From: Markus Fritsche <mfritsche@reauktion.de>
Subject: [PATCH 2/4] dom/media/platforms/ffmpeg: wrap
 av_hwdevice_ctx_create
Date: 2026-04-27

Background
----------
`FFmpegLibWrapper` already wraps `av_hwdevice_ctx_alloc` (no device
path) and `av_hwdevice_ctx_init`, used by the VAAPI codepath which
discovers the DRM device implicitly. The v4l2_request hwaccel needs
the *path-aware* constructor `av_hwdevice_ctx_create`, which lets the
caller pass `"/dev/dri/renderD128"` (or similar) directly when
creating an `AV_HWDEVICE_TYPE_DRM` context. libavcodec then binds the
v4l2_request hwaccel internally based on the codec's `hw_configs`.

This patch adds the function pointer + the `AV_FUNC_OPTION_SILENT`
registration. Same versioning as the other `av_hwdevice_ctx_*`
wrappers (libavutil 58–62). No callers yet — patch 3/4
(FFmpegVideoDecoder routing) consumes it.

Bug 1969297.

diff --git a/dom/media/platforms/ffmpeg/FFmpegLibWrapper.h b/dom/media/platforms/ffmpeg/FFmpegLibWrapper.h
--- a/dom/media/platforms/ffmpeg/FFmpegLibWrapper.h
+++ b/dom/media/platforms/ffmpeg/FFmpegLibWrapper.h
@@ -177,6 +177,11 @@
   // libavutil >= 58
   AVBufferRef* (*av_hwdevice_ctx_alloc)(int);
   int (*av_hwdevice_ctx_init)(AVBufferRef* ref);
+  // firefox-fourier: device-path-aware constructor needed to bind a
+  // DRM hwdevice (AV_HWDEVICE_TYPE_DRM) to /dev/dri/renderD* for the
+  // libavcodec v4l2_request hwaccel.
+  int (*av_hwdevice_ctx_create)(AVBufferRef** device_ctx, int type,
+                                const char* device, void* opts, int flags);
   AVBufferRef* (*av_hwframe_ctx_alloc)(AVBufferRef* device_ctx);
   int (*av_hwframe_ctx_init)(AVBufferRef* ref);
   AVBufferRef* (*av_buffer_ref)(AVBufferRef* buf);
diff --git a/dom/media/platforms/ffmpeg/FFmpegLibWrapper.cpp b/dom/media/platforms/ffmpeg/FFmpegLibWrapper.cpp
--- a/dom/media/platforms/ffmpeg/FFmpegLibWrapper.cpp
+++ b/dom/media/platforms/ffmpeg/FFmpegLibWrapper.cpp
@@ -293,6 +293,11 @@ FFmpegLibWrapper::LinkResult FFmpegLibWrapper::Link() {
                         AV_FUNC_AVUTIL_58 | AV_FUNC_AVUTIL_59 |
                             AV_FUNC_AVUTIL_60 | AV_FUNC_AVUTIL_61 |
                             AV_FUNC_AVUTIL_62)
+  // firefox-fourier: see comment in FFmpegLibWrapper.h
+  AV_FUNC_OPTION_SILENT(av_hwdevice_ctx_create,
+                        AV_FUNC_AVUTIL_58 | AV_FUNC_AVUTIL_59 |
+                            AV_FUNC_AVUTIL_60 | AV_FUNC_AVUTIL_61 |
+                            AV_FUNC_AVUTIL_62)
   AV_FUNC_OPTION_SILENT(
       av_buffer_ref, AV_FUNC_AVUTIL_58 | AV_FUNC_AVUTIL_59 | AV_FUNC_AVUTIL_60 |
                          AV_FUNC_AVUTIL_61 | AV_FUNC_AVUTIL_62)