Add AC-4 Level-4 ISO base media file format support #1265
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Merge latest code from androidx/media main branch
…ries/media into dlb/ac4-level4/dev
…ries/media into dlb/ac4-level4/dev
| // Using first presentation (default presentation) channel count | ||
| int presentationIndex = 0; | ||
| Ac4Presentation ac4Presentation = | ||
| Objects.requireNonNull(ac4Presentations.get(presentationIndex)); |
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Why are we looping over all presentationIndex above and storing it in a Map when all we require is the ac4Presentation for the index 0?
Is it to verify if the file doesn't have bad data? Even in that case storing it in a Map seems an overkill, when we don't intend to use the map for anything else but index 0.
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@rohitjoins,
This AC4 parser implementation is similar as the one in Android Framework: https://cs.android.com/android/platform/superproject/main/+/main:frameworks/av/media/module/extractors/mp4/AC4Parser.cpp;drc=2e87c835abea90b0cf61b42dc9aa8a882f2ef5aa;l=292. It parses all the information for all presentations because there is API https://developer.android.com/reference/android/media/MediaExtractor#getAudioPresentations(int) to fetch the presentations info for appointed audio track.
Since AndroidX Media extractor doesn't support AudioPresentation, I know this loop is redundant now.
But I know Android framework MPEGExtractor was deprecated and it will be replaced by AndroidX Media extractor. Although AndroidX Media doesn't support AudioPresentation now but I believe it will support it sooner or later. That's why I use a Map to store all audio presentation info and keep this logic in my implementation.
If one audio track includes multiple audio presentations, and if application doesn't set which presentation should be played, the Dolby AC-4 decoder will decode the default presentation (the first presentation).
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I would suggest to remove any logic which will be used in the future as it can be added when required. For now we should only parse and use the first presentation.
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@rohitjoins , OK, I'll update the code.
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@rohitjoins, I have updated the code as your suggestion.
This pull request is same as #875. Since 875 is broken due to too many commit numbers, I re-created this new one.
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AC-4 Level-4 (Object Based Audio) is a Dolby official audio stream type for Atmos Music. This code update enables Android Media3 support local MP4 and MPEG-DASH AC-4 Level-4 playback.