vp9 encoder returns a null packet - c++

Question

i using this code to encode video stream using vp8 and i decided to give vp9 a try so i changed every thing with starts with vp_* from 8 to 9.
but the vp9 encoder always return a null packet although the encoder doesn't return any error.
here is the code i'am using for configuring.
vpx_codec_err_t error = vpx_codec_enc_config_default(vpx_codec_vp9_cx(), &enc_cfg, 0);
if(error != VPX_CODEC_OK)
return error;
enc_cfg.g_timebase.den = fps;
enc_cfg.rc_undershoot_pct = 95;
enc_cfg.rc_target_bitrate = bitrate;
enc_cfg.g_error_resilient = 1;
enc_cfg.kf_max_dist = 999999;
enc_cfg.rc_buf_initial_sz = 4000;
enc_cfg.rc_buf_sz = 6000;
enc_cfg.rc_buf_optimal_sz = 5000;
enc_cfg.rc_end_usage = VPX_CBR;
enc_cfg.g_h = height;
enc_cfg.g_w = width;
enc_cfg.rc_min_quantizer = 4;
enc_cfg.rc_max_quantizer = 56;
enc_cfg.g_threads = 4;
enc_cfg.g_pass = VPX_RC_ONE_PASS;
error = vpx_codec_enc_init(&codec, vpx_codec_vp9_cx(), &enc_cfg, 0);
if(error != VPX_CODEC_OK)
return error;
vpx_img_alloc(&vpx_image,VPX_IMG_FMT_I420 , width, height, 1);
configured = true;
return VPX_CODEC_OK;
and the code for the encoding
libyuv::RAWToI420(frame, vpx_image.d_w * 3, vpx_image.planes[VPX_PLANE_Y],vpx_image.stride[VPX_PLANE_Y],
vpx_image.planes[VPX_PLANE_U], vpx_image.stride[VPX_PLANE_U], vpx_image.planes[VPX_PLANE_V],
vpx_image.stride[VPX_PLANE_V], vpx_image.d_w, vpx_image.d_h);
const vpx_codec_cx_pkt_t *pkt;
vpx_codec_err_t error = vpx_codec_encode(&codec, &vpx_image, 0, 1, 0, VPX_DL_GOOD_QUALITY);
if(error != VPX_CODEC_OK)
return vector<byte>();
vpx_codec_iter_t iter = NULL;
if((pkt = vpx_codec_get_cx_data(&codec, &iter)))//always return null ?
{
if(pkt->kind == VPX_CODEC_CX_FRAME_PKT)
{
int length = pkt->data.frame.sz;
byte* buf = (byte*) pkt->data.frame.buf;
vector<byte> data(buf, buf + length);
return data;
}
return vector<byte>();
}
return vector<byte>();
the code is fully working if i'am using vp8 instead of 9, any help is welcomed

Answer 1

Just came across this post because I faced the same problem. Just for other to know: I solved it with setting
enc_cfg.g_lag_in_frames = 0;
This basically disallows the encoder to consume up to default 25 frames until it produces any output.