python: Add python library wrapper

python/tools/decoder.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+#
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import argparse
+import lc3
+import struct
+import sys
+import wave
+
+parser = argparse.ArgumentParser(description='LC3 Decoder')
+
+parser.add_argument(
+    'lc3_file', nargs='?',
+    help='Input bitstream file, default is stdin',
+    type=argparse.FileType('rb'), default=sys.stdin.buffer)
+
+parser.add_argument(
+    'wav_file', nargs='?',
+    help='Output wave file, default is stdout',
+    type=argparse.FileType('wb'), default=sys.stdout.buffer)
+
+parser.add_argument(
+    '--bitdepth',
+    help='Output bitdepth, default is 16 bits',
+    type=int, choices=[16, 24], default=16)
+
+parser.add_argument(
+    '--libpath', help='LC3 Library path')
+
+args = parser.parse_args()
+
+# --- LC3 File input ---
+
+f_lc3 = args.lc3_file
+
+header = struct.unpack('=HHHHHHHI', f_lc3.read(18))
+if header[0] != 0xcc1c:
+    raise ValueError('Invalid bitstream file')
+
+samplerate = header[2] * 100
+nchannels = header[4]
+frame_duration = header[5] / 100
+stream_length = header[7]
+
+# --- Setup output ---
+
+bitdepth = args.bitdepth
+pcm_size = nchannels * (bitdepth // 8)
+
+f_wav = args.wav_file
+wavfile = wave.open(f_wav)
+wavfile.setnchannels(nchannels)
+wavfile.setsampwidth(bitdepth // 8)
+wavfile.setframerate(samplerate)
+wavfile.setnframes(stream_length)
+
+# --- Setup decoder ---
+
+dec = lc3.Decoder(
+    frame_duration, samplerate, nchannels, libpath=args.libpath)
+frame_length = dec.get_frame_samples()
+encoded_length = stream_length + dec.get_delay_samples()
+
+# --- Decoding loop ---
+
+for i in range(0, encoded_length, frame_length):
+
+    lc3_frame_size = struct.unpack('=H', f_lc3.read(2))[0]
+    pcm = dec.decode(f_lc3.read(lc3_frame_size), bitdepth=bitdepth)
+
+    pcm = pcm[max(encoded_length - stream_length - i, 0) * pcm_size:
+              min(encoded_length - i, frame_length) * pcm_size]
+
+    wavfile.writeframesraw(pcm)
+
+# --- Cleanup ---
+
+wavfile.close()
+
+for f in (f_lc3, f_wav):
+    if f is not sys.stdout.buffer:
+        f.close()