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https://github.com/RGBCube/serenity
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ac6c06e235
The `Loader` uses a `Vector<Sample>` to store any samples that the actual audio decoder returned that the loader client did not request yet. However, it did not take that buffer into account when those clients asked for the number of samples loaded. The buffer is an internal implementation detail, and should not be reflected on the external API. This allows LibWeb to keep better track of audio position without any desync caused by the buffer. When using the Serenity `PlaybackStream` implementation as the back end for an `HTMLAudioElement`, this allows us to perfectly stop on the exact last sample of the audio file, so it will not stop before the media element can see that it has finished playback. Note that `Loader::get_more_samples()` also calls `loaded_samples()` to determine how many samples are remaining to load into the output buffer. However, this change appears to be correct even there, given that the samples copied from the internal sample buffer are included in that count.
127 lines
5.1 KiB
C++
127 lines
5.1 KiB
C++
/*
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* Copyright (c) 2018-2022, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Error.h>
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#include <AK/FixedArray.h>
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#include <AK/NonnullOwnPtr.h>
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#include <AK/NonnullRefPtr.h>
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#include <AK/RefCounted.h>
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#include <AK/RefPtr.h>
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#include <AK/Span.h>
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#include <AK/Stream.h>
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#include <AK/StringView.h>
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#include <AK/Try.h>
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#include <LibAudio/GenericTypes.h>
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#include <LibAudio/LoaderError.h>
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#include <LibAudio/Metadata.h>
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#include <LibAudio/Sample.h>
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#include <LibAudio/SampleFormats.h>
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namespace Audio {
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// Experimentally determined to be a decent buffer size on i686:
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// 4K (the default) is slightly worse, and 64K is much worse.
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// At sufficiently large buffer sizes, the advantage of infrequent read() calls is outweighed by the memmove() overhead.
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// There was no intensive fine-tuning done to determine this value, so improvements may definitely be possible.
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constexpr size_t const loader_buffer_size = 8 * KiB;
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// Two seek points should ideally not be farther apart than this.
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// This variable is a heuristic for seek table-constructing loaders.
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constexpr u64 const maximum_seekpoint_distance_ms = 1000;
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// Seeking should be at least as precise as this.
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// That means: The actual achieved seek position must not be more than this amount of time before the requested seek position.
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constexpr u64 const seek_tolerance_ms = 5000;
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using LoaderSamples = ErrorOr<FixedArray<Sample>, LoaderError>;
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using MaybeLoaderError = ErrorOr<void, LoaderError>;
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class LoaderPlugin {
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public:
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explicit LoaderPlugin(NonnullOwnPtr<SeekableStream> stream);
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virtual ~LoaderPlugin() = default;
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// Load as many audio chunks as necessary to get up to the required samples.
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// A chunk can be anything that is convenient for the plugin to load in one go without requiring to move samples around different buffers.
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// For example: A FLAC, MP3 or QOA frame.
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// The chunks are returned in a vector, so the loader can simply add chunks until the requested sample amount is reached.
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// The sample count MAY be surpassed, but only as little as possible. It CAN be undershot when the end of the stream is reached.
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// If the loader has no chunking limitations (e.g. WAV), it may return a single exact-sized chunk.
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virtual ErrorOr<Vector<FixedArray<Sample>>, LoaderError> load_chunks(size_t samples_to_read_from_input) = 0;
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virtual MaybeLoaderError reset() = 0;
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virtual MaybeLoaderError seek(int const sample_index) = 0;
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// total_samples() and loaded_samples() should be independent
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// of the number of channels.
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//
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// For example, with a three-second-long, stereo, 44.1KHz audio file:
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// num_channels() should return 2
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// sample_rate() should return 44100 (each channel is sampled at this rate)
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// total_samples() should return 132300 (sample_rate * three seconds)
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virtual int loaded_samples() = 0;
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virtual int total_samples() = 0;
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virtual u32 sample_rate() = 0;
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virtual u16 num_channels() = 0;
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// Human-readable name of the file format, of the form <full abbreviation> (.<ending>)
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virtual DeprecatedString format_name() = 0;
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virtual PcmSampleFormat pcm_format() = 0;
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Metadata const& metadata() const { return m_metadata; }
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Vector<PictureData> const& pictures() const { return m_pictures; }
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protected:
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NonnullOwnPtr<SeekableStream> m_stream;
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Vector<PictureData> m_pictures;
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Metadata m_metadata;
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};
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class Loader : public RefCounted<Loader> {
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public:
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static ErrorOr<NonnullRefPtr<Loader>, LoaderError> create(StringView path);
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static ErrorOr<NonnullRefPtr<Loader>, LoaderError> create(ReadonlyBytes buffer);
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// Will only read less samples if we're at the end of the stream.
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LoaderSamples get_more_samples(size_t samples_to_read_from_input = 128 * KiB);
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MaybeLoaderError reset() const
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{
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m_plugin_at_end_of_stream = false;
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return m_plugin->reset();
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}
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MaybeLoaderError seek(int const position) const
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{
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m_buffer.clear_with_capacity();
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m_plugin_at_end_of_stream = false;
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return m_plugin->seek(position);
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}
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int loaded_samples() const { return m_plugin->loaded_samples() - (int)m_buffer.size(); }
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int total_samples() const { return m_plugin->total_samples(); }
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u32 sample_rate() const { return m_plugin->sample_rate(); }
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u16 num_channels() const { return m_plugin->num_channels(); }
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DeprecatedString format_name() const { return m_plugin->format_name(); }
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u16 bits_per_sample() const { return pcm_bits_per_sample(m_plugin->pcm_format()); }
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PcmSampleFormat pcm_format() const { return m_plugin->pcm_format(); }
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Metadata const& metadata() const { return m_plugin->metadata(); }
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Vector<PictureData> const& pictures() const { return m_plugin->pictures(); }
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private:
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static ErrorOr<NonnullOwnPtr<LoaderPlugin>, LoaderError> create_plugin(NonnullOwnPtr<SeekableStream> stream);
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explicit Loader(NonnullOwnPtr<LoaderPlugin>);
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mutable NonnullOwnPtr<LoaderPlugin> m_plugin;
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// The plugin can signal an end of stream by returning no (or only empty) chunks.
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mutable bool m_plugin_at_end_of_stream { false };
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mutable Vector<Sample, loader_buffer_size> m_buffer;
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};
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}
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