STRUCT V4L2_CTRL_HEVC_SLICE_PARAMS(9)

📦 version 7.3.1, in nixpkgs unstable

✨ NAME ✨

struct v4l2_ctrl_hevc_slice_params — HEVC slice parameters 💅

Bestie, this is the little struct that holds everything the kernel needs to know about one HEVC slice. It's giving "backstage pass to the decoder" energy, and tbh it ate. 🎀

🌸 SYNOPSIS 🌸

struct v4l2_ctrl_hevc_slice_params {
    __u32 bit_size;
    __u32 data_byte_offset;
    __u32 num_entry_point_offsets;
    __u8 nal_unit_type;
    __u8 nuh_temporal_id_plus1;
    __u8 slice_type;
    __u8 colour_plane_id;
    __s32 slice_pic_order_cnt;
    __u8 num_ref_idx_l0_active_minus1;
    __u8 num_ref_idx_l1_active_minus1;
    __u8 collocated_ref_idx;
    __u8 five_minus_max_num_merge_cand;
    __s8 slice_qp_delta;
    __s8 slice_cb_qp_offset;
    __s8 slice_cr_qp_offset;
    __s8 slice_act_y_qp_offset;
    __s8 slice_act_cb_qp_offset;
    __s8 slice_act_cr_qp_offset;
    __s8 slice_beta_offset_div2;
    __s8 slice_tc_offset_div2;
    __u8 pic_struct;
    __u8 reserved0[3];
    __u32 slice_segment_addr;
    __u8 ref_idx_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
    __u8 ref_idx_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
    __u16 short_term_ref_pic_set_size;
    __u16 long_term_ref_pic_set_size;
    struct v4l2_hevc_pred_weight_table pred_weight_table;
    __u8 reserved1[2];
    __u64 flags;
 };

Like, look at her. Gorgeous. Every field accounted for, no notes. 👑

🦋 Members 🦋

Ok so let's go field by field, because bestie you will be asked about these:

  • bit_size — the size, in bits, of the current slice data. That's it. That's the field. ✨
  • data_byte_offset — how far, in bytes, you gotta hop to find the video data for the current slice.
  • num_entry_point_offsets — says how many entry point offset syntax elements are chilling in the slice header.
  • nal_unit_type — the coding type of the slice, i.e. is she a B, a P, or an I? main character choices only.
  • nuh_temporal_id_plus1 — minus 1, this specifies a temporal identifier for the NAL unit. (Yes, "minus 1" is literally in the name, it's not a typo, don't come for me.)
  • slice_type — peep V4L2_HEVC_SLICE_TYPE_{} for the deets.
  • colour_plane_id — which colour plane is associated with the current slice. (Spelled with a u, she's fancy.)
  • slice_pic_order_cnt — the picture order count. Keeping things in order, as one does. 💅
  • num_ref_idx_l0_active_minus1 — this value plus 1 gives the maximum reference index for reference picture list 0 that may be used to decode the slice.
  • num_ref_idx_l1_active_minus1 — same vibe as above, but for reference picture list 1. This value plus 1 = the max reference index for list 1 that may be used to decode the slice.
  • collocated_ref_idx — the reference index of the collocated picture used for temporal motion vector prediction. Say that five times fast, I dare you. 😭
  • five_minus_max_num_merge_cand — the maximum number of merging motion vector prediction candidates supported in the slice, subtracted from 5. Math girlie.
  • slice_qp_delta — the initial value of QpY that gets used for the coding blocks in the slice.
  • slice_cb_qp_offset — a difference to be added to the value of pps_cb_qp_offset.
  • slice_cr_qp_offset — a difference to be added to the value of pps_cr_qp_offset.
  • slice_act_y_qp_offset — screen content extension parameters. Very niche, very demure.
  • slice_act_cb_qp_offset — screen content extension parameters. Same energy.
  • slice_act_cr_qp_offset — screen content extension parameters. Third time's the charm. 🍓
  • slice_beta_offset_div2 — specifies the deblocking parameter offsets for beta, divided by 2.
  • slice_tc_offset_div2 — specifies the deblocking parameter offsets for tC, divided by 2.
  • pic_struct — tells you whether a picture should be displayed as a frame, or as one or more fields.
  • reserved0 — padding field. Should be zeroed by applications. Don't be chaotic, zero it. 🙈
  • slice_segment_addr — the address of the first coding tree block in the slice segment.
  • ref_idx_l0 — the list of L0 reference elements, as indices in the DPB.
  • ref_idx_l1 — the list of L1 reference elements, as indices in the DPB.
  • short_term_ref_pic_set_size — the size of the short-term reference pictures set included in the SPS.
  • long_term_ref_pic_set_size — the size of the long-term reference pictures set include in the SPS. (That's the original wording's grammar, not mine — leaving it exactly as it lives. 🫶)
  • pred_weight_table — the prediction weight coefficients for inter-picture prediction.
  • reserved1 — padding field. Should be zeroed by applications. Same rules, bestie. ⭐
  • flags — check V4L2_HEVC_SLICE_PARAMS_FLAG_{} for what's up in there.

