Video Encoding Application

This chapter describes the GK7206 video encoding application example — sample_venc. The application demonstrates complete video encoding functionality, including H.265/H.264/MJPEG encoding, RTSP streaming, multiple rate control modes, QP Map, ROI, JPEG snapshots, and other advanced features.

The application source code is located in the SDK directory sample/venc/. It serves as a reference template for developing video encoding and streaming applications.

Important note (updated 2026-07-24)

The sample_venc source code has been modified so that all save paths changed from "." to "/sd_card" (8 places in total). It now writes to /sd_card directly no matter which directory it is run from — no cd /sd_card needed. The prerequisite is that the SD card is mounted at /sd_card.

1 Application Overview

1.1 Features

  • Multiple encoding formats: H.265, H.264, MJPEG, JPEG
  • Multiple stream modes: main stream + sub stream, MJPEG stream + JPEG snapshot
  • Multiple rate control modes: CBR, VBR, AVBR, FixQP
  • RTSP streaming: built-in RTSP server for real-time stream pushing
  • Advanced encoding features:
    • QP Map (quantization parameter map)
    • ROI (region of interest encoding)
    • Ring-buffer low-latency encoding
    • JPEG snapshot split-and-zoom encoding
  • File encoding: supports encoding a YUV file into a stream file
  • Automatic save path: all output files are saved to /sd_card automatically

1.2 Technical Specifications

ParameterValue
Encoding formatsH.265, H.264, MJPEG, JPEG
ResolutionPer the sensor configuration (e.g. 2560×1440)
Frame rateDetermined by the sensor (usually 30 FPS)
Rate control modesCBR, VBR, AVBR, FixQP
GOP modesNORMALP, SMARTP
RTSP port554
Output path/sd_card (hard-coded in the source)
Memory footprintRelatively high (requires a sensor)

1.3 Test Case List

indexNameTest commandExpected behavior (success)Possible failure cause
0Low-latency ring buffer./sample_venc 0Prints rtsp://<ip>:554/livestream/0, .../1; any key other than q captures a pictureOutput written to /tmp → Killed (OOM)
1Main + sub stream./sample_venc 1Same dual RTSP streams as aboveSame as above
2qpmap./sample_venc 2qpmap encoding over RTSPsensor/VB failure
3roi./sample_venc 3roi encoding over RTSPSame as above
4mjpeg+snap./sample_venc 4MJPEG stream + key-triggered JPEG captureSame as above
5snap zoom./sample_venc 5snap split-and-zoom encodingSame as above
FileYUV→stream./sample_venc /sd_card/in.yuv 1920 1080 h264Generates an encoded stream fileWrong YUV file/format

1.4 Directory Structure

sample/venc/
├── Makefile              # Build script
└── sample_venc.c         # Main program

2 Build and Deployment

2.1 Prerequisites

Before building this application, make sure the following preparations have been completed:

  1. SDK environment is set up: follow SDK Compilation to set up the cross-compilation toolchain and SDK configuration
  2. Sensor is connected: an SC465SL or compatible image sensor must be connected

2.2 Build the Application

# Enter the sample directory
cd <SDK_PATH>/sample

# Build the venc sample
make -C venc clean && make -C venc

Or build from the top level:

make -C sample all

2.3 Deploy to the Board

# Mount the SD card
mkdir -p /sd_card
mount -t vfat /dev/mmcblk1p1 /sd_card

# Transfer to the development board via SCP
scp sample/venc/sample_venc root@<board IP>:/sd_card/

# Or download via TFTP
tftp -g -r sample_venc <board IP>

Warning

The SD card must be mounted at /sd_card, otherwise the program cannot save the captured pictures.

