Add --sframe-replace-kf encoder parameter

apps/avmenc.c

@@ -1180,6 +1180,8 @@ static int parse_stream_params(struct AvxEncoderConfig *global,
       config->cfg.sframe_mode = arg_parse_uint(&arg);
     } else if (arg_match(&arg, &g_av2_codec_arg_defs.sframe_type, argi)) {
       config->cfg.sframe_type = arg_parse_uint(&arg);
+    } else if (arg_match(&arg, &g_av2_codec_arg_defs.sframe_replace_kf, argi)) {
+      config->cfg.sframe_replace_kf = arg_parse_uint(&arg);
     } else if (arg_match(&arg, &g_av2_codec_arg_defs.enable_lcr, argi)) {
       config->cfg.enable_lcr = arg_parse_uint(&arg);
     } else if (arg_match(&arg, &g_av2_codec_arg_defs.enable_ops, argi)) {

av2/arg_defs.c

@@ -289,6 +289,9 @@ const av2_codec_arg_definitions_t g_av2_codec_arg_defs = {
       ARG_DEF(NULL, "sframe-mode", 1, "S-Frame insertion mode (0..2)"),
   .sframe_type = ARG_DEF(NULL, "sframe-type", 1,
                          "(0: Regular S-Frame (default), 1: RAS frame)"),
+  .sframe_replace_kf =
+      ARG_DEF(NULL, "sframe-replace-kf", 1,
+              "Replace N consecutive keyframes with S-frames (0: off)"),
   .enable_lcr =
       ARG_DEF(NULL, "enable-lcr", 1,
               "Enable layer config record (LCR) OBU (0: off (default), 1: on)"),

av2/arg_defs.h

@@ -108,6 +108,7 @@ typedef struct av2_codec_arg_definitions {
   arg_def_t sframe_dist;
   arg_def_t sframe_mode;
   arg_def_t sframe_type;
+  arg_def_t sframe_replace_kf;
   arg_def_t enable_lcr;
   arg_def_t enable_ops;
   arg_def_t num_ops;

av2/av2_cx_iface.c

@@ -1523,6 +1523,7 @@ static avm_codec_err_t set_encoder_config(AV2EncoderConfig *oxcf,
   kf_cfg->sframe_dist = cfg->sframe_dist;
   kf_cfg->sframe_mode = cfg->sframe_mode;
   kf_cfg->sframe_type = cfg->sframe_type;
+  kf_cfg->sframe_replace_kf = cfg->sframe_replace_kf;
   oxcf->unit_test_cfg.insert_sframe = extra_cfg->enable_sframe;
 
   kf_cfg->enable_keyframe_filtering = extra_cfg->enable_keyframe_filtering;
@@ -4782,6 +4783,7 @@ static const avm_codec_enc_cfg_t encoder_usage_cfg[] = { {
     0,                           // sframe_dist
     1,                           // sframe_mode
     0,                           // sframe_type
+    1,                           // sframe_replace_kf
     0,                           // monochrome
     0,                           // full_still_picture_hdr
     1,                           // enable_tcq

av2/encoder/encode_strategy.c

@@ -1277,6 +1277,7 @@ int av2_encode_strategy(AV2_COMP *const cpi, size_t *const size,
 
   cm->restricted_prediction_switch =
       (cpi->oxcf.kf_cfg.enable_sframe && cpi->oxcf.kf_cfg.sframe_mode == 0) ||
+      (cpi->oxcf.kf_cfg.sframe_replace_kf > 0 && cpi->oxcf.kf_cfg.sframe_mode == 0) ||
       cpi->oxcf.tool_cfg.g_error_resilient_mode;
 
   av2_configure_buffer_updates(cpi, frame_update_type);

av2/encoder/encoder.c

@@ -5102,6 +5102,7 @@ int av2_encode(AV2_COMP *const cpi, uint8_t *const dest,
   current_frame->mlayer_id = cm->mlayer_id;
   cm->restricted_prediction_switch =
       (cpi->oxcf.kf_cfg.enable_sframe && cpi->oxcf.kf_cfg.sframe_mode == 0) ||
+      (cpi->oxcf.kf_cfg.sframe_replace_kf > 0 && cpi->oxcf.kf_cfg.sframe_mode == 0) ||
       cpi->oxcf.tool_cfg.g_error_resilient_mode;
   if (current_frame->frame_type == KEY_FRAME) {
     for (int i = 0; i < cm->seq_params.ref_frames; i++) {

av2/encoder/encoder.h

@@ -438,6 +438,12 @@ typedef struct {
    */
   bool enable_sframe;
 
+  /*!
+   * Number of consecutive keyframes to replace with S-frames between actual
+   * keyframes.
+   */
+  int sframe_replace_kf;
+
   /*!
    * Indicates if intra block copy prediction mode should be enabled or not.
    */

av2/encoder/pass2_strategy.c

@@ -2930,6 +2930,17 @@ void av2_get_second_pass_params(AV2_COMP *cpi,
       frame_params->frame_type = KEY_FRAME;
       if (frame_params->frame_params_obu_type == NUM_OBU_TYPES)
         frame_params->frame_params_obu_type = OBU_CLOSED_LOOP_KEY;
+      const int replace_kf = oxcf->kf_cfg.sframe_replace_kf;
+      if (replace_kf > 0 && cpi->common.current_frame.frame_number > 0) {
+        rc->sframe_replace_kf_count++;
+        if (rc->sframe_replace_kf_count <= replace_kf) {
+          frame_params->frame_type = S_FRAME;
+          frame_params->frame_params_obu_type = NUM_OBU_TYPES;
+          cpi->is_ras_frame = (oxcf->kf_cfg.sframe_type == RAS_FRAME);
+        } else {
+          rc->sframe_replace_kf_count = 0;
+        }
+      }
       // Define next KF group and assign bits to it.
       find_next_key_frame(cpi, &this_frame);
     }

av2/encoder/ratectrl.h

@@ -186,6 +186,7 @@ typedef struct {
   int next_key_frame_forced;
   int is_src_frame_alt_ref;
   int sframe_due;
+  int sframe_replace_kf_count;
 
   int high_source_sad;
   uint64_t avg_source_sad;

avm/avm_encoder.h

@@ -1064,6 +1064,13 @@ typedef struct avm_codec_enc_cfg {
    */
   unsigned int sframe_type;
 
+  /*!\brief sframe_replace_kf
+   *
+   * Number of consecutive keyframes to replace with S-frames between actual
+   * keyframes. 0: disabled, 1: K-S-K-S, 2: K-S-S-K-S-S, etc.
+   */
+  unsigned int sframe_replace_kf;
+
   /*!\brief Monochrome mode
    *
    * If this is nonzero, the encoder will generate a monochrome stream