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75 lines
1.6 KiB
75 lines
1.6 KiB
4 years ago
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# Media Source Extensions Notes
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A collection of findings experimenting with Media Source Extensions on
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Chrome 36.
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* Specifying an audio and video codec when creating a source buffer
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but passing in an initialization segment with only a video track
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results in a decode error
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## ISO Base Media File Format (BMFF)
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### Init Segment
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A working initialization segment is outlined below. It may be possible
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to trim this structure down further.
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- `ftyp`
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- `moov`
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- `mvhd`
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- `trak`
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- `tkhd`
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- `mdia`
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- `mdhd`
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- `hdlr`
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- `minf`
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- `mvex`
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### Media Segment
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The structure of a minimal media segment that actually encapsulates
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movie data is outlined below:
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- `moof`
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- `mfhd`
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- `traf`
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- `tfhd`
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- `tfdt`
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- `trun` containing samples
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- `mdat`
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### Structure
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sample: time {number}, data {array}
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chunk: samples {array}
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track: samples {array}
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segment: moov {box}, mdats {array} | moof {box}, mdats {array}, data {array}
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track
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chunk
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sample
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movie fragment -> track fragment -> [samples]
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### Sample Data Offsets
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Movie-fragment Relative Addressing: all trun data offsets are relative
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to the containing moof (?).
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Without default-base-is-moof, the base data offset for each trun in
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trafs after the first is the *end* of the previous traf.
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#### iso5/DASH Style
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moof
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|- traf (default-base-is-moof)
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| |- trun_0 <size of moof> + 0
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| `- trun_1 <size of moof> + 100
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`- traf (default-base-is-moof)
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`- trun_2 <size of moof> + 300
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mdat
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|- samples_for_trun_0 (100 bytes)
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|- samples_for_trun_1 (200 bytes)
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`- samples_for_trun_2
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#### Single Track Style
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moof
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`- traf
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`- trun_0 <size of moof> + 0
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mdat
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`- samples_for_trun_0
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