daniel-c-harvey
33d6f34d8a
Background-job transcode (ffmpeg/libopus) after source store; pure C# Ogg walker builds the 0.5s-bucketed granule→byte seek index + captures the OpusHead/OpusTags setup header into a per-track sidecar in a new track-opus vault. Best-effort, additive, regenerated on replace-audio.
58 lines
2.4 KiB
C#
58 lines
2.4 KiB
C#
using System.Buffers.Binary;
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namespace DeepDrftContent.Processors.Opus;
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/// <summary>
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/// The single derived sidecar artifact per track (§3.4a B, recommended design): the Opus setup header
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/// (<c>OpusHead</c> + <c>OpusTags</c>) followed by the granule→byte seek index. The client fetches this
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/// once on track load and parses it into its <c>OpusSeekData</c>, so it always has both the setup bytes
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/// (to prepend to any mid-stream slice) and the accurate seek transfer function before it ever issues a
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/// Range fetch — including a window that opens away from byte 0 (UC9).
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/// </summary>
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/// <param name="SetupHeaderBytes">The verbatim OpusHead + OpusTags pages.</param>
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/// <param name="SeekIndex">The bucketed granule→byte seek index.</param>
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public sealed record OpusSidecar(byte[] SetupHeaderBytes, OggOpusSeekIndex SeekIndex)
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{
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/// <summary>
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/// Serializes to <c>[uint32 setupHeaderLength][setup-header bytes][seek-index blob]</c>. The
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/// length prefix lets the client split the two regions with one read; the seek-index blob carries
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/// its own self-describing header (<see cref="OggOpusSeekIndex.ToBytes"/>), so it needs no trailing
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/// length.
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/// </summary>
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public byte[] ToBytes()
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{
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var indexBytes = SeekIndex.ToBytes();
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var bytes = new byte[4 + SetupHeaderBytes.Length + indexBytes.Length];
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var span = bytes.AsSpan();
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BinaryPrimitives.WriteUInt32LittleEndian(span[..4], (uint)SetupHeaderBytes.Length);
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SetupHeaderBytes.CopyTo(span.Slice(4));
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indexBytes.CopyTo(span.Slice(4 + SetupHeaderBytes.Length));
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return bytes;
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}
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/// <summary>
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/// Parses a blob produced by <see cref="ToBytes"/>. Returns null on any structural inconsistency
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/// (short blob, length prefix that overruns, or an unparseable index) — the format is exact, so a
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/// malformed blob is corruption.
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/// </summary>
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public static OpusSidecar? FromBytes(ReadOnlySpan<byte> bytes)
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{
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if (bytes.Length < 4)
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return null;
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var setupLength = BinaryPrimitives.ReadUInt32LittleEndian(bytes[..4]);
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var indexStart = 4 + (long)setupLength;
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if (bytes.Length < indexStart)
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return null;
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var setupHeader = bytes.Slice(4, (int)setupLength).ToArray();
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var index = OggOpusSeekIndex.FromBytes(bytes.Slice((int)indexStart));
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if (index is null)
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return null;
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return new OpusSidecar(setupHeader, index);
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}
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}
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