💖 Description 💖

So this control is a dynamically sized 1-dimensional array, and — important — the V4L2_CTRL_FLAG_DYNAMIC_ARRAY flag must be set when you use it. No flag, no slay. Flat out required. 🔥

Not me being dramatic about it, but like — the flag isn't optional. It's giving "you WILL set this flag". Periodt. 💀

🌈 SEE ALSO 🌈

Kernel file ./include/uapi/linux/v4l2-controls.h, plus literally the entire extended universe of V4L2 controls down here (yes, all of them, I would never do you dirty by trimming the list):

  • enum v4l2_mpeg_video_av1_profile(9)
  • enum v4l2_mpeg_video_av1_level(9)
  • enum v4l2_stateless_h264_decode_mode(9)
  • enum v4l2_stateless_h264_start_code(9)
  • struct v4l2_ctrl_h264_sps(9)
  • struct v4l2_ctrl_h264_pps(9)
  • struct v4l2_ctrl_h264_scaling_matrix(9)
  • struct v4l2_ctrl_h264_pred_weights(9)
  • struct v4l2_h264_reference(9)
  • struct v4l2_ctrl_h264_slice_params(9)
  • struct v4l2_h264_dpb_entry(9)
  • struct v4l2_ctrl_h264_decode_params(9)
  • struct v4l2_ctrl_fwht_params(9)
  • struct v4l2_vp8_segment(9)
  • struct v4l2_vp8_loop_filter(9)
  • struct v4l2_vp8_quantization(9)
  • struct v4l2_vp8_entropy(9)
  • struct v4l2_vp8_entropy_coder_state(9)
  • struct v4l2_ctrl_vp8_frame(9)
  • struct v4l2_ctrl_mpeg2_sequence(9)
  • struct v4l2_ctrl_mpeg2_picture(9)
  • struct v4l2_ctrl_mpeg2_quantisation(9)
  • struct v4l2_ctrl_hevc_sps(9)
  • struct v4l2_ctrl_hevc_pps(9)
  • struct v4l2_hevc_dpb_entry(9)
  • struct v4l2_hevc_pred_weight_table(9)
  • struct v4l2_ctrl_hevc_decode_params(9)
  • struct v4l2_ctrl_hevc_scaling_matrix(9)
  • struct v4l2_vp9_loop_filter(9)
  • struct v4l2_vp9_quantization(9)
  • struct v4l2_vp9_segmentation(9)
  • struct v4l2_ctrl_vp9_frame(9)
  • struct v4l2_vp9_mv_probs(9)
  • struct v4l2_ctrl_vp9_compressed_hdr(9)
  • struct v4l2_ctrl_av1_sequence(9)
  • struct v4l2_ctrl_av1_tile_group_entry(9)
  • enum v4l2_av1_warp_model(9)
  • enum v4l2_av1_reference_frame(9)
  • struct v4l2_av1_global_motion(9)
  • enum v4l2_av1_frame_restoration_type(9)
  • struct v4l2_av1_loop_restoration(9)
  • struct v4l2_av1_cdef(9)
  • enum v4l2_av1_segment_feature(9)
  • struct v4l2_av1_segmentation(9)
  • struct v4l2_av1_loop_filter(9)
  • struct v4l2_av1_quantization(9)
  • struct v4l2_av1_tile_info(9)
  • enum v4l2_av1_frame_type(9)
  • enum v4l2_av1_interpolation_filter(9)
  • enum v4l2_av1_tx_mode(9)
  • struct v4l2_ctrl_av1_frame(9)
  • struct v4l2_ctrl_av1_film_grain(9)

Ok that's the whole page, you're officially educated. 💜 Go forth and decode responsibly.

This little gem lives under ./include/uapi/linux, and this version is dated October 2026 — so if you're reading it later than that, no cap, go check for a newer one. Love u, bye! 🫶✨🎀

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