87 lines
3 KiB
Go
87 lines
3 KiB
Go
// Copyright 2024 Martin Riedl
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package gomp4
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import (
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"encoding/binary"
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"fmt"
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)
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// ChunkOffsetBox chunk offset box struct
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//
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// 8.7.5 Chunk Offset Box
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//
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// Box Type: ‘stco’, ‘co64’
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// Container: Sample Table Box (‘stbl’)
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// Mandatory: Yes
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// Quantity: Exactly one variant must be present
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//
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// The chunk offset table gives the index of each chunk into the containing file. There are two variants,
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// permitting the use of 32‐bit or 64‐bit offsets. The latter is useful when managing very large
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// presentations. At most one of these variants will occur in any single instance of a sample table.
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//
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// Offsets are file offsets, not the offset into any box within the file (e.g. Media Data Box). This permits
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// referring to media data in files without any box structure. It does also mean that care must be taken
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// when constructing a self‐contained ISO file with its metadata (Movie Box) at the front, as the size of the
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// Movie Box will affect the chunk offsets to the media data.
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type ChunkOffsetBox struct {
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*FullBox
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// is an integer that gives the number of entries in the following table
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EntryCount uint32
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EntryList []ChunkOffsetEntry
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}
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type ChunkOffsetEntry struct {
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// is a 32 or 64 bit integer that gives the offset of the start of a chunk into its
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// containing media file.
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ChunkOffset uint32
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}
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// BoxTypeChunkOffset Chunk Offset Box
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const BoxTypeChunkOffset = "stco"
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func init() {
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BoxDefinitions = append(BoxDefinitions, BoxDefinition{
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Type: BoxTypeChunkOffset,
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ParentTypes: []string{BoxTypeSampleTable},
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Parser: ParseChunkOffsetBox,
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})
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}
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// ParseChunkOffsetBox creates a new chunk offset box struct based on bytes
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func ParseChunkOffsetBox(parser *Parser, filePosition uint64, headerSize uint32, content []byte) (any, error) {
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box := &ChunkOffsetBox{
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FullBox: newFullBox(&Box{filePosition, headerSize}, content[0:4]),
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}
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// parse entry counter
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box.EntryCount = binary.BigEndian.Uint32(content[4:8])
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// parse offset entries
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position := 8
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for i := 0; i < int(box.EntryCount); i++ {
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newOffsetEntry := ChunkOffsetEntry{
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ChunkOffset: binary.BigEndian.Uint32(content[position+(i*4) : position+4+(i*4)]),
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}
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box.EntryList = append(box.EntryList, newOffsetEntry)
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}
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// validate entries amount
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if len(box.EntryList) != int(box.EntryCount) {
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return box, fmt.Errorf("invalid amount of offset entries at %d; got %d but expected %d", filePosition, len(box.EntryList), box.EntryCount)
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}
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return box, nil
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}
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