2.4 Run the Application

# Add execute permission
chmod +x /sd_card/sample_venc

# Run (index 0: low-latency ring buffer)
./sample_venc 0

# Interactively select the rate control mode
c  # Select CBR

# Interactively select the GOP mode
0  # Select NORMALP

2.5 Expected Output

Index 0: Low-latency ring buffer

Startup flow:

please input choose rc mode!
         c) cbr.
         v) vbr.
         a) avbr.
         f) fixQp
c
please input choose gop mode!
         0) NORMALP.
         1) SMARTP.
0
[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================

rtsp://192.168.49.17:554/livestream/0
rtsp://192.168.49.17:554/livestream/1
[venc] save path = /sd_card (orig '.', readonly rootfs)
---press 'q' to exit or any other key to capture pic---
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Interactive selection of the rate control mode:

please input choose rc mode!
	 c) cbr.
	 v) vbr.
	 a) avbr.
	 f) fixQp
c

Interactive selection of the GOP mode:

please input choose gop mode!
	 0) NORMALP
	 1) SMARTP
0

Success indicators:

  • The RTSP addresses are displayed: rtsp://<ip>:554/livestream/0 and livestream/1
  • [venc] save path = /sd_card indicates the save path is correct
  • The sensor initialized successfully: SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success!
  • The interactive prompt ---press 'q' to exit or any other key to capture pic--- is displayed

Fixed and variable parts

  • Fixed parts: the sensor model (SC465SL), resolution (2560x1440), frame rates (25/30 fps), MIPI rate (864), and save path hint
  • Variable parts: the IP address in the RTSP URLs (varies with the board's network configuration)

Index 1: Main + sub stream

Expected output:

please input choose rc mode!
         c) cbr.
         v) vbr.
         a) avbr.
         f) fixQp
c
please input choose gop mode!
         0) NORMALP.
         1) SMARTP.
0
[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================

rtsp://192.168.49.17:554/livestream/0
rtsp://192.168.49.17:554/livestream/1
[venc] save path = /sd_card (orig '.', readonly rootfs)
---------------press any key to exit!---------------
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Success indicator: two RTSP stream addresses are displayed — the main stream (0) and the sub stream (1).

Fixed and variable parts

  • Fixed parts: the sensor model, resolution, frame rates, MIPI rate, and save path hint
  • Variable parts: the IP address in the RTSP URLs, and the interactive prompt (---press 'q' to exit vs ---------------press any key to exit!---------------)

Index 2: qpmap

Expected output:

please input choose gop mode!
         0) NORMALP.
         1) SMARTP.
0
[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================

rtsp://192.168.49.17:554/livestream/0
rtsp://192.168.49.17:554/livestream/1
[venc] save path = /sd_card (orig '.', readonly rootfs)
---------------press any key to exit!---------------
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Success indicator: qpmap initializes successfully and the RTSP addresses are displayed.

Fixed and variable parts

  • Fixed parts: the sensor model, resolution, frame rates, MIPI rate, and save path hint
  • Variable parts: the IP address in the RTSP URLs

Index 3: roi

Expected output:

please input choose rc mode!
         c) cbr.
         v) vbr.
         a) avbr.
         f) fixQp
c
please input choose gop mode!
         0) NORMALP.
         1) SMARTP.
0
[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================

rtsp://192.168.49.17:554/livestream/0
rtsp://192.168.49.17:554/livestream/1
[venc] save path = /sd_card (orig '.', readonly rootfs)
---------------press any key to exit!---------------
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Success indicator: roi initializes successfully and the RTSP addresses are displayed.

Fixed and variable parts

  • Fixed parts: the sensor model, resolution, frame rates, MIPI rate, and save path hint
  • Variable parts: the IP address in the RTSP URLs

Index 4: mjpeg+snap

Expected output:

please input choose rc mode!
         c) cbr.
         v) vbr.
         a) avbr.
         f) fixQp
c
[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================
[venc] save path = /sd_card (orig '.', readonly rootfs)
---press 'q' to exit or any other key to capture pic---
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Success indicator: the MJPEG stream address is displayed and JPEG pictures can be captured by pressing keys.

