catcrafts.net/tools/fetch-media.sh
Jorijn van der Graaf a625176c7d
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media: H.264 fallback beside every AV1, and the post links the H.264
The AV1-only publish lasted four hours in the wild: the first viewer on
mobile Safari got "bad media error" from the raw file, because a post's
link is fetched raw — Lemmy apps and browsers play that exact URL, with
no <source> negotiation in front of it. The previous commit's note
("--raw ... if that audience matters") had it backwards: the audience
that cannot play AV1 is not a per-post judgement call, it is whoever
happens to open the thread on an iPhone.

So publish-media.sh now emits two encodings and points the post at the
compatible one:

  * Every video transcode also produces <hash>.h264.mp4 (x264 crf 23,
    same denoise, same frames), uploaded beside the AV1 under the AV1's
    hash — the poster's sibling-naming trick, reused, so fetch-media.sh
    finds it by name with nothing to look up.
  * The printed URL to paste into the post is the H.264 one. pict-rs
    can thumbnail it too, so instance thumbnails come back as a bonus.

fetch-media.sh adopting an own-origin .h264.mp4 URL swaps the AV1 back
in as the page's primary when it is on the mount, and records the H.264
as `fallback` in posts.json. The renderer turns a non-empty fallback
into a <source> pair: the AV1 first with an explicit codecs parameter —
both files are video/mp4, so the parameter is the only thing that lets
a non-AV1 browser skip to the file it can play — and the H.264 second.
Browsers with AV1 keep downloading the small file; Safari before 17
gets one that plays instead of an element that will not.

e2e gains the matching conditional gate: a page offering an av01
<source> must offer an .h264.mp4 one, so an AV1 video can never again
ship without its fallback.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-08-08 03:14:51 +02:00

