VENC

API Call Sequence

Figure 1 Process of calling the VENC video encoding function

Optimization of Video Encoding Quality

When implementing the VENC function, you can set basic parameters during channel creation or set advanced parameters by calling the corresponding set API to optimize the video encoding quality. The following optimization settings are available and can be used jointly:

• Settings for H.264 monitoring with the resolution of 720p, GOP of 60, frame rate of 30 FPS, and bit rate of 1 Mbit/s: CBR mode, HI_VENC_SCENE_0, stats_time = 2, profile = 2, and macroblock-level bit rate control = disabled.
• Settings for H.265 movies with the resolution of 1080p, GOP of 30, frame rate of 25 FPS, and bit rate of 2 Mbit/s: CBR mode, HI_VENC_SCENE_1, stats_time = 1, and macroblock-level bit rate control = disabled.

You can optimize the video encoding quality using the following methods:

• Setting basic parameters for overall quality optimization

  The encoding quality of videos with different resolutions is related to the video frame rate, GOP, and bit rate. When a channel is created by calling hi_mpi_venc_create_chn, you can set the encoding profile and parameters such as the frame rate, GOP, and bit rate in CBR/VBR/AVBR/CVBR/QVBR mode for H.264/H.265 encoding to optimize the video encoding quality.

  • Encoding profile, which is specified by the profile parameter in the hi_venc_chn_attr.venc_attr struct.
  • Frame rate, which is specified by the src_frame_rate and dst_frame_rate parameters in the hi_venc_chn_attr.rc_attr struct.
  • GOP, which is specified by the gop parameter in the hi_venc_chn_attr.rc_attr struct.
  • Bit rate, which is specified by the bit_rate, max_bit_rate, or target_bit_rate parameters in the hi_venc_chn_attr.rc_attr struct.

  Table 1 Values of the frame rate, GOP, and bit rate in typical scenarios

  Picture Quality/Resolution	Frame Rate (FPS)	GOP	Bit Rate (Mbit/s)
  4K 3840 x 2160/4096 x 2160	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 8 to 12 for H.264/H.265 streams Show/Livestreaming/Short video 6 to 12 for H.265 streams N/A for H.264 streams Game video 10 to 16 for H.264/H.265 streams
  2K 2560 x 1440	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 6 to 10 for H.264/H.265 streams Show/Livestreaming/Short video 4.8 to 8 for H.265 streams N/A for H.264 streams Game video 6 to 10 for H.264/H.265 streams
  1080p (Blu-ray) 1920 x 1080	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 1 to 4 for H.265 streams 2 to 6 for H.264 streams Show/Livestreaming/Short video 1.4 to 3.6 for H.265 streams 2 to 4.8 for H.264 streams Game video 3 to 6 for H.264/H.265 streams
  720p (HD) 1280 x 720	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 0.8 to 2 for H.265 streams 1 to 3 for H.264 streams Show/Livestreaming/Short video 1 to 2 for H.265 streams 1 to 3 for H.264 streams Game video 2 to 4 for H.264/H.265 streams
  480p/D1_N (SD) 854 x 480/720 x 480	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 0.3 to 0.7 for H.265 streams 0.6 to 1.4 for H.264 streams Show/Livestreaming/Short video 0.25 to 0.6 for H.265 streams 0.3 to 0.7 for H.264 streams Game video N/A
  576p/D1 (SD) 720 x 576	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 0.3 to 0.7 for H.265 streams 0.6 to 1.4 for H.264 streams Show/Livestreaming/Short video 0.25 to 0.6 for H.265 streams 0.3 to 0.7 for H.264 streams Game video N/A
  270p (smooth) 480 x 270	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining N/A Show/Livestreaming/Short video 0.2 for H.265 streams 0.3 for H.264 streams Game video N/A
  CIF P/N 352 x 288/320 x 240	25 or 30	It is recommended that the GOP value be an integral multiple of the frame rate. For example, if the frame rate is 25, the recommended GOP value is 25 or 50.	Video data obtaining 0.25 for H.264/H.265 streams Show/Livestreaming/Short video N/A Game video N/A

• Setting advanced parameters for quality tuning

  You can call the APIs listed in the following table to set the bit rate control mode, macroblock-level bit rate control parameters, and encoding scene mode to tune video encoding quality.