Fixed and variable parts

  • Fixed parts: the sensor model, resolution, frame rates, MIPI rate, and save path hint
  • Variable parts: no RTSP URL (this mode does not output an RTSP stream)

Index 5: snap zoom

Expected output:

[SENSOR][Func]:sc465sl_set_slave_addr [Line]:1637 [Info]:Sensor dev [0] set slave addr 0x60 success.
[SENSOR][Func]:sc465sl_i2c_init [Line]:1664 [Info]:====== i2c[1] init success!=======
[SENSOR][Func]:sc465sl_set_wdr_mode [Line]:487 [Info]:linear mode
[sample_comm_isp_sensor_init]-368: sensor i2c_id = 1, clk_id = 1
[SENSOR][Func]:sc465sl_get_ae_common_default [Line]:858 [Info]:man_ratio_enable: 0
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 30.000000
[ISP]isp_init[1113]: isp[0] init success
[ISP]isp_run[771]: isp run.
[sample_comm_vi_start_dev]-1066: mipi_rate: 864.
[ISP]isp_start[503]: isp0 start.
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:952 [Info]:============================================================================
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:953 [Info]:=== SC465SL_27MInput_MIPI_4lane_12bit_30fps_2560x1440_linear init success! =
[SENSOR][Func]:sc465sl_4lane_linear_2560x1440_init [Line]:954 [Info]:============================================================================
---press 'q' to exit or any other key to capture pic---
[SENSOR][Func]:sc465sl_calc_fps [Line]:1358 [Info]:sc465sl set fps = 25.000000
^C[ISP]isp_stop[522]: isp0 stop.
[ISP]isp_exit[1183]: isp0 start exit
[ISP]isp_exit[1218]: isp0 exit success
[main]-1772: program exit normally!

Success indicator: the snap split-and-zoom encoding information and the RTSP addresses are displayed.

Fixed and variable parts

  • Fixed parts: the sensor model, resolution, frame rates, MIPI rate, and interactive prompt
  • Variable parts: no RTSP URL (this mode does not output an RTSP stream)

File encoding mode

Command: ./sample_venc /sd_card/in.yuv 1920 1080 h264

Expected output:

sample_venc file encode running
input file: /sd_card/in.yuv
width: 1920
height: 1080
codec: h264
...
encode completed, output: /sd_card/in.264

Success indicator: an encoded stream file is generated, such as in.264, in.265, or in.mjpg.

Error cases

open file[./chn2_snap_0.jpg] err!

Cause: the SD card is not mounted or the path is wrong Solution: confirm the SD card is mounted at /sd_card

Killed

Cause: out of memory (OOM); the output was written to the /tmp memory disk Solution: confirm the SD card is mounted and check that /sd_card is writable

2.6 Access from a Browser/Player

Use VLC or ffplay to pull the stream:

# Pull the main stream
ffplay rtsp://<board IP>:554/livestream/0

# Pull the sub stream
ffplay rtsp://<board IP>:554/livestream/1

3 Internal Execution Logic in Detail

3.1 Application Architecture

The application uses the following architecture:

Sensor → VI → VPSS → VENC → RTSP streaming
                  ↓
                 MJPEG stream
                  ↓
               JPEG snapshot

3.2 Video Pipeline Initialization Flow

// Step 1: System initialization (configures the VB memory pool)
sample_comm_sys_init(&sys_config);

// Step 2: ISP initialization
sample_comm_isp_init();

// Step 3: Start VI
sample_comm_vi_start(...);

// Step 4: Start VPSS
sample_comm_vpss_start(...);

// Step 5: Start VENC
sample_comm_venc_start(...);

// Step 6: Bind the modules
xmedia_bind_vi_to_vpss(...);
xmedia_bind_vpss_to_venc(...);

// Step 7: RTSP streaming
sample_comm_livestream_create(...);

3.3 RTSP Streaming Implementation

RTSP streaming uses the built-in live_rtsp_server library:

// Create an RTSP session
sample_comm_livestream_create(venc_chn, livestream_type);

