From 50edef5bc13d0407aaaf26c951ce7a4a8cd4db58 Mon Sep 17 00:00:00 2001
From: Mark Felder <feld@feld.me>
Date: Fri, 29 Dec 2023 14:12:44 -0500
Subject: [PATCH] Change QTFastStart to recover gracefully if it encounters an
 error during bitstring matching

This fixes issues with internal errors when trying to serve the video
---
 changelog.d/qtfaststart.fix          |  1 +
 lib/pleroma/helpers/qt_fast_start.ex | 21 +++++++++++++--------
 2 files changed, 14 insertions(+), 8 deletions(-)
 create mode 100644 changelog.d/qtfaststart.fix

diff --git a/changelog.d/qtfaststart.fix b/changelog.d/qtfaststart.fix
new file mode 100644
index 000000000..66d2569f2
--- /dev/null
+++ b/changelog.d/qtfaststart.fix
@@ -0,0 +1 @@
+MediaProxy Preview failures prevented when encountering certain video files
diff --git a/lib/pleroma/helpers/qt_fast_start.ex b/lib/pleroma/helpers/qt_fast_start.ex
index 5711c7162..919fec84a 100644
--- a/lib/pleroma/helpers/qt_fast_start.ex
+++ b/lib/pleroma/helpers/qt_fast_start.ex
@@ -40,16 +40,21 @@ defp fix(
          got_mdat,
          acc
        ) do
-    full_size = (size - 8) * 8
-    <<data::bits-size(full_size), rest::bits>> = rest
+    try 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
-    ]
+      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)
+      fix(rest, pos + size, got_moov || fourcc == "moov", got_mdat || fourcc == "mdat", acc)
+    rescue
+      _ ->
+        :abort
+    end
   end
 
   defp fix(<<>>, _pos, _, _, acc) do