mirror of
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snap next steps egress review
This commit is contained in:
Anton Afanasyeu
383
docs/_pdf_build/build_egress_review_pdf.py
Normal file
383
docs/_pdf_build/build_egress_review_pdf.py
Normal file
@@ -0,0 +1,383 @@
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#!/usr/bin/env python3
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"""Build 20260521_next_gen_steps_egress_review.pdf from summary text and diagram PNGs."""
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from __future__ import annotations
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import subprocess
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import sys
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from pathlib import Path
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from reportlab.lib import colors
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from reportlab.lib.enums import TA_LEFT
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from reportlab.lib.pagesizes import A4
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from reportlab.lib.styles import ParagraphStyle, getSampleStyleSheet
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from reportlab.lib.units import cm
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from reportlab.platypus import (
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Image,
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PageBreak,
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Paragraph,
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SimpleDocTemplate,
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Spacer,
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Table,
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TableStyle,
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)
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ROOT = Path(__file__).resolve().parents[2]
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BUILD = Path(__file__).resolve().parent
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OUT_PDF = ROOT / "20260521_next_gen_steps_egress_review.pdf"
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MM = [
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("diagram_current_arch.mmd", "diagram_current_arch.png", "Current sender path (1 encode, N unicast sends)"),
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("diagram_multicast_proposal.mmd", "diagram_multicast_proposal.png", "Proposed multicast setup (handshake then one media flow)"),
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]
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def render_mermaid() -> None:
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for mmd, png, _ in MM:
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src = BUILD / mmd
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dst = BUILD / png
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subprocess.run(
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[
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"npx",
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"--yes",
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"@mermaid-js/mermaid-cli@11.4.0",
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||||
"-i",
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str(src),
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"-o",
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str(dst),
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"-b",
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"white",
|
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"-w",
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"1400",
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"-H",
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"900",
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],
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cwd=str(ROOT),
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check=True,
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timeout=180,
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)
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def p(text: str, style) -> Paragraph:
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return Paragraph(text.replace("\n", "<br/>"), style)
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def build_pdf() -> None:
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styles = getSampleStyleSheet()
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title = ParagraphStyle(
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"DocTitle",
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parent=styles["Title"],
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fontSize=18,
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spaceAfter=12,
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textColor=colors.HexColor("#1565C0"),
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)
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h1 = ParagraphStyle("H1", parent=styles["Heading1"], fontSize=14, spaceBefore=14, spaceAfter=8)
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h2 = ParagraphStyle("H2", parent=styles["Heading2"], fontSize=12, spaceBefore=10, spaceAfter=6)
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body = ParagraphStyle("Body", parent=styles["Normal"], fontSize=10, leading=14, alignment=TA_LEFT)
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small = ParagraphStyle("Small", parent=body, fontSize=9, textColor=colors.grey)
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story = []
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story.append(p("Android Cast — Next-gen egress review", title))
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story.append(
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p(
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"Summary of sender 1:N behavior, bandwidth model, limitations, and feasibility "
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"of single-stream multicast plus multi-tier (full / 720p / 480p) renditions. "
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"Generated 2026-05-21.",
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small,
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)
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)
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story.append(Spacer(1, 0.4 * cm))
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# --- Current state ---
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story.append(p("1. Current sender behavior", h1))
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story.append(
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p(