// Start the RTSP service
sample_comm_livestream_start();

3.4 Snapshot Function

The snapshot function is triggered by key presses:

// Wait for user input
c = getchar();

if (c != 'q') {
    // Generate a JPEG snapshot
    sample_venc_snap_process(venc_chn, snap_cnt);

    // Print the save path
    printf("[venc] save path = /sd_card/chn2_snap_%d.jpg\n", snap_cnt);
}

3.5 Source Code Changes (2026-07-24)

8 save paths in the source changed from "." to "/sd_card":

// Original code (line comment kept)
// snprintf(snap_path, sizeof(snap_path), "./chn%d_snap_%d.jpg", chn, cnt);

// New code
snprintf(snap_path, sizeof(snap_path), "/sd_card/chn%d_snap_%d.jpg", chn, cnt);
printf("[venc] save path = %s\n", snap_path);

Where the changes are located:

  • start_get_stream() function: 5 places
  • capture_jpeg() function: 2 places
  • splicing function: 1 place

4 Key Programming Points

4.1 Selecting the Rate Control Mode

The application provides interactive selection of the rate control mode:

sample_rc sample_venc_get_rc_mode(void)
{
    char c;
    printf("please input choose rc mode!\n");
    printf("\t c) cbr.\n");
    printf("\t v) vbr.\n");
    printf("\t a) avbr.\n");
    printf("\t f) fixQp\n");

    c = getchar();
    switch(c) {
        case 'c': return SAMPLE_RC_CBR;
        case 'v': return SAMPLE_RC_VBR;
        case 'a': return SAMPLE_RC_AVBR;
        case 'f': return SAMPLE_RC_FIXQP;
        default:  goto begin_get;
    }
}

4.2 Encoding Channel Configuration

// H.265 main stream
venc_chn_attr[0].type = XMEDIA_PT_H265;
venc_chn_attr[0].max_width = 2560;
venc_chn_attr[0].max_height = 1440;
venc_chn_attr[0].rc_mode = VENC_RC_MODE_H265CBR;

// H.264 sub stream
venc_chn_attr[1].type = XMEDIA_PT_H264;
venc_chn_attr[1].max_width = 640;
venc_chn_attr[1].max_height = 480;
venc_chn_attr[1].rc_mode = VENC_RC_MODE_H264CBR;

// JPEG snapshot
venc_chn_attr[2].type = XMEDIA_PT_JPEG;
venc_chn_attr[2].max_width = 2560;
venc_chn_attr[2].max_height = 1440;

4.3 Error Handling

Check the return value of every API call:

ret = sample_comm_sys_init(&sys_config);
if (ret != XMEDIA_SUCCESS) {
    printf("sys init failed!\n");
    goto exit0;
}

ret = sample_comm_isp_init();
if (ret != XMEDIA_SUCCESS) {
    printf("isp init failed!\n");
    goto exit1;
}

5 Troubleshooting

ProblemPossible causeSolution
Killed (OOM)Output written to the /tmp memory diskConfirm the SD card is mounted at /sd_card
open file[./chn2_snap_0.jpg] err!Old source with the "." path on a read-only rootfsUpdate to the new source and rebuild
Cannot pull the RTSP streamSensor initialization failedCheck the sensor connection and configuration
Encoding failureInsufficient VB memoryAdjust the VB pool configuration
Snapshot failureJPEG channel not configuredCheck the VENC channel configuration

6 Memory and Path Management

6.1 Memory Limits

The board has 128 MB of DDR in total, of which about 26 MB is available to Linux. Video encoding uses a lot of memory, so it is recommended to:

  1. Mount the SD card at /sd_card
  2. Write all output files to the SD card
  3. Free memory before testing: sync; echo 3 > /proc/sys/vm/drop_caches

6.2 Path Management

Tips

The save path is hard-coded to /sd_card in the source, so there is no need to cd /sd_card. But the SD card must be mounted first.

7 References