292 lines
13 KiB
Shell
Executable file

#!/bin/sh
# Mirror the media referenced by content/posts.json, and rewrite the entries to
# point at our own copies.
#
# Run AFTER tools/fetch-posts.sh, which records the original URLs.
#
# WHY MIRROR rather than embed from the source:
#
# * Privacy. The privacy notice states that everything the browser loads comes
# from catcrafts.net, and it should stay true. Embedding directly would send
# every visitor's IP address to whichever instance hosts the file — an odd
# thing to do on a site selling a privacy-focused phone.
# * Durability. These posts ARE their media: the screen recording of VoLTE
# working is the content. If the source instance deletes it or disappears,
# a direct embed becomes a broken box and the post loses its point.
# * Cost. One download per file, ever, instead of one per visitor. Kinder to
# small instances than hotlinking them.
#
# Files are content-addressed (sha256 of the bytes), so a file already present is
# never downloaded again and a changed file gets a new name — which makes the
# long cache lifetime Caddy sets honest.
#
# usage: tools/fetch-media.sh [media-dir] (default: media/)
#
# On any single download failure the entry keeps its original URL and the script
# carries on, so one dead file does not cost the whole page. Exits non-zero only
# if it cannot do its job at all.
set -eu
MEDIA_DIR="${1:-media}"
POSTS="content/posts.json"
MAX_BYTES=$((64 * 1024 * 1024))
# Media we host ourselves, published by tools/publish-media.sh before the post
# that carries it exists. Such a URL is ALREADY the one the page should use, so
# there is nothing to fetch: the bytes are on the media mount, and downloading
# them back from our own web server would only mint a second copy under a second
# name. Skipping the download also skips MAX_BYTES, which is what a 167 MB
# recording on a third-party file host ran into — and it removes the last part of
# a build that could fail because someone else's server was slow, rate-limiting
# or gone.
OWN_ORIGIN="https://catcrafts.net/media/"
command -v jq >/dev/null 2>&1 || { echo "fetch-media: jq not found" >&2; exit 1; }
[ -f "$POSTS" ] || { echo "fetch-media: $POSTS not found — run fetch-posts.sh first" >&2; exit 1; }
mkdir -p "$MEDIA_DIR"
# ffprobe gives real pixel dimensions, which become width/height attributes.
# Without them the browser cannot reserve space and the text below jumps as each
# image arrives; with them the layout is stable on first paint. Optional — the
# markup degrades to no dimensions rather than failing.
HAVE_FFPROBE=0
command -v ffprobe >/dev/null 2>&1 && HAVE_FFPROBE=1
# Sets $w and $h for the file named in $1, or leaves both 0.
#
# One query per dimension. Asking for both at once and splitting the CSV looked
# simpler but was wrong: for some files ffprobe appends an empty field, so
# `width,height` came back as "854x480x" and splitting on `x` gave a height of
# "480x" — which the digit guard below then threw away, silently costing the
# dimensions of exactly the videos that had the extra field. `nk=1` prints the
# bare value, so there is nothing to split.
#
# ROTATION: a phone records 1920x1080 and attaches a display matrix rather than
# rotating the pixels, so the stream reads landscape while the video plays
# portrait. Believing the stream there reserves a landscape box for a portrait
# video — precisely the layout shift these attributes exist to prevent — so a
# quarter-turn swaps them. Files that went through publish-media.sh have the
# rotation baked into the pixels and report no matrix at all; this is for
# anything mirrored straight from a phone.
probe_dims() {
w=0; h=0
[ "$HAVE_FFPROBE" = 1 ] || return 0
pw=$(ffprobe -v error -select_streams v:0 -show_entries stream=width \
-of default=nw=1:nk=1 "$1" 2>/dev/null | head -n1 || true)
ph=$(ffprobe -v error -select_streams v:0 -show_entries stream=height \
-of default=nw=1:nk=1 "$1" 2>/dev/null | head -n1 || true)
rot=$(ffprobe -v error -select_streams v:0 \
-show_entries stream_side_data=rotation \
-of default=nw=1:nk=1 "$1" 2>/dev/null | head -n1 || true)
case "$pw" in ''|*[!0-9]*) pw=0 ;; esac
case "$ph" in ''|*[!0-9]*) ph=0 ;; esac
# ffprobe reports this as a signed number that some builds print with a
# fractional part ("-90.000000"), so compare on the integer portion.
case "${rot%%.*}" in
90|-90|270|-270) t=$pw; pw=$ph; ph=$t ;;
esac
# Both or neither: a lone dimension is worse than none, because the browser
# derives the missing one from it and gets the aspect wrong.
if [ "$pw" -gt 0 ] && [ "$ph" -gt 0 ]; then w=$pw; h=$ph; fi
if [ "$w" = 0 ]; then
echo "fetch-media: no dimensions for $1; layout will shift on load" >&2
fi
}
MAP="$(mktemp)"
POSTERMAP="$(mktemp)"
FALLBACKMAP="$(mktemp)"
trap 'rm -f "$MAP" "$POSTERMAP" "$FALLBACKMAP"' EXIT
printf '[]' > "$MAP"
printf '[]' > "$POSTERMAP"
printf '[]' > "$FALLBACKMAP"
downloaded=0
reused=0
adopted=0
failed=0
# Every distinct media URL across all posts, so a file shared by two posts is
# fetched once. Video posters are in here too: a poster left pointing at the
# source instance would leak a visitor IP on page load exactly like an embedded
# image would, and it is the frame shown before anyone presses play.
#
# Fed by a here-document rather than a pipe so the counters below survive — in
# `jq | while`, the loop runs in a subshell and every increment is discarded.
while IFS= read -r src; do
[ -n "$src" ] || continue
# Ours already — adopt the file on the mount and do no network at all.
# A URL that is on our origin but names a file that is NOT on the mount is
# left alone rather than invented: that is a post published without its
# media, and keeping the original URL makes the e2e origin check fail
# loudly instead of shipping a 404 in a <video> tag.
case "$src" in
"$OWN_ORIGIN"*)
name=${src#"$OWN_ORIGIN"}
# Refuse anything that is not a bare filename. A path separator or a
# traversal segment arriving from a post URL must never reach a path we
# then read or publish.
case "$name" in
''|*/*|*..*)
