Add functions related to ffmpeg, ppm files and timestamps to dedicated modules.

src/tscut/tools/ppm.py

@@ -0,0 +1,83 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright (C) 2026 Frédéric Tronel
+
+
+import logging
+import re
+from math import ceil, log
+from os import write
+from typing import IO
+from io import BytesIO
+
+
+from typeguard import typechecked
+
+@typechecked
+def dump_ppm(pictures: bytes, prefix: str, temporaries: list[IO[bytes]]) -> None:
+    """
+    Dump PPM pictures from a bytes buffer to files.
+
+    This function takes a bytes buffer containing PPM pictures, a prefix for the output file names,
+    and a list of temporary files.
+    It extracts each PPM picture from the buffer, checks its validity, and writes it to a file.
+    The output files are named according to the prefix and a zero-padded three-digit number.
+
+    Args:
+        pictures (bytes): The bytes buffer containing the PPM pictures.
+        prefix (str): The prefix for the output file names.
+        temporaries (list[IO[bytes]]): A list of temporary files that will be used to store 
+        the output files.
+
+    Returns:
+        None
+
+    Raises:
+        None, but logs errors if:
+            - the PPM picture is not valid (e.g. wrong magic number, dimensions, or color encoding)
+            - an I/O error occurs while creating or writing to an output file
+    """
+    logger = logging.getLogger(__name__)
+
+    # "P6\nWIDTH HEIGHT\n255\n"
+    pos = 0
+    picture = 0
+
+    logger.debug('Dumping %d pictures: %s', len(pictures),prefix)
+
+    while pos<len(pictures):
+        filename = f'{prefix}-{picture:03d}.ppm'
+        header = BytesIO(pictures[pos:])
+        magic = header.readline().decode('utf8')
+        dimensions = header.readline().decode('utf8')
+        max_value = int(header.readline().decode('utf8'))
+        if magic == 'P6\n':
+            pattern = re.compile('^(?P<width>[0-9]+) (?P<height>[0-9]+)\n$')
+            m = pattern.match(dimensions)
+            if m is not None:
+                width = int(m['width'])
+                height = int(m['height'])
+            else:
+                logger.error('Impossible to parse dimensions of picture')
+                return
+        else:
+            logger.error('Not a PPM picture')
+            return
+
+        if max_value != 255:
+            logger.error('Not a valid PPM picture. Color are not encoded on byte. Max value: %d',
+                         max_value)
+
+        header_len=2+1+ceil(log(width, 10))+1+ceil(log(height, 10))+1+3+1
+        try:
+            with open(filename, 'wb') as out:
+                temporaries.append(out)
+                outfd = out.fileno()
+                length=header_len+3*width*height
+                nb_bytes = 0
+                while nb_bytes < length:
+                    nb_bytes+=write(outfd, pictures[pos+nb_bytes:pos+length])
+                pos+=length
+                picture+=1
+        except OSError:
+            logger.error('Impossible to create file: %s', filename)