1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
|
# Pleroma: A lightweight social networking server
# Copyright © 2017-2020 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
|
