The complexity around not enabling the video renderer before it
has a valid surface is because MediaCodecTrackRenderer supports
a "discard" mode where it pulls through and discards samples
without a decoder. This mode means that if the demo app were to
enable the renderer before supplying the surface, the renderer
could discard the first few frames prior to getting the surface,
meaning video rendering wouldn't happen until the following sync
frame.
To get a handle on complexity, I think we're better off just removing
support for this mode, which nicely decouples how the demo app
handles surfaces v.s. how it handles enabling/disabling renderers.
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
- Remove simple variant. Maintaining both simple + full is
unnecessary effort.
- Remove need to specify content id in Sample definition,
except where it's actually required (for DRM requests in
the Widevine GTS samples)
SampleExtractor will initially only be implemented by FrameworkSampleExtractor
which delegates to a MediaExtractor, but eventually it will also be implemented
by additional extractors.
The sample extractor can be used as a source of samples via DefaultSampleSource.
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
- Move all three buffering constants to a single class (the
chunk source).
- Increase the target buffer to 40s for increased robustness
against temporary network blips.
- Make values configurable via the chunk source constructor.
- Treat captions as a text track for HLS. This allows them to
be enabled/disabled through the demo app UI.
Issue: #165
- Add options to switch abruptly at segment boundaries. Third
parties who guarantee keyframes at the start of segments will
want this, because it makes switching more efficient and hence
rebuffering less likely.
- Switch quality faster when performing a splicing switch (when
we detect that we need to switch variant, we now immediately
request the same segment as we did last time for the new variant,
rather than requesting one more segment for the old variant
before doing this.
