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#! /usr/bin/env python
# -*- coding: utf-8 -*-
# Copyright 2016 Google Inc. All rights reserved.
#
# 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.
"""MPEG processing classes.
Tool for loading mpeg4 files and manipulating atoms.
"""
import io
import struct
from spatialmedia.mpeg import constants
def load(fh, position, end):
"""Loads the box located at a position in a mp4 file.
Args:
fh: file handle, input file handle.
position: int or None, current file position.
Returns:
box: box, box from loaded file location or None.
"""
if position is None:
position = fh.tell()
fh.seek(position)
header_size = 8
size = struct.unpack(">I", fh.read(4))[0]
name = fh.read(4)
if size == 1:
size = struct.unpack(">Q", fh.read(8))[0]
header_size = 16
if size < 8:
print("Error, invalid size {} in {} at {}".format(size, name, position))
return None
if (position + size) > end:
print("Error: Leaf box size exceeds bounds.")
return None
new_box = Box()
new_box.name = name
new_box.position = position
new_box.header_size = header_size
new_box.content_size = size - header_size
new_box.contents = None
return new_box
class Box(object):
"""MPEG4 box contents and behaviour true for all boxes."""
def __init__(self):
self.name = ""
self.position = 0
self.header_size = 0
self.content_size = 0
self.contents = None
def content_start(self):
return self.position + self.header_size
def save(self, in_fh, out_fh, delta):
"""Save box contents prioritizing set contents.
Args:
in_fh: file handle, source to read box contents from.
out_fh: file handle, destination for written box contents.
delta: int, index update amount.
"""
if self.header_size == 16:
out_fh.write(struct.pack(">I", 1))
out_fh.write(self.name)
out_fh.write(struct.pack(">Q", self.size()))
elif self.header_size == 8:
out_fh.write(struct.pack(">I", self.size()))
out_fh.write(self.name)
if self.content_start():
in_fh.seek(self.content_start())
if self.name == constants.TAG_STCO:
stco_copy(in_fh, out_fh, self, delta)
elif self.name == constants.TAG_CO64:
co64_copy(in_fh, out_fh, self, delta)
elif self.contents:
out_fh.write(self.contents)
else:
tag_copy(in_fh, out_fh, self.content_size)
def set(self, new_contents):
"""Sets / overwrites the box contents."""
self.contents = new_contents
self.content_size = len(contents)
def size(self):
"""Total size of a box.
Returns:
Int, total size in bytes of the box.
"""
return self.header_size + self.content_size
def print_structure(self, indent=""):
"""Prints the box structure."""
size1 = self.header_size
size2 = self.content_size
print("{0} {1} [{2}, {3}]".format(indent, self.name, size1, size2))
def tag_copy(in_fh, out_fh, size):
"""Copies a block of data from in_fh to out_fh.
Args:
in_fh: file handle, source of uncached file contents.
out_fh: file handle, destination for saved file.
size: int, amount of data to copy.
"""
# On 32-bit systems reading / writing is limited to 2GB chunks.
# To prevent overflow, read/write 64 MB chunks.
block_size = 64 * 1024 * 1024
while (size > block_size):
contents = in_fh.read(block_size)
out_fh.write(contents)
size = size - block_size
contents = in_fh.read(size)
out_fh.write(contents)
def index_copy(in_fh, out_fh, box, mode, mode_length, delta=0):
"""Update and copy index table for stco/co64 files.
Args:
in_fh: file handle, source to read index table from.
out_fh: file handle, destination for index file.
box: box, stco/co64 box to copy.
mode: string, bit packing mode for index entries.
mode_length: int, number of bytes for index entires.
delta: int, offset change for index entries.
"""
fh = in_fh
if not box.contents:
fh.seek(box.content_start())
else:
fh = io.BytesIO(box.contents)
header = struct.unpack(">I", fh.read(4))[0]
values = struct.unpack(">I", fh.read(4))[0]
new_contents = []
new_contents.append(struct.pack(">I", header))
new_contents.append(struct.pack(">I", values))
for i in range(values):
content = fh.read(mode_length)
content = struct.unpack(mode, content)[0] + delta
new_contents.append(struct.pack(mode, content))
out_fh.write(b"".join(new_contents))
def stco_copy(in_fh, out_fh, box, delta=0):
"""Copy for stco box.
Args:
in_fh: file handle, source to read index table from.
out_fh: file handle, destination for index file.
box: box, stco box to copy.
delta: int, offset change for index entries.
"""
index_copy(in_fh, out_fh, box, ">I", 4, delta)
def co64_copy(in_fh, out_fh, box, delta=0):
"""Copy for co64 box.
Args:
in_fh: file handle, source to read index table from.
out_fh: file handle, destination for index file.
box: box, co64 box to copy.
delta: int, offset change for index entries.
"""
index_copy(in_fh, out_fh, box, ">Q", 8, delta) |