From 3a4773c3c2bd0bbef244eb519b07208da9108e49 Mon Sep 17 00:00:00 2001
From: dcc <dcc@logografos.com>
Date: Sat, 2 Sep 2023 00:52:52 -0700
Subject: First

---
 lib/pleroma/helpers/qt_fast_start.ex | 131 +++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 lib/pleroma/helpers/qt_fast_start.ex

(limited to 'lib/pleroma/helpers/qt_fast_start.ex')

diff --git a/lib/pleroma/helpers/qt_fast_start.ex b/lib/pleroma/helpers/qt_fast_start.ex
new file mode 100644
index 0000000..5711c71
--- /dev/null
+++ b/lib/pleroma/helpers/qt_fast_start.ex
@@ -0,0 +1,131 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Helpers.QtFastStart do
+  @moduledoc """
+  (WIP) Converts a "slow start" (data before metadatas) mov/mp4 file to a "fast start" one (metadatas before data).
+  """
+
+  # TODO: Cleanup and optimizations
+  # Inspirations: https://www.ffmpeg.org/doxygen/3.4/qt-faststart_8c_source.html
+  #               https://github.com/danielgtaylor/qtfaststart/blob/master/qtfaststart/processor.py
+  #               ISO/IEC 14496-12:2015, ISO/IEC 15444-12:2015
+  #               Paracetamol
+
+  def fix(<<0x00, 0x00, 0x00, _, 0x66, 0x74, 0x79, 0x70, _::bits>> = binary) do
+    index = fix(binary, 0, nil, nil, [])
+
+    case index do
+      :abort -> binary
+      [{"ftyp", _, _, _, _}, {"mdat", _, _, _, _} | _] -> faststart(index)
+      [{"ftyp", _, _, _, _}, {"free", _, _, _, _}, {"mdat", _, _, _, _} | _] -> faststart(index)
+      _ -> binary
+    end
+  end
+
+  def fix(binary) do
+    binary
+  end
+
+  # MOOV have been seen before MDAT- abort
+  defp fix(<<_::bits>>, _, true, false, _) do
+    :abort
+  end
+
+  defp fix(
+         <<size::integer-big-size(32), fourcc::bits-size(32), rest::bits>>,
+         pos,
+         got_moov,
+         got_mdat,
+         acc
+       ) do
+    full_size = (size - 8) * 8
+    <<data::bits-size(full_size), rest::bits>> = rest
+
+    acc = [
+      {fourcc, pos, pos + size, size,
+       <<size::integer-big-size(32), fourcc::bits-size(32), data::bits>>}
+      | acc
+    ]
+
+    fix(rest, pos + size, got_moov || fourcc == "moov", got_mdat || fourcc == "mdat", acc)
+  end
+
+  defp fix(<<>>, _pos, _, _, acc) do
+    :lists.reverse(acc)
+  end
+
+  defp faststart(index) do
+    {{_ftyp, _, _, _, ftyp}, index} = List.keytake(index, "ftyp", 0)
+
+    # Skip re-writing the free fourcc as it's kind of useless.
+    # Why stream useless bytes when you can do without?
+    {free_size, index} =
+      case List.keytake(index, "free", 0) do
+        {{_, _, _, size, _}, index} -> {size, index}
+        _ -> {0, index}
+      end
+
+    {{_moov, _, _, moov_size, moov}, index} = List.keytake(index, "moov", 0)
+    offset = -free_size + moov_size
+    rest = for {_, _, _, _, data} <- index, do: data, into: []
+    <<moov_head::bits-size(64), moov_data::bits>> = moov
+    [ftyp, moov_head, fix_moov(moov_data, offset, []), rest]
+  end
+
+  defp fix_moov(
+         <<size::integer-big-size(32), fourcc::bits-size(32), rest::bits>>,
+         offset,
+         acc
+       ) do
+    full_size = (size - 8) * 8
+    <<data::bits-size(full_size), rest::bits>> = rest
+
+    data =
+      cond do
+        fourcc in ["trak", "mdia", "minf", "stbl"] ->
+          # Theses contains sto or co64 part
+          [<<size::integer-big-size(32), fourcc::bits-size(32)>>, fix_moov(data, offset, [])]
+
+        fourcc in ["stco", "co64"] ->
+          # fix the damn thing
+          <<version::integer-big-size(32), count::integer-big-size(32), rest::bits>> = data
+
+          entry_size =
+            case fourcc do
+              "stco" -> 32
+              "co64" -> 64
+            end
+
+          [
+            <<size::integer-big-size(32), fourcc::bits-size(32), version::integer-big-size(32),
+              count::integer-big-size(32)>>,
+            rewrite_entries(entry_size, offset, rest, [])
+          ]
+
+        true ->
+          [<<size::integer-big-size(32), fourcc::bits-size(32)>>, data]
+      end
+
+    acc = [acc | data]
+    fix_moov(rest, offset, acc)
+  end
+
+  defp fix_moov(<<>>, _, acc), do: acc
+
+  for size <- [32, 64] do
+    defp rewrite_entries(
+           unquote(size),
+           offset,
+           <<pos::integer-big-size(unquote(size)), rest::bits>>,
+           acc
+         ) do
+      rewrite_entries(unquote(size), offset, rest, [
+        acc | <<pos + offset::integer-big-size(unquote(size))>>
+      ])
+    end
+  end
+
+  defp rewrite_entries(_, _, <<>>, acc), do: acc
+end
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