fix(ffmpeg): Add upstreamed MF low latency encoding patch (#587)

Author: cgutman

patches/FFmpeg/FFmpeg/MF/01-mfenc-lowlatency.patch

@@ -1,64 +1,28 @@
+From 126671e73065e29c9582e47bc74774af2200fc8f Mon Sep 17 00:00:00 2001
 From: Cameron Gutman <aicommander@gmail.com>
-To: ffmpeg-devel@ffmpeg.org
-Date: Sat,  2 Aug 2025 23:55:25 -0500
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-Subject: [FFmpeg-devel] [PATCH] avcodec/mfenc: add low_latency encoder
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-Cc: Conn O'Griofa <connogriofa@gmail.com>
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+Date: Sun, 31 Aug 2025 16:05:15 -0500
+Subject: [PATCH] avcodec/mfenc: add AVLowLatencyMode support
 
-Implement support for CODECAPI_AVLowLatencyMode property, which is
-useful for live streaming use cases (and cannot be achieved by
-selecting any of the low latency "scenario" encoder presets alone).
+Set CODECAPI_AVLowLatencyMode when AV_CODEC_FLAG_LOW_DELAY is enabled on
+the AVCodecContext. AVLowLatencyMode can acheive lower latency encoding
+that may not be accessible using eAVScenarioInfo options alone.
 
-Co-authored-by: Conn O'Griofa <connogriofa@gmail.com>
 Signed-off-by: Cameron Gutman <aicommander@gmail.com>
 ---
- libavcodec/mfenc.c | 5 +++++
- 1 file changed, 5 insertions(+)
+ libavcodec/mfenc.c | 3 +++
+ 1 file changed, 3 insertions(+)
 
 diff --git a/libavcodec/mfenc.c b/libavcodec/mfenc.c
-index 30531fe3e8..e84ce7bde0 100644
+index 6f79386404502..541f7fb9612af 100644
 --- a/libavcodec/mfenc.c
 +++ b/libavcodec/mfenc.c
-@@ -64,6 +64,7 @@ typedef struct MFContext {
-     int opt_enc_quality;
-     int opt_enc_scenario;
-     int opt_enc_hw;
-+    int opt_enc_lowlatency;
-     AVD3D11VADeviceContext* device_hwctx;
- } MFContext;
- 
-@@ -866,6 +867,9 @@ static int mf_encv_output_adjust(AVCodecContext *avctx, IMFMediaType *type)
- 
+@@ -876,6 +876,9 @@ static int mf_encv_output_adjust(AVCodecContext *avctx, IMFMediaType *type)
+
          if (c->opt_enc_scenario >= 0)
              ICodecAPI_SetValue(c->codec_api, &ff_CODECAPI_AVScenarioInfo, FF_VAL_VT_UI4(c->opt_enc_scenario));
 +
-+        if (c->opt_enc_lowlatency)
++        if (avctx->flags & AV_CODEC_FLAG_LOW_DELAY)
 +            ICodecAPI_SetValue(c->codec_api, &ff_CODECAPI_AVLowLatencyMode, FF_VAL_VT_UI4(1));
      }
- 
+
      return 0;
-@@ -1445,6 +1449,7 @@ static const AVOption venc_opts[] = {
- 
-     {"quality",       "Quality", OFFSET(opt_enc_quality), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 100, VE},
-     {"hw_encoding",   "Force hardware encoding", OFFSET(opt_enc_hw), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, VE},
-+    {"low_latency",   "Low latency mode", OFFSET(opt_enc_lowlatency), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, VE},
-     {NULL}
- };
-