[PATCH RFC 01/11] media: h264: Only write the SPS and PPS of a stateless encode when they change

[Arun Iyengar via B4 Relay <devnull+aiyengar1990.gmail.com@kernel.org>]

From: Arun Iyengar <aiyengar1990@gmail.com>

The stateless encode core is meant to write the SPS and PPS for the first
picture of a stream, and then only when they change. The check is
inverted: the first picture compares the new SPS and PPS with the zeroed
active state, which always differs, and all the following pictures get
them unconditionally. This wastes some bits on every picture, and skews
the size statistics of the rate control.

Compare with the active state once a picture was encoded, and write them
unconditionally for the first picture. The
V4L2_CID_MPEG_VIDEO_PREPEND_SPSPPS_TO_IDR control still forces them on
IDR pictures.

To be squashed into "media: h264: Add stateless encode core" from
https://patch.msgid.link/20260522101653.2565125-5-paulk@sys-base.io

Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
---
 drivers/media/v4l2-core/v4l2-h264-enc.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-h264-enc.c b/drivers/media/v4l2-core/v4l2-h264-enc.c
index 67ea82cebe7f..af925b6626cf 100644
--- a/drivers/media/v4l2-core/v4l2-h264-enc.c
+++ b/drivers/media/v4l2-core/v4l2-h264-enc.c
@@ -762,9 +762,12 @@ static int rbsp_update(struct v4l2_h264_enc *enc)
 	if (ctrl && ctrl->cur.val)
 		enc->rbsp_update |= V4L2_H264_ENC_RBSP_UPDATE_AUD;
 
-	/* SPS */
+	/*
+	 * SPS: always written for the first picture of the stream, then only
+	 * when it changes.
+	 */
 
-	if (!enc->state_serial) {
+	if (enc->state_serial) {
 		if (memcmp(&state_active->sps, &state->sps,
 			   sizeof(state_active->sps)) ||
 		    memcmp(&state_active->sps_video, &state->sps_video,
@@ -774,9 +777,9 @@ static int rbsp_update(struct v4l2_h264_enc *enc)
 		enc->rbsp_update |= V4L2_H264_ENC_RBSP_UPDATE_SPS;
 	}
 
-	/* PPS */
+	/* PPS: same as the SPS. */
 
-	if (!enc->state_serial) {
+	if (enc->state_serial) {
 		if (memcmp(&state_active->pps, &state->pps,
 			   sizeof(state_active->pps)))
 			enc->rbsp_update |= V4L2_H264_ENC_RBSP_UPDATE_PPS;

-- 
2.55.0