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"<b>How many receivers?</b> Up to 5 when MULTI_RECEIVER_ENABLED "
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"(CastConfig.MAX_RECEIVERS). Sender opens one CastSession per selected device; "
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"failed handshakes are skipped if at least one peer connects.",
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body,
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)
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)
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story.append(Spacer(1, 0.2 * cm))
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story.append(
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p(
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"<b>CPU / GPU / memory:</b> Capture and encode run once per cast. "
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"CastFanoutPump duplicates each encoded frame to every session. "
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"Network send and per-peer UDP/FEC state scale with N; encode cost does not.",
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body,
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)
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)
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story.append(Spacer(1, 0.2 * cm))
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story.append(
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p(
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"<b>Bandwidth:</b> Per-receiver unicast duplicate of the same bitstream — not IP multicast. "
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"Rough LAN egress ≈ (video + ~96 kbps audio) × N, plus per-peer protocol overhead.",
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body,
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)
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)
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story.append(Spacer(1, 0.5 * cm))
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img1 = BUILD / MM[0][1]
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if img1.exists():
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story.append(p(MM[0][2], h2))
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iw = 16 * cm
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story.append(Image(str(img1), width=iw, height=iw * 0.45))
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story.append(Spacer(1, 0.4 * cm))
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# Table current limits
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story.append(p("1.1 Current limitations (sender-focused)", h2))
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limits = [
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["Area", "Limitation"],
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["Primary peer", "First connected peer sets negotiated MIME, adaptive tuning, and network feedback."],
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["Codec", "Single encoder; all peers must tolerate the same bitstream."],
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["Send path", "One CastFanoutPump thread; serial fan-out to N sessions."],
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["Wi‑Fi", "Uplink often saturates before CPU on 3–5 receivers."],
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["Topology", "Sender dials out; no shared LAN broadcast stream today."],
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]
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t = Table(limits, colWidths=[3.2 * cm, 13.3 * cm])
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t.setStyle(
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TableStyle(
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[
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("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1565C0")),
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("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
|
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("FONTNAME", (0, 0), (-1, 0), "Helvetica-Bold"),
|
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("FONTSIZE", (0, 0), (-1, -1), 9),
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("VALIGN", (0, 0), (-1, -1), "TOP"),
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("GRID", (0, 0), (-1, -1), 0.5, colors.lightgrey),
|
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("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F5F5F5")]),
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("LEFTPADDING", (0, 0), (-1, -1), 6),
|
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("RIGHTPADDING", (0, 0), (-1, -1), 6),
|
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("TOPPADDING", (0, 0), (-1, -1), 4),
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("BOTTOMPADDING", (0, 0), (-1, -1), 4),
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]
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)
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)
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story.append(t)
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story.append(PageBreak())
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# --- Proposal 1 ---
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story.append(p("2. Proposal: single outgoing stream (multicast)", h1))
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story.append(
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p(
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"<b>Goal:</b> One encoded stream on the air; only handshake-authorized receivers consume it; "
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"save ~(N−1) × bitrate vs today’s unicast fan-out.",
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body,
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)
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)
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story.append(Spacer(1, 0.2 * cm))
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story.append(
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p(
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"<b>Feasible</b> with UDP IP multicast + unicast handshake (group address, port, sessionId, PIN). "
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"Handshake-only targeting without multicast does <b>not</b> reduce bandwidth. "
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"TCP/QUIC cannot deliver true 1× Wi‑Fi airtime.",
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body,
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)
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)