  Table 2 Advanced settings

  Item	API	Parameter	Description
  Bit rate control mode	hi_mpi_venc_create_chn	rc_mode in the hi_venc_chn_attr.rc_attr struct	Set this parameter to CBR if a stable bit rate or a large peak signal to noise ratio (PSNR) and qualified bit rate is required. Set this parameter to VBR to save the bit rate and improve the subjective quality of encoding. Set this parameter to AVBR to save the bit rate and improve the subjective quality of encoding with lots of still images in the scene. Set this parameter to QVBR if a large PSNR is required and there is no strict requirement on the bit rate increase. Set this parameter to CVBR to save the bit rate and improve the subjective quality of encoding when the bandwidth and storage space can also be used for optimization.
  Statistical time of the bit rate control model	hi_mpi_venc_create_chn	stats_time in the hi_venc_chn_attr.rc_attr struct	Set this parameter to a large value in the scenario where long-term bit rate stability is required without considering short-term fluctuations, for example, DVR storage. This setting increases the threshold for re-encoding to cut the number of re-encoding times, but also increases bit rate fluctuations at the same time.
  Macroblock-level bit rate control	hi_mpi_venc_set_rc_param	threshold_i, threshold_p, threshold_b, direction, and row_qp_delta in the hi_venc_rc_param struct	Disable this function when encoding complex images with rich details, or when objective indicators such as the PSNR are concerned.
  Start QP value of the first frame	hi_mpi_venc_create_chn	first_frame_start_qp in the hi_venc_rc_param struct	In typical scenarios, if the configured bit rate is less than the reference value provided in Table 1 and the first frame of the encoded video is blurry, you are advised to set first_frame_start_qp to the middle value of [min_i_qp, max_i_qp]. For example, if [min_i_qp, max_i_qp] is [30, 40], set first_frame_start_qp to 35. In addition, set max_reencode_times to 0.
  Encoding scene mode	hi_mpi_venc_set_scene_mode	hi_venc_scene_mode	Set this parameter to HI_VENC_SCENE_0 for security scenes. Set this parameter to HI_VENC_SCENE_1 for assisted driving, livestreaming, gaming, animations, and movies.

Sample Code

The following is a code snippet of key steps for VENC video encoding. It is for reference only. Do not copy, build, or run it directly. After APIs are called, you need to add exception handling branches and record error logs and info logs.

You can click venc_sample to obtain the sample.

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// 1. Initialize the media data processing system.
int32_t ret = hi_mpi_sys_init();

// 2. Create a channel.
hi_venc_chn chn = 0;
hi_venc_chn_attr attr{};
attr.venc_attr.type = HI_PT_H265;
attr.venc_attr.profile = 0;
attr.venc_attr.max_pic_width = 128;
attr.venc_attr.max_pic_height = 128;
attr.venc_attr.pic_width = 128;
attr.venc_attr.pic_height = 128;
attr.venc_attr.buf_size = 2 * 1024 * 1024;
attr.venc_attr.is_by_frame = HI_TRUE;
attr.rc_attr.rc_mode = HI_VENC_RC_MODE_H265_VBR;
attr.rc_attr.h265_vbr.gop = 30;
attr.rc_attr.h265_vbr.stats_time = 1;
attr.rc_attr.h265_vbr.src_frame_rate = 30;
attr.rc_attr.h265_vbr.dst_frame_rate = 30;
attr.rc_attr.h265_vbr.max_bit_rate = 4000;
attr.gop_attr.gop_mode = HI_VENC_GOP_MODE_NORMAL_P;
attr.gop_attr.normal_p.ip_qp_delta = 3;
ret = hi_mpi_venc_create_chn(chn, &attr);

