vdec_create_chn

Applicability

Product	Supported (√/x)
Atlas A3 training products / Atlas A3 inference products	√
Atlas A2 training products / Atlas A2 inference products	√
Atlas training products	x
Atlas inference products	√
Atlas 200I/500 A2 inference products	√

Function Usage

Creates a decoding channel based on the configured channel attributes.

Prototype

C Prototype

        
             hi_s32 hi_mpi_vdec_create_chn(hi_vdec_chn chn, const hi_vdec_chn_attr *attr);

Python Function

        
             ret = acl.himpi.vdec_create_chn(chn, attr)

Parameter Description

Parameter	Description
chn	Int, decoding channel ID. Atlas inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256. Atlas A2 training products / Atlas A2 inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256. Among them, a maximum of 256 JPEGD decoding channels and 32 VDEC decoding channels are supported. Atlas 200I/500 A2 inference products : The value range of this parameter is [0, 128). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 128. Atlas A3 training products / Atlas A3 inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256. Among them, a maximum of 256 JPEGD decoding channels and 32 VDEC decoding channels are supported. NOTE: For Ascend virtual instances on the Atlas inference products : Total number of VDEC and JPEGD channels = (Total number of allocated VDEC and JPEGD hardware units/Total number of VDEC and JPEGD hardware units) x 256. If the total number of channels is not an integer, round down the value. For Ascend virtual instances on the Atlas A2 training products / Atlas A2 inference products : The number of VDEC channels = (Allocated VDEC hardware units/VDEC hardware units) x 32. If the total number of channels is not an integer, round down the value. The number of JPEGD channels is independent from the computing power, but the maximum number of JPEGD and VDEC channels is 256. For Ascend virtual instances on the Atlas 200I/500 A2 inference products : The number of VDEC channels = (Allocated VDEC hardware units/VDEC hardware units) x 128. If the total number of channels is not an integer, round down the value. The number of JPEGD channels is independent from the computing power, but the maximum number of JPEGD and VDEC channels is 128. You can run the npu-smi info -t template-info command on the server where Ascend AI Processor is installed to view the computing power specifications of the Ascend virtual instance in each scenario.
attr	Dict, dictionary of the decoding channel attributes. For details, see hi_vdec_chn_attr. If attr is left empty, the error code HI_ERR_VDEC_NULL_PTR is returned. When a setting in the channel attributes pointed by attr exceeds the decoding capability set, the error code HI_ERR_VDEC_ILLEGAL_PARAM is returned.

Parameter

Description

chn

Int, decoding channel ID.

Atlas inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256.
Atlas A2 training products / Atlas A2 inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256. Among them, a maximum of 256 JPEGD decoding channels and 32 VDEC decoding channels are supported.
Atlas 200I/500 A2 inference products : The value range of this parameter is [0, 128). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 128.
Atlas A3 training products / Atlas A3 inference products : The value range of this parameter is [0, 256). The JPEGD and VDEC functions share the same channels, and the maximum number of channels is 256. Among them, a maximum of 256 JPEGD decoding channels and 32 VDEC decoding channels are supported.

NOTE:

For Ascend virtual instances on the Atlas inference products : Total number of VDEC and JPEGD channels = (Total number of allocated VDEC and JPEGD hardware units/Total number of VDEC and JPEGD hardware units) x 256. If the total number of channels is not an integer, round down the value.

For Ascend virtual instances on the Atlas A2 training products / Atlas A2 inference products : The number of VDEC channels = (Allocated VDEC hardware units/VDEC hardware units) x 32. If the total number of channels is not an integer, round down the value. The number of JPEGD channels is independent from the computing power, but the maximum number of JPEGD and VDEC channels is 256.

For Ascend virtual instances on the Atlas 200I/500 A2 inference products : The number of VDEC channels = (Allocated VDEC hardware units/VDEC hardware units) x 128. If the total number of channels is not an integer, round down the value. The number of JPEGD channels is independent from the computing power, but the maximum number of JPEGD and VDEC channels is 128.

You can run the npu-smi info -t template-info command on the server where Ascend AI Processor is installed to view the computing power specifications of the Ascend virtual instance in each scenario.

attr

Dict, dictionary of the decoding channel attributes. For details, see hi_vdec_chn_attr.

If attr is left empty, the error code HI_ERR_VDEC_NULL_PTR is returned.
When a setting in the channel attributes pointed by attr exceeds the decoding capability set, the error code HI_ERR_VDEC_ILLEGAL_PARAM is returned.

Return Value Description

Return Value	Description
ret	Int, error code. 0: success. Other values: failures. For details, see Common Return Codes.

Restrictions

The channel ID of a single device cannot exceed the maximum channel ID.
Before this API call, ensure that a decoding channel has not been created yet or has been destroyed. Otherwise, a failure is returned.
If the OS memory is insufficient, the error code HI_ERR_VDEC_NO_MEM is returned. In this case, you can expand the OS memory as needed.
If the H.264 stream to be decoded has B-frames or the H.265 stream to be decoded supports temporal motion vector prediction (MVP) (sps_temporal_mvp_enabled_flag = 1), set temporal_mvp_en to 1 for the created channel and allocate video buffers (VBs) for the TMV output of each frame to avoid artifacts. The requested VB count of TMV output equals RefFrameNum plus 1. The TMV buffer size is much smaller than the image VB size, and can be queried by using the acl.himpi.vdec_get_tmv_buf_size call.
For H.264 and H.265 decoding, the minimum VB allocation per decoding channel is the sum of the number of reference frames and the number of display frames plus 1. For JPEG decoding, the minimum VB allocation per decoding channel is the number of display frames plus 1. The requested VB allocation varies according to the decode protocol and can be queried by using the acl.himpi.vdec_get_pic_buf_size call.
To skip decoding B-frames in H.264 streams or skip decoding H.265 streams with temporal MVP support (sps_temporal_mvp_enabled_flag = 1), set temporal_mvp_en to 0 for the created channel. In this case, no TMV information is output, and therefore you do not need to allocate a TMV VB pool, which saves memory.
Set the requested frame VB size (frame_buf_size) and count (frame_buf_cnt) as well as the requested TMV VB size (tmv_buf_size) based on the stream to be decoded. The decoder allocates private VB pools based on these configurations.
As long as the allocated frame buffer and TMV buffer are large enough, the decoding channel can decode a stream with any resolution in the valid range. The channel width and height are related only to the size of the stream buffer and SCD buffer.

Reference

For the API call sequence, see JPEGE and VENC.

Parent topic: VDEC/JPEGD APIs