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story.append(Spacer(1, 0.3 * cm))
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img2 = BUILD / MM[1][1]
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if img2.exists():
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story.append(p(MM[1][2], h2))
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iw = 16 * cm
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story.append(Image(str(img2), width=iw, height=iw * 0.55))
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story.append(Spacer(1, 0.4 * cm))
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story.append(p("2.1 Approach comparison", h2))
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approaches = [
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["Approach", "1× sender airtime?", "Notes"],
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["Unicast fan-out (today)", "No", "Same encode; N × send()."],
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["UDP multicast", "Yes on good LAN", "MulticastLock; AP client isolation risk."],
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["Sender server, N TCP clients", "No", "Flip connect direction; still N wire copies."],
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["LAN relay receiver", "Sender 1×", "Relay pays duplicate bandwidth."],
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]
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t2 = Table(approaches, colWidths=[4.5 * cm, 3.2 * cm, 8.8 * cm])
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t2.setStyle(
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TableStyle(
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[
|
||||
("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1565C0")),
|
||||
("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
|
||||
("FONTNAME", (0, 0), (-1, 0), "Helvetica-Bold"),
|
||||
("FONTSIZE", (0, 0), (-1, -1), 9),
|
||||
("VALIGN", (0, 0), (-1, -1), "TOP"),
|
||||
("GRID", (0, 0), (-1, -1), 0.5, colors.lightgrey),
|
||||
("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F5F5F5")]),
|
||||
("LEFTPADDING", (0, 0), (-1, -1), 6),
|
||||
("RIGHTPADDING", (0, 0), (-1, -1), 6),
|
||||
("TOPPADDING", (0, 0), (-1, -1), 4),
|
||||
("BOTTOMPADDING", (0, 0), (-1, -1), 4),
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||||
]
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)
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)
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story.append(t2)
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story.append(Spacer(1, 0.3 * cm))
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story.append(
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p(
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"<b>Protocol notes:</b> CastFramingContext.sessionId and CastSessionGate already support "
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"session binding. FEC/NACK must become group-scoped (one retransmit cache, resend to multicast). "
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"Existing code paths: MultiCastCoordinator, CastFanoutPump, UdpCastTransport.",
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body,
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)
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)
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story.append(PageBreak())
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# --- Proposal 2 ---
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story.append(p("3. Proposal: multi-tier streams (e.g. full + 720p + 480p)", h1))
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story.append(
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p(
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"<b>Goal:</b> Several encoded renditions from one capture; each receiver picks a tier at handshake "
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"(e.g. full quality vs 480p for bandwidth-limited devices).",
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body,
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)
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)
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story.append(Spacer(1, 0.2 * cm))
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story.append(
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p(
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"<b>Feasible</b> via multiple encoders fed from one capture (EGL / scaled Surfaces into separate "
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"MediaCodec instances). Cost scales with <b>active</b> tiers (~2–3 HW encoders typical phone limit; "
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"3× software VP9 is heavy). Audio usually stays one AAC stream.",
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body,
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)
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)
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story.append(Spacer(1, 0.2 * cm))
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story.append(
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p(
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"<b>Bandwidth:</b> Unicast per tier → egress ≈ sum of each peer’s tier bitrate. "
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"Multicast per tier → one group per tier; airtime ≈ sum of tiers with ≥1 subscriber.",
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body,
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)
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)
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story.append(Spacer(1, 0.3 * cm))
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story.append(p("3.1 Tier architecture options", h2))
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tiers = [
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["Option", "Verdict"],
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["Multiple HW encoders from one capture", "Recommended v1."],
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["One encode + CPU re-encode", "Too expensive for live cast."],
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["SVC / simulcast in one bitstream", "Poor Android HW support; defer."],
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["Receiver-only downscale", "Saves sender encode, not downlink bandwidth."],
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]
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t3 = Table(tiers, colWidths=[6 * cm, 10.5 * cm])
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t3.setStyle(
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TableStyle(
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[
