[FFmpeg-devel] [PATCH] avcodec/videotoolboxenc: support global_quality without qscale (PR #20382)

[Zhao Zhili via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20382 opened by Zhao Zhili (quink)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20382
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20382.patch


>From 2e680445ec3975462e4ba3af0e8e1840b0e03bf1 Mon Sep 17 00:00:00 2001
From: Zhao Zhili <zhilizhao@tencent.com>
Date: Mon, 1 Sep 2025 01:17:08 +0800
Subject: [PATCH 1/2] avcodec/videotoolboxenc: fix the loss of precision when
 calculating quality

---
 libavcodec/videotoolboxenc.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/libavcodec/videotoolboxenc.c b/libavcodec/videotoolboxenc.c
index b748ecda61..ff8e636c88 100644
--- a/libavcodec/videotoolboxenc.c
+++ b/libavcodec/videotoolboxenc.c
@@ -1185,9 +1185,7 @@ static int vtenc_create_encoder(AVCodecContext   *avctx,
     VTEncContext *vtctx = avctx->priv_data;
     SInt32       bit_rate = avctx->bit_rate;
     SInt32       max_rate = avctx->rc_max_rate;
-    Float32      quality = avctx->global_quality / FF_QP2LAMBDA;
     CFNumberRef  bit_rate_num;
-    CFNumberRef  quality_num;
     CFNumberRef  bytes_per_second;
     CFNumberRef  one_second;
     CFArrayRef   data_rate_limits;
@@ -1248,10 +1246,11 @@ static int vtenc_create_encoder(AVCodecContext   *avctx,
     }
 
     if (avctx->flags & AV_CODEC_FLAG_QSCALE) {
-        quality = quality >= 100 ? 1.0 : quality / 100;
-        quality_num = CFNumberCreate(kCFAllocatorDefault,
-                                     kCFNumberFloat32Type,
-                                     &quality);
+        Float32 quality = FFMIN(avctx->global_quality / 100.0f / FF_QP2LAMBDA,
+                                1.0f);
+        CFNumberRef quality_num = CFNumberCreate(kCFAllocatorDefault,
+                                                 kCFNumberFloat32Type,
+                                                 &quality);
         if (!quality_num) return AVERROR(ENOMEM);
 
         status = VTSessionSetProperty(vtctx->session,
-- 
2.49.1


>From 8ea46fe2abcc2c9417707d7b130c99e4546e75dc Mon Sep 17 00:00:00 2001
From: Zhao Zhili <zhilizhao@tencent.com>
Date: Mon, 1 Sep 2025 01:36:25 +0800
Subject: [PATCH 2/2] avcodec/videotoolboxenc: support global_quality without
 qscale

---
 libavcodec/videotoolboxenc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libavcodec/videotoolboxenc.c b/libavcodec/videotoolboxenc.c
index ff8e636c88..ef8a729992 100644
--- a/libavcodec/videotoolboxenc.c
+++ b/libavcodec/videotoolboxenc.c
@@ -1245,9 +1245,10 @@ static int vtenc_create_encoder(AVCodecContext   *avctx,
         return AVERROR_EXTERNAL;
     }
 
-    if (avctx->flags & AV_CODEC_FLAG_QSCALE) {
-        Float32 quality = FFMIN(avctx->global_quality / 100.0f / FF_QP2LAMBDA,
-                                1.0f);
+    if (avctx->flags & AV_CODEC_FLAG_QSCALE || avctx->global_quality > 0) {
+        float factor = (avctx->flags & AV_CODEC_FLAG_QSCALE) ?
+                       FF_QP2LAMBDA * 100.0f : 100.0f;
+        Float32 quality = FFMIN(avctx->global_quality / factor, 1.0f);
         CFNumberRef quality_num = CFNumberCreate(kCFAllocatorDefault,
                                                  kCFNumberFloat32Type,
                                                  &quality);
-- 
2.49.1

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