From 41dfcbbacfa9232d2308d0229dcd172309b32f9f Mon Sep 17 00:00:00 2001
From: Lynne <dev@lynne.ee>
Date: Mon, 30 Oct 2023 05:38:17 +0100
Subject: [PATCH 1/2] decode: add ff_decode_skip_samples function

This is a convenience function, which is required to be called by decoders
needing to skip samples every time.
It automatically creates and increments side data.

The idea is to get rid of skip_samples eventually and replace it with this
function.
---
 libavcodec/decode.c | 18 ++++++++++++++++++
 libavcodec/decode.h |  9 +++++++++
 2 files changed, 27 insertions(+)

diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index ad39021354..f971723ff7 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -299,6 +299,24 @@ static int64_t guess_correct_pts(AVCodecContext *ctx,
     return pts;
 }
 
+int ff_decode_skip_samples(AVCodecContext *avctx, AVFrame *frame, uint32_t base_skip, uint32_t additional)
+{
+    uint32_t val = 0;
+    AVFrameSideData *side = av_frame_get_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES);
+    if (!side) {
+        side = av_frame_new_side_data(frame, AV_FRAME_DATA_SKIP_SAMPLES, 10);
+        if (!side)
+            return AVERROR(ENOMEM);
+        AV_WL32(side->data, base_skip);
+    }
+
+    val += AV_RL32(side->data);
+    val += additional;
+    AV_WL32(side->data, val);
+
+    return 0;
+}
+
 static int discard_samples(AVCodecContext *avctx, AVFrame *frame, int64_t *discarded_samples)
 {
     AVCodecInternal *avci = avctx->internal;
diff --git a/libavcodec/decode.h b/libavcodec/decode.h
index daf1a67444..647f091da9 100644
--- a/libavcodec/decode.h
+++ b/libavcodec/decode.h
@@ -155,4 +155,13 @@ int ff_hwaccel_frame_priv_alloc(AVCodecContext *avctx, void **hwaccel_picture_pr
 const AVPacketSideData *ff_get_coded_side_data(const AVCodecContext *avctx,
                                                enum AVPacketSideDataType type);
 
+/**
+ * Skip samples in an AVFrame.
+ *
+ * @param base_skip amount of samples to skip if no side data is present
+ * @param additional amount of samples to skip unconditionally
+ */
+int ff_decode_skip_samples(AVCodecContext *avctx, AVFrame *frame,
+                           uint32_t base_skip, uint32_t additional);
+
 #endif /* AVCODEC_DECODE_H */
-- 
2.42.0