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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// https://github.com/WICG/web-codecs
// A VideoDecoder processes a queue of configure, decode, and flush requests.
// Requests are taken from the queue sequentially but may be processed
// concurrently.
//
// TODO(sandersd): Specify a tune() implementation for changing decoder
// parameters (separate from stream parameters). This is more important for
// encoders.
[
Exposed=(Window,DedicatedWorker),
RuntimeEnabled=WebCodecs,
ActiveScriptWrappable
] interface VideoDecoder {
// |init| includes an |output| callback for emitting VideoFrames and an
// |error| callback for emitting decode errors.
//
// When in an closed state, all methods will fail.
//
// TODO(sandersd): Consider adding a state or last error attribute.
[CallWith=ScriptState, RaisesException, MeasureAs=WebCodecsVideoDecoder] constructor(VideoDecoderInit init);
// The number of pending decode requests. This does not include requests that
// have been sent to the underlying codec.
//
// Applications can minimize underflow by enqueueing decode requests until
// |decodeQueueSize| is greater than a constant.
//
// TODO(sandersd): Consider adding a predicted output count or other
// backpressure mechanism that considers the state of the underlying codec.
// TODO(sandersd): Consider emitting an event when this number decreases.
readonly attribute long decodeQueueSize;
// Which state the decoder is in, indicating which methods can be called.
readonly attribute CodecState state;
// Set the stream configuration for future decode() requests.
//
// The next decode request must be for a keyframe.
//
// TODO(sandersd): Move the keyframe rule into the bytestream registry.
[RaisesException] void configure(VideoDecoderConfig config);
// Request decoding of an input chunk.
//
// You must call configure() before calling decode() for the first time.
[RaisesException] void decode(EncodedVideoChunk chunk);
// Request output from all previous decode requests.
//
// Resolved after all output for earlier decode requests has been emitted.
//
// The next decode request must be for a keyframe.
//
// TODO(sandersd): Consider relaxing the keyframe requirement.
// TODO(sandersd): Indicate whether the flush() completed successfully or due
// to a reset.
[RaisesException] Promise<void> flush();
// Discard all pending decode requests.
//
// The next decode request must be for a keyframe.
//
// Note: It may be possible to call reset() after a flush() promise has been
// resolved but before it is fulfilled. In that case the flush() promise will
// be fulfilled successfully even though reset() was called.
[RaisesException] void reset();
// Immediately shut down the decoder and free its resources. All pending
// decode requests are aborted.
//
// Not recoverable: make a new VideoDecoder if needed.
[RaisesException] void close();
// Call prior to configure() to determine whether config will be supported.
[CallWith=ScriptState, RaisesException]
static Promise<VideoDecoderSupport> isConfigSupported(VideoDecoderConfig config);
};
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