Fix oban tags
[akkoma] / lib / pleroma / helpers / qt_fast_start.ex
1 # Pleroma: A lightweight social networking server
2 # Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
3 # SPDX-License-Identifier: AGPL-3.0-only
4
5 defmodule Pleroma.Helpers.QtFastStart do
6 @moduledoc """
7 (WIP) Converts a "slow start" (data before metadatas) mov/mp4 file to a "fast start" one (metadatas before data).
8 """
9
10 # TODO: Cleanup and optimizations
11 # Inspirations: https://www.ffmpeg.org/doxygen/3.4/qt-faststart_8c_source.html
12 # https://github.com/danielgtaylor/qtfaststart/blob/master/qtfaststart/processor.py
13 # ISO/IEC 14496-12:2015, ISO/IEC 15444-12:2015
14 # Paracetamol
15
16 def fix(<<0x00, 0x00, 0x00, _, 0x66, 0x74, 0x79, 0x70, _::bits>> = binary) do
17 index = fix(binary, 0, nil, nil, [])
18
19 case index do
20 :abort -> binary
21 [{"ftyp", _, _, _, _}, {"mdat", _, _, _, _} | _] -> faststart(index)
22 [{"ftyp", _, _, _, _}, {"free", _, _, _, _}, {"mdat", _, _, _, _} | _] -> faststart(index)
23 _ -> binary
24 end
25 end
26
27 def fix(binary) do
28 binary
29 end
30
31 # MOOV have been seen before MDAT- abort
32 defp fix(<<_::bits>>, _, true, false, _) do
33 :abort
34 end
35
36 defp fix(
37 <<size::integer-big-size(32), fourcc::bits-size(32), rest::bits>>,
38 pos,
39 got_moov,
40 got_mdat,
41 acc
42 ) do
43 full_size = (size - 8) * 8
44 <<data::bits-size(full_size), rest::bits>> = rest
45
46 acc = [
47 {fourcc, pos, pos + size, size,
48 <<size::integer-big-size(32), fourcc::bits-size(32), data::bits>>}
49 | acc
50 ]
51
52 fix(rest, pos + size, got_moov || fourcc == "moov", got_mdat || fourcc == "mdat", acc)
53 end
54
55 defp fix(<<>>, _pos, _, _, acc) do
56 :lists.reverse(acc)
57 end
58
59 defp faststart(index) do
60 {{_ftyp, _, _, _, ftyp}, index} = List.keytake(index, "ftyp", 0)
61
62 # Skip re-writing the free fourcc as it's kind of useless.
63 # Why stream useless bytes when you can do without?
64 {free_size, index} =
65 case List.keytake(index, "free", 0) do
66 {{_, _, _, size, _}, index} -> {size, index}
67 _ -> {0, index}
68 end
69
70 {{_moov, _, _, moov_size, moov}, index} = List.keytake(index, "moov", 0)
71 offset = -free_size + moov_size
72 rest = for {_, _, _, _, data} <- index, do: data, into: []
73 <<moov_head::bits-size(64), moov_data::bits>> = moov
74 [ftyp, moov_head, fix_moov(moov_data, offset, []), rest]
75 end
76
77 defp fix_moov(
78 <<size::integer-big-size(32), fourcc::bits-size(32), rest::bits>>,
79 offset,
80 acc
81 ) do
82 full_size = (size - 8) * 8
83 <<data::bits-size(full_size), rest::bits>> = rest
84
85 data =
86 cond do
87 fourcc in ["trak", "mdia", "minf", "stbl"] ->
88 # Theses contains sto or co64 part
89 [<<size::integer-big-size(32), fourcc::bits-size(32)>>, fix_moov(data, offset, [])]
90
91 fourcc in ["stco", "co64"] ->
92 # fix the damn thing
93 <<version::integer-big-size(32), count::integer-big-size(32), rest::bits>> = data
94
95 entry_size =
96 case fourcc do
97 "stco" -> 32
98 "co64" -> 64
99 end
100
101 [
102 <<size::integer-big-size(32), fourcc::bits-size(32), version::integer-big-size(32),
103 count::integer-big-size(32)>>,
104 rewrite_entries(entry_size, offset, rest, [])
105 ]
106
107 true ->
108 [<<size::integer-big-size(32), fourcc::bits-size(32)>>, data]
109 end
110
111 acc = [acc | data]
112 fix_moov(rest, offset, acc)
113 end
114
115 defp fix_moov(<<>>, _, acc), do: acc
116
117 for size <- [32, 64] do
118 defp rewrite_entries(
119 unquote(size),
120 offset,
121 <<pos::integer-big-size(unquote(size)), rest::bits>>,
122 acc
123 ) do
124 rewrite_entries(unquote(size), offset, rest, [
125 acc | <<pos + offset::integer-big-size(unquote(size))>>
126 ])
127 end
128 end
129
130 defp rewrite_entries(_, _, <<>>, acc), do: acc
131 end