666af905f3
The packet layout is buf(8), pts(8), dts(8), data(8), size(4), stream_index(4). We had buf, data, size, stream_index — reading the pts timestamp as the data pointer, so every packet was garbage. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
115 lines
3.9 KiB
Nim
115 lines
3.9 KiB
Nim
## Audio capture via libavdevice/libavformat (dlopen at runtime).
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import osproc, strutils
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import scope
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# ── libav C helper bindings ──────────────────────────────────────────
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{.compile: "avhelper.c".}
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{.passL: "-ldl".}
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type
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AVFormatContext = object
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AVPacket = object
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proc av_helper_init(): cint {.importc, cdecl.}
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proc av_helper_open_pulse(ctx: ptr ptr AVFormatContext,
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device: cstring): cint {.importc, cdecl.}
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proc av_helper_find_stream_info(ctx: ptr AVFormatContext): cint
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{.importc, cdecl.}
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proc av_helper_find_audio_stream(ctx: ptr AVFormatContext): cint
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{.importc, cdecl.}
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proc av_helper_read_frame(ctx: ptr AVFormatContext,
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pkt: ptr AVPacket): cint {.importc, cdecl.}
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proc av_helper_packet_stream(pkt: ptr AVPacket): cint {.importc, cdecl.}
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proc av_helper_packet_data(pkt: ptr AVPacket): ptr UncheckedArray[uint8]
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{.importc, cdecl.}
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proc av_helper_packet_size(pkt: ptr AVPacket): cint {.importc, cdecl.}
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proc av_helper_packet_alloc(): ptr AVPacket {.importc, cdecl.}
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proc av_helper_packet_unref(pkt: ptr AVPacket) {.importc, cdecl.}
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proc av_helper_packet_free(pkt: ptr ptr AVPacket) {.importc, cdecl.}
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proc av_helper_close(ctx: ptr ptr AVFormatContext) {.importc, cdecl.}
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# ── Monitor source detection ─────────────────────────────────────────
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proc findMonitorSource(): string =
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try:
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let inspect = execProcess("wpctl",
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args = ["inspect", "@DEFAULT_AUDIO_SINK@"],
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options = {poUsePath, poStdErrToStdOut})
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for line in inspect.splitLines():
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if "node.name" in line:
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let eq = line.find("=")
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if eq >= 0:
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return line[eq+1..^1].strip().strip(chars = {'"', ' '}) & ".monitor"
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except: discard
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""
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# ── Audio capture ────────────────────────────────────────────────────
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type
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AudioCapture* = object
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fmtCtx: ptr AVFormatContext
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packet: ptr AVPacket
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streamIdx: cint
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live*: bool
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proc startAudio*(): AudioCapture =
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let monitor = findMonitorSource()
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if monitor.len == 0: return
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if av_helper_init() < 0: return
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var ctx: ptr AVFormatContext = nil
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if av_helper_open_pulse(addr ctx, monitor.cstring) < 0: return
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if av_helper_find_stream_info(ctx) < 0:
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av_helper_close(addr ctx)
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return
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let idx = av_helper_find_audio_stream(ctx)
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let pkt = av_helper_packet_alloc()
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if pkt == nil:
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av_helper_close(addr ctx)
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return
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AudioCapture(fmtCtx: ctx, packet: pkt, streamIdx: idx.cint, live: true)
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proc stop*(cap: var AudioCapture) =
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if cap.live:
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if cap.packet != nil: av_helper_packet_free(addr cap.packet)
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if cap.fmtCtx != nil: av_helper_close(addr cap.fmtCtx)
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proc sourceLabel*(cap: AudioCapture): string =
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if cap.live: "LIVE" else: "NO SIGNAL"
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proc readSamples*(cap: var AudioCapture, scope: var Scope) =
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if not cap.live: return
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const frameSize = 4 # 2ch × 16-bit
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# Read one packet — av_read_frame blocks until data arrives,
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# which naturally rate-limits the render loop to the audio rate
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let ret = av_helper_read_frame(cap.fmtCtx, cap.packet)
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if ret < 0:
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scope.sampleCount = 0
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return
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if av_helper_packet_stream(cap.packet) != cap.streamIdx:
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av_helper_packet_unref(cap.packet)
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scope.sampleCount = 0
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return
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let data = av_helper_packet_data(cap.packet)
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let size = av_helper_packet_size(cap.packet)
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let frames = min(size div frameSize, scope.samplesL.len)
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for i in 0..<frames:
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let off = i * frameSize
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let left = cast[int16]((data[off + 1].uint16 shl 8) or data[off].uint16)
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let right = cast[int16]((data[off + 3].uint16 shl 8) or data[off + 2].uint16)
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scope.samplesL[i] = left.float / 32768.0
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scope.samplesR[i] = right.float / 32768.0
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scope.sampleCount = frames
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av_helper_packet_unref(cap.packet)
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