// 3. Notify the encoder to start receiving input data.
hi_venc_start_param recv_param{};
recv_param.recv_pic_num = -1;
ret = hi_mpi_venc_start_chn(chn, &recv_param);

// 4. Send the input data.
// 4.1 Allocate input buffer.
uint8_t* inputAddr = nullptr;
int32_t inputSize = 128 * 128 * 3 / 2;
ret = hi_mpi_dvpp_malloc(0, &inputAddr, inputSize);

// Load the input data into the device buffer. The function VencReadYuvFile is implemented by the user.
VencReadYuvFile(streamName, inputAddr, inputSize);

// 4.2 Send the input data and start encoding.
hi_video_frame_info frame{};
frame.mod_id = HI_ID_VENC;
frame.v_frame.width = 128;
frame.v_frame.height = 128;
frame.v_frame.field = HI_VIDEO_FIELD_FRAME;
frame.v_frame.pixel_format = HI_PIXEL_FORMAT_YUV_SEMIPLANAR_420;
frame.v_frame.video_format = HI_VIDEO_FORMAT_LINEAR;
frame.v_frame.compress_mode = HI_COMPRESS_MODE_NONE;
frame.v_frame.dynamic_range = HI_DYNAMIC_RANGE_SDR8;
frame.v_frame.color_gamut = HI_COLOR_GAMUT_BT709;
frame.v_frame.width_stride[0] = 128;
frame.v_frame.width_stride[1] = 128;
frame.v_frame.width_stride[2] = 128;
frame.v_frame.virt_addr[0] = inputAddr;
frame.v_frame.virt_addr[1] = (hi_void *)((uintptr_t)frame.v_frame.virt_addr[0] + 128 * 128);
frame.v_frame.frame_flag = 0;
frame.v_frame.time_ref = 0;
frame.v_frame.pts = 0;
ret = hi_mpi_venc_send_frame(chn, &frame, 0);

// 5. Obtain the encoding result.
//5.1 Create an epoll instance.
int32_t epollFd = 0;
int32_t fd = hi_mpi_venc_get_fd(chn);
ret = hi_mpi_sys_create_epoll(10, &epollFd);

hi_dvpp_epoll_event event;
event.events = HI_DVPP_EPOLL_IN;
event.data = (void*)(unsigned long)(fd);
ret = hi_mpi_sys_ctl_epoll(epollFd, HI_DVPP_EPOLL_CTL_ADD, fd, &event);

int32_t eventCount = 0;
// Before the encoding is complete, timeout occurs. The next step is not performed until the encoding is complete.
ret = hi_mpi_sys_wait_epoll(epollFd, events, 3, 1000, &eventCount);

// 5.2 Obtain the encoding result.
hi_venc_chn_status stat;
ret = hi_mpi_venc_query_status(chn, &stat);
hi_venc_stream stream;
stream.pack_cnt = stat.cur_packs;
stream.pack = new hi_venc_pack[stream.pack_cnt];
ret = hi_mpi_venc_get_stream(chn, &stream, 1000);

// 5.3 Obtain the encoded streams.
// You can directly use the encoded streams, which are stored in the buffer specified by stream.pack[0].addr.
// TODO: inference-related code logic

// 6. Free the input buffer and release the output streams.
ret = hi_mpi_dvpp_free(inputAddr);
ret = hi_mpi_venc_release_stream(chn, &stream);
delete[] stream.pack;

// 7. Notify the encoder to stop receiving input data.
ret = hi_mpi_venc_stop_chn(chn);
ret = hi_mpi_sys_ctl_epoll(epollFd, HI_DVPP_EPOLL_CTL_DEL, fd, NULL);
ret = hi_mpi_sys_close_epoll(epollFd);

// 8. Destroy the channel.
ret = hi_mpi_venc_destroy_chn(chn);

// 9. Deinitialize the media data processing system.
ret = hi_mpi_sys_exit();

// ....