# Pleroma: A lightweight social networking server # Copyright © 2017-2021 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