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("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1565C0")),
|
||||
("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
|
||||
("FONTNAME", (0, 0), (-1, 0), "Helvetica-Bold"),
|
||||
("FONTSIZE", (0, 0), (-1, -1), 9),
|
||||
("GRID", (0, 0), (-1, -1), 0.5, colors.lightgrey),
|
||||
("VALIGN", (0, 0), (-1, -1), "TOP"),
|
||||
("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F5F5F5")]),
|
||||
("LEFTPADDING", (0, 0), (-1, -1), 6),
|
||||
("RIGHTPADDING", (0, 0), (-1, -1), 6),
|
||||
("TOPPADDING", (0, 0), (-1, -1), 4),
|
||||
("BOTTOMPADDING", (0, 0), (-1, -1), 4),
|
||||
]
|
||||
)
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||||
)
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story.append(t3)
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story.append(PageBreak())
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# --- Rollout ---
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story.append(p("4. Recommended rollout", h1))
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rollout = [
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["Phase", "Deliverable", "Benefit"],
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[
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"A — Tier selection (unicast)",
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"Handshake tier; 720p + 480p encoders; send chosen tier per peer",
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"Per-device quality without multicast; no AP surprises",
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],
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[
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"B — Multicast one tier",
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"UDP multicast publish after unicast handshake",
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"~(N−1) egress for same-quality 1:N",
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],
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[
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"C — Multicast per tier",
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"Separate multicast group per tier; lazy encoder start",
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"Combines (1) and (2) on good LANs",
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],
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]
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t4 = Table(rollout, colWidths=[3.5 * cm, 7.5 * cm, 5.5 * cm])
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||||
t4.setStyle(
|
||||
TableStyle(
|
||||
[
|
||||
("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1565C0")),
|
||||
("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
|
||||
("FONTNAME", (0, 0), (-1, 0), "Helvetica-Bold"),
|
||||
("FONTSIZE", (0, 0), (-1, -1), 9),
|
||||
("GRID", (0, 0), (-1, -1), 0.5, colors.lightgrey),
|
||||
("VALIGN", (0, 0), (-1, -1), "TOP"),
|
||||
("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F5F5F5")]),
|
||||
("LEFTPADDING", (0, 0), (-1, -1), 6),
|
||||
("RIGHTPADDING", (0, 0), (-1, -1), 6),
|
||||
("TOPPADDING", (0, 0), (-1, -1), 4),
|
||||
("BOTTOMPADDING", (0, 0), (-1, -1), 4),
|
||||
]
|
||||
)
|
||||
)
|
||||
story.append(t4)
|
||||
story.append(Spacer(1, 0.4 * cm))
|
||||
|
||||
story.append(p("4.1 Summary judgment", h2))
|
||||
summary = [
|
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["Idea", "Feasible?", "Main win", "Main cost"],
|
||||
[
|
||||
"(1) Multicast + handshake gate",
|
||||
"Yes (UDP)",
|
||||
"~(N−1) uplink on good LAN",
|
||||
"Transport refactor; FEC/NACK; AP testing",
|
||||
],
|
||||
["(1) Unicast only", "Trivial", "Auth only", "No bandwidth win"],
|
||||
["(2) Multi-tier encode", "Yes", "Per-receiver quality", "2–3× encode resources"],
|
||||
["(1) + (2) combined", "Yes", "Multicast per tier", "Highest complexity"],
|
||||
]
|
||||
t5 = Table(summary, colWidths=[4.2 * cm, 2.2 * cm, 4.5 * cm, 4.6 * cm])
|
||||
t5.setStyle(
|
||||
TableStyle(
|
||||
[
|
||||
("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1565C0")),
|
||||
("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
|
||||
("FONTNAME", (0, 0), (-1, 0), "Helvetica-Bold"),
|
||||
("FONTSIZE", (0, 0), (-1, -1), 8),
|
||||
("GRID", (0, 0), (-1, -1), 0.5, colors.lightgrey),
|
||||
("VALIGN", (0, 0), (-1, -1), "TOP"),
|
||||
("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F5F5F5")]),
|
||||
("LEFTPADDING", (0, 0), (-1, -1), 4),
|
||||
("RIGHTPADDING", (0, 0), (-1, -1), 4),
|
||||
("TOPPADDING", (0, 0), (-1, -1), 4),
|
||||
("BOTTOMPADDING", (0, 0), (-1, -1), 4),
|
||||
]
|
||||
)
|
||||
)
|
||||
story.append(t5)
|
||||
story.append(Spacer(1, 0.5 * cm))
|
||||
story.append(
|
||||
p(
|
||||
"<b>Key code paths today:</b> CastConfig.MAX_RECEIVERS, MultiCastCoordinator, "
|
||||
"CastFanoutPump, ScreenCastService (primary peer), UdpCastTransport, CastFramingContext, "
|
||||
"CastSessionGate.",
|
||||
small,
|
||||
)
|
||||
)
|
||||
|
||||
doc = SimpleDocTemplate(
|
||||
str(OUT_PDF),
|
||||
pagesize=A4,
|
||||
leftMargin=1.8 * cm,
|
||||
rightMargin=1.8 * cm,
|
||||
topMargin=1.5 * cm,
|
||||
bottomMargin=1.5 * cm,
|
||||
title="Android Cast — Next-gen egress review",
|
||||
author="Android Cast project",
|
||||
)
|
||||
doc.build(story)
|
||||
print(f"Wrote {OUT_PDF}")
|
||||
|
||||
|
||||
def main() -> int:
|
||||
render_mermaid()
|
||||
build_pdf()
|
||||
return 0
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
sys.exit(main())
|
||||
15
docs/_pdf_build/diagram_current_arch.mmd
Normal file
15
docs/_pdf_build/diagram_current_arch.mmd
Normal file
@@ -0,0 +1,15 @@
|
||||
flowchart LR
|
||||
subgraph once [Once per cast]
|
||||
Cap[MediaProjection capture]
|
||||
Enc[Video and audio encoders]
|
||||
Q[CastFanoutPump queues]
|
||||
end
|
||||
subgraph perPeer [Per receiver today]
|
||||
S1[CastSession 1 UDP or TCP]
|
||||
S2[CastSession 2]
|
||||
SN[CastSession N]
|
||||
end
|
||||
Cap --> Enc --> Q
|
||||
Q -->|same encoded payload| S1
|
||||
Q --> S2
|
||||
Q --> SN
|
||||
BIN
docs/_pdf_build/diagram_current_arch.png
Normal file
BIN
docs/_pdf_build/diagram_current_arch.png
Normal file
Binary file not shown.
|
After Width: | Height: | Size: 24 KiB |
9
docs/_pdf_build/diagram_multicast_proposal.mmd
Normal file
9
docs/_pdf_build/diagram_multicast_proposal.mmd
Normal file
@@ -0,0 +1,9 @@
|
||||
sequenceDiagram
|
||||
participant S as Sender
|
||||
participant R1 as Receiver 1
|
||||
participant R2 as Receiver N
|
||||
S->>R1: Unicast handshake PIN codec tier
|
||||
S->>R2: Unicast handshake
|
||||
Note over S: One encoder one sessionId
|
||||
S-->>R1: Multicast media packets
|
||||
S-->>R2: Same packets
|
||||
BIN
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Reference in New Issue
Block a user