95 lines
3.5 KiB
Go
95 lines
3.5 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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// TimeToSampleBox time to sample box struct
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//
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// 8.6.1.2 Decoding Time to Sample Box
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//
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// Box Type: ‘stts’
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// Container: Sample Table Box (‘stbl’)
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// Mandatory: Yes
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// Quantity: Exactly one
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//
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// This box contains a compact version of a table that allows indexing from decoding time to sample
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// number. Other tables give sample sizes and pointers, from the sample number. Each entry in the table
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// gives the number of consecutive samples with the same time delta, and the delta of those samples. By
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// adding the deltas a complete time‐to‐sample map may be built.
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//
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// The Decoding Time to Sample Box contains decode time delta's: DT(n+1) = DT(n) + STTS(n) where
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// STTS(n) is the (uncompressed) table entry for sample n.
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//
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// The sample entries are ordered by decoding time stamps; therefore the deltas are all non‐negative.
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//
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// The DT axis has a zero origin; DT(i) = SUM(for j=0 to i‐1 of delta(j)), and the sum of all deltas gives the
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// length of the media in the track (not mapped to the overall timescale, and not considering any edit list).
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//
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// The Edit List Box provides the initial CT value if it is non‐empty (non‐zero).
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type TimeToSampleBox 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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Entries []TimeToSampleBoxEntry
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}
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type TimeToSampleBoxEntry struct {
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// s an integer that counts the number of consecutive samples that have the given duration.
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SampleCount uint32
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// is an integer that gives the delta of these samples in the time‐scale of the media.
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SampleDelta uint32
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}
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// BoxTypeDecodingTimeToSample Decoding Time To Sample Box
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const BoxTypeDecodingTimeToSample = "stts"
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func init() {
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BoxDefinitions = append(BoxDefinitions, BoxDefinition{
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Type: BoxTypeDecodingTimeToSample,
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ParentTypes: []string{BoxTypeSampleTable},
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Parser: ParseDecodingTimeToSampleBox,
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})
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}
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// ParseDecodingTimeToSampleBox creates a new decoding time to sample box struct based on bytes
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func ParseDecodingTimeToSampleBox(parser *Parser, filePosition uint64, headerSize uint32, content []byte) (any, error) {
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box := &TimeToSampleBox{
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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 sample entries
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position := 8
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for i := 0; i < int(box.EntryCount); i++ {
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newSampleEntry := TimeToSampleBoxEntry{
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SampleCount: binary.BigEndian.Uint32(content[position+(i*8) : position+4+(i*8)]),
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SampleDelta: binary.BigEndian.Uint32(content[position+4+(i*8) : position+8+(i*8)]),
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}
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box.Entries = append(box.Entries, newSampleEntry)
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}
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// validate entries amount
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if len(box.Entries) != int(box.EntryCount) {
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return box, fmt.Errorf("invalid amount of sample entries at %d; got %d but expected %d", filePosition, len(box.Entries), box.EntryCount)
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}
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return box, nil
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}
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