more bytes need to be read, and frame synchronization is thus maintained. The recommended filename suffix for extended-libgsm binary files in the present format is .gsmx; of course dot-separated filename suffixes hold absolutely no special meaning on Unix systems, but many developers still strongly prefer to have them for psychological comfort. Any gsmx file (FR or EFR) can be dumped in human-readable form with our gsmrec-dump utility. This utility turns every read frame from bytes into codec parameters with gsmfr_unpack_to_array() or EFR_frame2params(), and then displays those parameters in a sensible manner, with a per-frame header line followed by 4 lines of subframe parameters. FR and EFR frames are not expected to be mixed in the same stream recording; our low-level binary file reading function and gsmrec-dump will grok such mixing just fine, but each higher-level test program (beyond gsmrec-dump) is expected to be written for only one codec, either FR or EFR. BFI marker format ================= Every 20 ms frame in our gsmx files is either a good FR/EFR frame or a BFI (Bad Frame Indication) marker. The BFI marker format used in our gsmx file format is the same format which we (Themyscira Wireless) previously used in our GSM RAN RTP transport, before switching to our current TRAUlike RTP format. This BFI marker format is quite simple: byte 0: 0xBF signature; byte 1: least-significant bit encoding TAF per GSM 06.31 or GSM 06.81, section 6.1.1 in both documents; other bits are reserved.