Only the residual tokens array needs to be kept for the transforms to
use after all the tokens have been parsed. The token cache is able to
be kept in the stack only for the duration of the token parsing loop.
Since the enum is used as an index to arrays, it unfortunately can't
be converted to an enum class, but at least we can make sure to use it
with the qualified enum name to make things a bit clearer.
Previously, the variables were named similarly to the names in spec
which aren't very human-readable. This adds some utility functions for
dimensional unit conversions and names the variables in residual()
based on their units.
References to 4x4 blocks were also renamed to call them sub-blocks
instead, since unit conversion functions would not be able to begin
with "4x4_blocks".
Moving these to another header allows Parser.h to include less context
structs/classes that were previously in Context.h.
This change will also allow consolidating some common calculations into
Context.h, since we won't be polluting the VP9 namespace as much. There
are quite a few duplicate calculations for block size, transform size,
number of horizontal and vertical sub-blocks per block, all of which
could be moved to Context.h to allow for code deduplication and more
semantic code where those calculations are needed.
Those previous constants were only set and used to select the first and
second transforms done by the Decoder class. By turning it into a
struct, we can make the code a bit more legible while keeping those
transform modes the same size as before or smaller.
The sub-block transform types set and then used in a very small scope,
so now it is just stored in a variable and passed to the two functions
that need it, Parser::tokens() and Decoder::reconstruct().
Note that some of the previous segmentation feature settings must be
preserved when a frame is decoded that doesn't use segmentation.
This change also allowed a few functions in Decoder to be made static.
The motion vector joints enum is set up so that the first bit indicates
that a vector should have a non-zero value in the column, and the
second bit indicates a non-zero value for the row. Taking advantage of
this makes the code a bit more legible.
Previously, we were using size_t, often coerced from bool or u8, to
index reference pairs. Now, they must either be taken directly from
named fields or indexed using the `ReferenceIndex` enum with options
`primary` and `secondary`. With a more explicit method of indexing
these, the compiler can aid in using reference pairs correctly, and
fuzzers may be able to detect undefined behavior more easily.
Candidate vector selections are only used to calculate the new vectors
for the current block, so we only need to keep those for the duration
of the inter_block_mode_info() call.
Candidate vectors are now stored in BlockMotionVectorCandidates, which
contains the fields necessary to choose the vector to use to sample
from the selected reference frame.
Most functions related to motion vectors were renamed to more verbose
but meaningful names.
The log2 of tile counts in the horizontal and vertical dimensions are
now stored in the FrameContext struct to be kept only as long as they
are needed.
This also renames (most?) of the related quantizer functions and
variables to make more sense. I haven't determined what AC/DC stands
for here, but it may be just an arbitrary naming scheme for the first
and subsequent coefficients used to quantize the residuals for a block.
The color config is reused for most inter predicted frames, so we use a
struct ColorConfig to store the config from intra frames, and put it in
a field in Parser to copy from when an inter frame without color config
is encountered.
There are three mutually exclusive frame-showing states:
- Show no new frame, only store the frame as a reference.
- Show a newly decoded frame.
- Show frame from the reference frame store.
Since they are mutually exclusive, using an enum rather than two bools
makes more sense.
These are used to pass context needed for decoding, with mutability
scoped only to the sections that the function receiving the contexts
needs to modify. This allows lifetimes of data to be more explicit
rather than being stored in fields, as well as preventing tile threads
from modifying outside their allowed bounds.
The field was only used once to track whether residual tokens were
present in the block. Parser::tokens() now returns a bool indicating
whether they were present.
These are now passed as parameters to each function that uses them.
These will later be moved to a struct to further reduce the amount of
parameters that get passed around.
Above and left per-frame block contexts are now also parameters passed
to the functions that use them instead of being retrieved when needed
from a field. This will allow them to be more easily moved to a tile-
specific context later.
There are three fields that we need to store from FrameBlockContext to
keep between frames, which are used to parse for those same fields for
the next frame.
The function serves no purpose now, any debug information we want to
pull from the decoder should be instead accessed by some other yet to
be created interface.
All state that needed to persist between calls to decode_block was
previously stored in plain Vector fields. This moves them into a struct
which sets a more explicit lifetime on that data. It may be possible to
store this data on the stack of a function with the appropriate
lifetime now that it is split into its own struct.
The default intra prediction mode was only used to set the sub-block
modes and the y prediction mode. Instead of storing it in a field, with
the sub modes are stored in an Array, we can just pull the last element
to set the y mode.
When errors are encountered by PlaybackManager, it attempts to switch
states to either Stopped or Corrupted. However, that causes it to set
the last presentation media time to the current playback time while the
last presentation time is unexpectedly negative because the seek never
ended.
Ending the seek before the state changes to Stopped or Corrupted
prevents this situation from happening.
This implements the fastest seeking mode available for tracks with cues
using an array of cue points for each track. It approximates the index
based on the seeking timestamp and then finds the earliest cue point
before the timestamp. The approximation assumes that cues will be on
a regular interval, which I don't believe is always the case, but it
should at least be faster than iterating the whole set of cue points
each time.
Cues are stored per track, but most videos will only have cue points
for the video track(s) that are present. For now, this assumes that it
should only seek based on the cue points for the selected track. To
seek audio in a video file, we should copy the seeked iterator over to
the audio track's iterator after seeking is complete. The iterator will
then skip to the next audio block.
Tracks have a timestamp scale value that should be present which scales
each block's timestamp offset to allow video to be synced with audio.
They should also contain a CodecDelay element and may also contain a
TrackOffset that offsets the block timestamps.
Now that we're able to find the nearest keyframe, we can have a fast
seeking mode that only seeks to keyframes, so that it doesn't have to
also decode inter frames until it reaches the timestamp.
The default is still accurate seeking, so that the entire seeking
implementation can be tested.
This just searches sequentially through each block in a SampleIterator
until it finds a block after the specified seek timestamp. Once it
finds one, it will try to set the input/output iterator to the most
recent keyframe. If the iterator's original position is closer to the
target, however, it leaves it at that original position, allowing
callers to continue decoding from that position until they reach the
target timestamp.
This implements the PlaybackManager portion of seeking, so that it can
seek to any frame in the video by dropping all preceding frames until
it reaches the seek point.
MatroskaDemuxer currently will only seek to the start of the video.
That means that every seek has to drop all the frames until it comes
across the target timestamp.
The PlaybackManager::update_presented_frame function was getting out of
hand and adding seeking was making it illegible. This rewrites it to be
(hopefully) quite a bit more readable, and adds a few comments to help
future readers of the code.
In addition, some helpful debugging prints were added that should help
debug any future issues with the player.
With these changes, the seek bar can be used, but only to seek to the
start of the file. Seeking to anywhere else in the file will cause an
error in the demuxer.
The timestamp label that was previously invisible now has its text set
according to either the playback or seek slider's position.
