Support is provided for the following schemes:
urn:mpeg:dash:utc:direct:2012
urn:mpeg:dash:utc:http-iso:2014
urn:mpeg:dash:utc:http-xsdate:2012
urn:mpeg:dash:utc:http-xsdate:2014
1. AdtsReader would previously copy all data through an intermediate
adtsBuffer. This change eliminates the additional copy step, and
instead copies directly into Sample objects.
2. PesReader would previously accumulate a whole packet by copying
multiple TS packets into an intermediate buffer. This change
eliminates this copy step. After the change, TS packet buffers
are propagated directly to PesPayloadReaders, which are required
to handle partial payload data correctly. The copy steps in the
extractor are simplified from:
DataSource->Ts_BitArray->Pes_BitArray->Sample->SampleHolder
To:
DataSource->Ts_BitArray->Sample->SampleHolder
Issue: #278
- TsExtractor is now based on ParsableByteArray rather than BitArray.
This makes is much clearer that, for the most part, data is byte
aligned. It will allow us to optimize TsExtractor without worrying
about arbitrary bit offsets.
- BitArray is renamed ParsableBitArray for consistency, and is now
exclusively for bit-stream level reading.
- There are some temporary methods in ParsableByteArray that should be
cleared up once the optimizations are in place.
Issue: #278
This is the start of a sequence of changes to fix the ref'd
github issue. Currently TsExtractor involves multiple memory
copy steps:
DataSource->Ts_BitArray->Pes_BitArray->Sample->SampleHolder
This is inefficient, but more importantly, the copy into
Sample is problematic, because Samples are of dynamically
varying size. The way we end up expanding Sample objects to
be large enough to hold the data being written means that we
end up gradually expanding all Sample objects in the pool
(which wastes memory), and that we generate a lot of GC churn,
particularly when switching to a higher quality which can
trigger all Sample objects to expand.
The fix will be to reduce the copy steps to:
DataSource->TsPacket->SampleHolder
We will track Pes and Sample data with lists of pointers into
TsPackets, rather than actually copying the data. We will
recycle these pointers.
The following steps are approximately how the refactor will
progress:
1. Start reducing use of BitArray. It's going to be way too
complicated to track bit-granularity offsets into multiple packets,
and allow reading across packet boundaries. In practice reads
from Ts packets are all byte aligned except for small sections,
so we'll move over to using ParsableByteArray instead, so we
only need to track byte offsets.
2. Move TsExtractor to use ParsableByteArray except for small
sections where we really need bit-granularity offsets.
3. Do the actual optimization.
Issue: #278
Without this, the byte is cast as follows (in bits) if the top
byte is set:
10000010 -> 1000000000000000000000000000010
This works because we then always shift at least one bit left,
and only look at the bottom 8 bits of the result. It's confusing
though. It's clearer if the cast to int gives just adds zeros to
the front, like:
10000010 -> 0000000000000000000000010000010
Note: This adds support for the majority of DASH live streams,
however we do not yet correctly support live streams that rely
on UtcTimingElements in their manifests.
Issue: #52
The timestamp scaling in SegmentBase.getSegmentTimeUs was
overflowing for some streams. Apply a similar trick to that
applied in the SmoothStreaming case to fix it.
This allows ManifestFetcher to both execute the initial
manifest load and be plugged into an ExoPlayer ChunkSource,
where it can be used for repeated manfiest refreshes during
live playback.
2. Common interface for manifest parsers.
- This effectively moves the common interface from the Fetcher level
(i.e. ManifestFetcher) to the Parser level (i.e. ManifestParser).
- The motivation here is to allow the implementation of components that
can work with a generic ManifestParser implementation.
Since we have a Format class as well, it's very confusing that
FormatHolder actually holds a MediaFormat. I think it's quite
likely that Format will need promoting into the root package as
part of the HLS work, which will make this even more confusing
(although it is possible that for HLS we'll define yet another
Format class, if it turns out we need significantly different
fields).
Note - I deliberately avoided renaming the formatHolder
args/params, because they're not particularly ambiguous and
because it introduces some ugly line breaks.
- Allow the content type of an adaptation set to be inferred
from the mimeTypes of the contained representations.
- Ensure the contained mimeTypes are consistent with one
another, and with the adaptation set.
Ref: Issue #2