echo "fetch-media: refusing suspicious own-origin URL: $src" >&2
failed=$((failed + 1)); continue ;;
esac
# A .h264.mp4 URL is the fediverse-facing form of an AV1 video: the
# post links the encoding everything can play, because that link is
# fetched raw by Lemmy apps. Our page can negotiate, so when the AV1
# sibling is on the mount it becomes the primary <source> and the
# H.264 drops to the fallback (picked up by name below).
case "$name" in
*.h264.mp4)
av1="${name%.h264.mp4}.mp4"
[ -f "$MEDIA_DIR/$av1" ] && name="$av1"
;;
esac
dest="$MEDIA_DIR/$name"
if [ ! -f "$dest" ]; then
echo "fetch-media: $name not on the media mount, keeping original URL: $src" >&2
failed=$((failed + 1)); continue
fi
adopted=$((adopted + 1))
;;
*)
ext=$(printf '%s' "$src" | sed -E 's/.*\.([A-Za-z0-9]+)$/\1/' | tr 'A-Z' 'a-z')
case "$ext" in
mp4|webm|mov|webp|png|jpg|jpeg|gif|avif) ;;
*) echo "fetch-media: skipping unexpected extension: $src" >&2; continue ;;
esac
tmp="$(mktemp)"
# --max-filesize refuses an oversized body before writing it; the explicit
# size check afterwards covers servers that do not send Content-Length.
if ! curl -fsSL --max-time 120 --max-filesize "$MAX_BYTES" \
-A 'catcrafts.net-buildfetch/1.0 (+https://catcrafts.net)' \
"$src" -o "$tmp" 2>/dev/null; then
echo "fetch-media: download failed, keeping original URL: $src" >&2
rm -f "$tmp"
failed=$((failed + 1))
continue
fi
if [ "$(wc -c < "$tmp")" -gt "$MAX_BYTES" ]; then
echo "fetch-media: oversized, keeping original URL: $src" >&2
rm -f "$tmp"
failed=$((failed + 1))
continue
fi
hash=$(sha256sum "$tmp" | cut -c1-16)
name="$hash.$ext"
dest="$MEDIA_DIR/$name"
if [ -f "$dest" ]; then
rm -f "$tmp"
reused=$((reused + 1))
else
mv "$tmp" "$dest"
chmod 0644 "$dest"
downloaded=$((downloaded + 1))
fi
;;
esac
probe_dims "$dest"
# A self-hosted video has no Lemmy thumbnail to mirror when the instance
# cannot decode it — AV1 is the common case, since pict-rs will not generate
# a still from one. publish-media.sh uploads a poster frame alongside the
# video under the video's own hash, so look for that sibling and offer it to
# the rewrite below. Without a poster a preload="metadata" video is a black
# box until someone presses play.
case "$name" in
*.mp4|*.webm|*.mov)
# Siblings are named after the AV1's hash, so strip the .h264
# marker too — a video adopted as X.h264.mp4 (its AV1 never
# published) still finds X.poster.webp.
base="${name%.*}"
base="${base%.h264}"
sibling="$base.poster.webp"
if [ -f "$MEDIA_DIR/$sibling" ]; then
jq --arg k "/media/$name" --arg v "/media/$sibling" \
'. + [{key: $k, value: $v}]' "$POSTERMAP" > "$POSTERMAP.new" \
&& mv "$POSTERMAP.new" "$POSTERMAP"
fi
# The H.264 sibling publish-media.sh uploaded next to the AV1.
# Rendered as a second <source> so browsers without AV1 (Safari
# before 17, Apple hardware without the decoder) get a file they
# can play instead of an element that will not. The guard against
# naming itself covers a video adopted as X.h264.mp4 whose AV1 is
# not on the mount.
fb="$base.h264.mp4"
if [ "$fb" != "$name" ] && [ -f "$MEDIA_DIR/$fb" ]; then
jq --arg k "/media/$name" --arg v "/media/$fb" \
'. + [{key: $k, value: $v}]' "$FALLBACKMAP" > "$FALLBACKMAP.new" \
&& mv "$FALLBACKMAP.new" "$FALLBACKMAP"
fi
;;
esac
jq --arg src "$src" --arg path "/media/$name" \
--argjson w "${w:-0}" --argjson h "${h:-0}" \
'. + [{src: $src, path: $path, w: $w, h: $h}]' "$MAP" > "$MAP.new" \
&& mv "$MAP.new" "$MAP"
done <<EOF
$(jq -r '[.[].media[]? | .src, (.poster // empty)] | map(select(. != "")) | unique[]' "$POSTS")
EOF
echo "fetch-media: $downloaded new, $reused already present, $adopted self-hosted, $failed failed"
# Rewrite each media entry to the local path. An entry with no mapping (download
# failed) keeps its original src, so the page still shows something rather than
# silently dropping the post's whole point.
TMP_POSTS="$(mktemp)"
if jq --slurpfile map "$MAP" --slurpfile posters "$POSTERMAP" \
--slurpfile fallbacks "$FALLBACKMAP" '
($map[0] | map({key: .src, value: .}) | from_entries) as $m
| ($posters[0] | from_entries) as $pm
| ($fallbacks[0] | from_entries) as $fm
| map(.media = ((.media // []) | map(
. as $item
| ($m[$item.src] // null) as $hit
| (if $hit == null then $item
else $item + { src: $hit.path, w: $hit.w, h: $hit.h }
end)
# The poster gets its path rewritten but NOT its dimensions: w/h describe
# the video, and a poster is a differently-sized still of it. Feeding the
# poster'\''s size to the <video> element would set the wrong aspect ratio.
| if (.poster // "") == "" then .
else . + { poster: (($m[.poster].path) // .poster) }
end
# Last resort, and only for media we host: the sibling poster frame
# publish-media.sh uploaded next to the video. Runs after the rewrite
# above so it sees the LOCAL src, and only fills a poster that is still
# empty — a thumbnail the instance did provide always wins.
| if ((.poster // "") == "") and (($pm[.src] // "") != "")
then . + { poster: $pm[.src] }
else . end
# H.264 fallback, keyed by the LOCAL src like the poster map. Only ever
# set for media on our own mount — a mirrored third-party file has no
# sibling to find.
| if (($fm[.src] // "") != "")
then . + { fallback: $fm[.src] }
else . end)))
' "$POSTS" > "$TMP_POSTS" 2>/dev/null; then
# Same reason as the chmod on each mirrored file: mktemp is 0600 and the
# mode survives to production, where other users must read this.
chmod 0644 "$TMP_POSTS"
mv "$TMP_POSTS" "$POSTS"
else
rm -f "$TMP_POSTS"
echo "fetch-media: could not rewrite $POSTS, leaving it unchanged" >&2
exit 1
fi
total=$(jq '[.[].media[]? | .src, (.poster // empty) | select(. != "")] | length' "$POSTS")
local_count=$(jq '[.[].media[]? | .src, (.poster // empty)
| select(startswith("/media/"))] | length' "$POSTS")
echo "fetch-media: $local_count of $total media entries served locally ($(du -sh "$MEDIA_DIR" | cut -f1) in $MEDIA_DIR)"
if [ "$local_count" -ne "$total" ]; then
echo "fetch-media: $((total - local_count)) still point at their source — see the failures above" >&2
fi