LibWeb: Implement some of SourceBuffer.appendBuffer()

Currently, it just fires the error event immediately.

Libraries/LibWeb/MediaSourceExtensions/SourceBufferProcessor.cpp

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2026-present, the Ladybird developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Format.h>
+#include <LibWeb/MediaSourceExtensions/SourceBufferProcessor.h>
+
+namespace Web::MediaSourceExtensions {
+
+SourceBufferProcessor::SourceBufferProcessor()
+{
+}
+SourceBufferProcessor::~SourceBufferProcessor() = default;
+
+AppendMode SourceBufferProcessor::mode() const
+{
+    return m_mode;
+}
+
+bool SourceBufferProcessor::is_buffer_full() const
+{
+    return m_buffer_full_flag;
+}
+
+void SourceBufferProcessor::set_append_error_callback(AppendErrorCallback callback)
+{
+    m_append_error_callback = move(callback);
+}
+
+void SourceBufferProcessor::append_to_input_buffer(ReadonlyBytes bytes)
+{
+    m_input_buffer.append(bytes);
+}
+
+// https://w3c.github.io/media-source/#sourcebuffer-segment-parser-loop
+void SourceBufferProcessor::run_segment_parser_loop()
+{
+    m_append_error_callback();
+}
+
+// https://w3c.github.io/media-source/#sourcebuffer-reset-parser-state
+void SourceBufferProcessor::reset_parser_state()
+{
+    // 1. If the [[append state]] equals PARSING_MEDIA_SEGMENT and the [[input buffer]] contains some
+    //    complete coded frames, then run the coded frame processing algorithm until all of these
+    //    complete coded frames have been processed.
+    if (m_append_state == AppendState::ParsingMediaSegment) {
+        // FIXME: Process any complete coded frames
+    }
+
+    // FIXME: 2. Unset the last decode timestamp on all track buffers.
+    // FIXME: 3. Unset the last frame duration on all track buffers.
+    // FIXME: 4. Unset the highest end timestamp on all track buffers.
+
+    // FIXME: 5. Set the need random access point flag on all track buffers to true.
+
+    // 6. If the mode attribute equals "sequence", then
+    if (m_mode == AppendMode::Sequence) {
+        // FIXME: set the [[group start timestamp]] to the [[group end timestamp]]
+    }
+
+    // 7. Remove all bytes from the [[input buffer]].
+    m_input_buffer.clear();
+
+    // 8. Set [[append state]] to WAITING_FOR_SEGMENT.
+    m_append_state = AppendState::WaitingForSegment;
+}
+
+// https://w3c.github.io/media-source/#sourcebuffer-coded-frame-eviction
+void SourceBufferProcessor::run_coded_frame_eviction()
+{
+    // FIXME: 1. Let new data equal the data that is about to be appended to this SourceBuffer.
+    //        2. If the [[buffer full flag]] equals false, then abort these steps.
+    //        3. Let removal ranges equal a list of presentation time ranges that can be evicted from the presentation
+    //           to make room for the new data.
+    //        4. For each range in removal ranges, run the coded frame removal algorithm with start and end equal to
+    //           the removal range start and end timestamp respectively.
+}
+
+}