cymseed3

cymseed3 reads and writes MiniSEED 2 and 3 in Python with libmseed (EarthScope), the reference C library of the format, bundled in the package (currently version 3.5.4).

• Reading of files, bytes and other buffers (e.g. SeedLink packets), without copies and in linear time; records joined into contiguous segments, or one record at a time with all its header fields.
• Writing of int16, int32, float32, float64 and text samples in every MiniSEED encoding (STEIM1, STEIM2, integers, floats, text), each channel with its own encoding.
• Samples as array.array in their native type, times as integer nanoseconds (the full precision of MiniSEED 3).
• No dependency besides the Python standard library; NumPy arrays are accepted and returned without copies.

cymseed3 is part of the ShakeLab ecosystem, where it is the default MiniSEED backend, but it can be used on its own.

Installation

pip install cymseed3

Python 3.10 or later is required. Binary wheels are published for Linux (x86_64 and aarch64, glibc and musl), macOS (Intel and Apple Silicon) and Windows (64-bit), so no compiler is needed there. On other platforms pip builds the package from source, which needs a C compiler (on macOS, the Xcode command line tools: xcode-select --install; on Windows, the Microsoft C++ Build Tools).

From the repository, for development:

git clone https://github.com/shakelab/cymseed3.git
cd cymseed3
pip install -e ".[dev]"
pytest

Usage

Reading segments

from cymseed3 import MiniSeed, ns_to_string

ms = MiniSeed()
ms.read("day.mseed")             # path, bytes, buffer or binary file
for segment in ms.segments():    # sorted by source identifier and time
    print(segment.sid,           # "FDSN:IV_MODE__H_N_Z"
          segment.codes,         # ("IV", "MODE", "", "HNZ")
          ns_to_string(segment.start_ns),
          segment.rate,          # Hz
          len(segment.data))     # array.array('i', 'f' or 'd')

ms.segments("FDSN:IV_MODE__H_N_?")   # shell-style pattern

Invalid records, truncated records and the warnings of libmseed are reported as MiniSeedWarning and the reading goes on.

Reading records

from cymseed3 import iter_records

for record in iter_records("day.mseed"):
    record.offset, record.reclen, record.format_version
    record.sid, record.start_ns, record.end_ns, record.rate
    record.encoding, record.pubversion, record.samplecnt
    record.flags          # MiniSEED 3 flags (bit 2: clock locked, ...)
    record.extra          # extra headers, e.g. {"FDSN": {"Time": ...}}
    record.raw            # bytes of the record
    record.data           # samples, decoded on first access
    record.info()         # printed summary

MiniSEED 2 fields without a direct MiniSEED 3 counterpart (sequence number, data quality, activity, I/O and quality flags, blockettes) are translated by libmseed into the FDSN extra headers. A SeedLink packet is one record: next(iter_records(packet)).

Writing

import numpy as np
from cymseed3 import MiniSeed, ns_from_string

start = ns_from_string("2026-11-02T10:15:30.123456Z")

ms = MiniSeed()
ms.add(("IV", "MODE", "", "HNZ"), start, 100.0,
       np.arange(1000, dtype=np.int32))                 # STEIM2
ms.add(("IV", "MODE", "", "HNE"), start, 100.0,
       np.zeros(1000, dtype=np.float32))                # encoding 4
ms.add(("IV", "MODE", "", "HNN"), start, 100.0,
       [1, 2, 3], encoding=10)                          # STEIM1
ms.write("out.mseed", version=2, reclen=512)            # or bytes

pack_records packs one series into records with chosen record length, encoding, publication version, flags and extra headers.

With NumPy

import numpy as np

data = np.frombuffer(segment.data, dtype=segment.data.typecode)

License

cymseed3 is distributed under the GNU Lesser General Public License, version 3 or later (COPYING.LESSER, with the GNU General Public License in COPYING).

The bundled libmseed (earthscope/libmseed-<version>, unmodified) is Copyright (C) Chad Trabant, EarthScope Data Services, and distributed under the Apache License, Version 2.0 (earthscope/libmseed-<version>/LICENSE); its test files are used by the tests of cymseed3.

Contact

Issues and pull requests on GitHub. Author: Valerio Poggi.