80 lines
3.4 KiB
Go
80 lines
3.4 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 "encoding/binary"
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// TrackFragmentDecodeTimeBox Track Fragment Decode Time Box struct
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//
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// 8.8.12 Track fragment decode time
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//
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// Box Type: `tfdt’
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// Container: Track Fragment box (‘traf’)
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// Mandatory: No
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// Quantity: Zero or one
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//
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// The Track Fragment Base Media Decode Time Box provides the absolute decode time, measured on the
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// media timeline, of the first sample in decode order in the track fragment. This can be useful, for
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// example, when performing random access in a file; it is not necessary to sum the sample durations of all
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// preceding samples in previous fragments to find this value (where the sample durations are the deltas
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// in the Decoding Time to Sample Box and the sample_durations in the preceding track runs).
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//
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// The Track Fragment Base Media Decode Time Box, if present, shall be positioned after the Track
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// Fragment Header Box and before the first Track Fragment Run box.
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//
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// If the time expressed in the track fragment decode time (‘tfdt’) box exceeds the sum of the durations of
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// the samples in the preceding movie and movie fragments, then the duration of the last sample
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// preceding this track fragment is extended such that the sum now equals the time given in this box. In
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// this way, it is possible to generate a fragment containing a sample when the time of the next sample is
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// not yet known.
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//
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// In particular, an empty track fragment (with no samples, but with a track fragment decode time box)
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// may be used to establish the duration of the last sample.
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type TrackFragmentDecodeTimeBox struct {
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*FullBox
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// is an integer equal to the sum of the decode durations of all earlier
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// samples in the media, expressed in the media's timescale. It does not include the samples added
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// in the enclosing track fragment.
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BaseMediaDecodeTimeV0 uint32
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// is an integer equal to the sum of the decode durations of all earlier
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// samples in the media, expressed in the media's timescale. It does not include the samples added
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// in the enclosing track fragment.
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BaseMediaDecodeTimeV1 uint64
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}
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const BoxTypeTrackFragmentDecodeTime = "tfdt"
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func init() {
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BoxDefinitions = append(BoxDefinitions, BoxDefinition{
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Type: BoxTypeTrackFragmentDecodeTime,
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ParentTypes: []string{BoxTypeTrackFragment},
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Parser: ParseTrackFragmentDecodeTimeBox,
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})
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}
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// ParseTrackFragmentDecodeTimeBox creates a new track fragment decode time box struct based on bytes
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func ParseTrackFragmentDecodeTimeBox(parser *Parser, filePosition uint64, headerSize uint32, content []byte) (any, error) {
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box := &TrackFragmentDecodeTimeBox{
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FullBox: newFullBox(&Box{filePosition, headerSize}, content[0:4]),
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}
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if box.Version == 0 {
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box.BaseMediaDecodeTimeV0 = binary.BigEndian.Uint32(content[4:8])
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} else {
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box.BaseMediaDecodeTimeV1 = binary.BigEndian.Uint64(content[4:12])
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}
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return box, nil
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}
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