NVIDIA GPUs - beginning with the Kepler generation - contain a hardware-based encoder (referred to as NVENC in this document) which provides fully accelerated hardware-based video encoding and is independent of graphics/CUDA cores. With end-to-end encoding offloaded to NVENC, the graphics/CUDA cores and the CPU cores are free for other operations. For example, in a game recording scenario, offloading the encoding to NVENC makes the graphics engine fully available for game rendering. In the video transcoding use-case, video encoding/decoding can happen on NVENC/NVDEC in parallel with other video post-/pre-processing on CUDA cores.
The hardware capabilities available in NVENC are exposed through APIs referred to as NVENCODE APIs in the document. This document provides information about the capabilities of the hardware encoder and features exposed through NVENCODE APIs.
Introduction
NVENC Capabilities
NVENC can perform end-to-end encoding for H.264, HEVC 8-bit and HEVC 10-bit. This includes motion estimation and mode decision, motion compensation and residual coding, and entropy coding. It can also be used to generate motion vectors between two frames, which are useful for applications such as depth estimation, frame interpolation or encoding using other codecs not supported by NVENC. These operations are hardware accelerated by a dedicated block on GPU silicon die. NVENCODE APIs provide the necessary knobs to utilize the hardware encoding capabilities.
Table 1 summarizes the capabilities of the NVENC hardware exposed through NVENCODE APIs and Table 2 lists the features exposed in Video Codec SDK 11.1.
| Feature | Description | Kepler GPUs | 1st Gen Maxwell GPUs | 2nd Gen Maxwell GPUs | Pascal GPUs | Volta and TU117 GPUs | Ampere and Turing GPUs (except TU117) |
|---|---|---|---|---|---|---|---|
| H.264 baseline, main and high profiles | Capability to encode YUV 4:2:0 sequence and generate a H.264-bit stream. | Y | Y | Y | Y | Y | Y |
| H.264 4:4:4 encoding (only CAVLC) | Capability to encode YUV 4:4:4 sequence and generate a H.264-bit stream. | N | Y | Y | Y | Y | Y |
| H.264 lossless encoding | Lossless encoding. | N | Y | Y | Y | Y | Y |
| H.264 motion estimation (ME) only mode | Capability to provide macro-block level motion vectors and intra/inter modes. | N | Y | Y | Y | Y | Y |
| H.264 field encoding | Capability to encode field content. | Y | Y | Y | Y | Y | N |
| H.264/HEVC weighted prediction | Support for weighted prediction. | N | N | N | Y | Y | Y |
| Encoding support for H.264 ARGB content | Capability to encode RGB input. | Y | Y | Y | Y | Y | Y |
| Multiple reference frames for H.264 | Capability to use different reference frames | N | N | N | N | N | Y |
| HEVC main profile | Capability to encode YUV 4:2:0 sequence and generate a HEVC bit stream. | N | N | Y | Y | Y | Y |
| HEVC lossless encoding | Lossless encoding. | N | N | N | Y | Y | Y |
| HEVC main10 profile | Support for encoding 10-bit content generate a HEVC bit stream. | N | N | N | Y | Y | Y |
| HEVC 4:4:4 encoding | Capability to encode YUV 4:4:4 sequence and generate a HEVC bit stream. | N | N | N | Y | Y | Y |
| HEVC motion estimation (ME) only mode | Capability to provide CTB level motion vectors and intra/inter modes. | N | N | N | Y | Y | Y |
| HEVC 8K encoding | Support for encoding 8192 × 8192 Content. | N | N | N | Y* | Y | Y |
| HEVC sample adaptive offset (SAO) | Improves encoded video quality. | N | N | N | Y | Y | Y |
| HEVC B frame | Improves encoded quality | N | N | N | N | N | Y |
| Multiple reference frames for HEVC | Capability to use different reference frames | N | N | N | N | N | Y |
- Y: Supported, N: Not supported
- *Supported in select Pascal generation GPUs
| New Feature | Description |
|---|---|
| DirectX 12 support for H.264 and HEVC encode | Video Codec SDK 11.1 introduces DirectX 12 support for encode (on Windows 20H1 and later OS). This enables applications to pass DirectX 12 input and output buffers to NVENC HW encoder. |
| Chroma QP offset support for H.264 and HEVC | Video Code SDK 11.1 introduces support for specifying value of 'chroma_qp_index_offset' and 'second_chroma_qp_index_offset' in H.264 and 'pps_cb_qp_offset' and 'pps_cr_qp_offset' in HEVC. |
| Single slice in frames during intra refresh for H.264 and HEVC | Video Code SDK 11.1 introduces support for maintaining single slice in frames during intra refresh in H.264 and HEVC. |
NVENC Licensing Policy
There is no change in licensing policy in the current SDK in comparison to the previous SDK. The licensing policy is as follows:
As far as NVENC hardware encoding is concerned, NVIDIA GPUs are classified into two categories: “qualified” and “non-qualified”. On qualified GPUs, the number of concurrent encode sessions is limited by available system resources (encoder capacity, system memory, video memory etc.). On non-qualified GPUs, the number of concurrent encode sessions is limited to 3 per system. This limit of 3 concurrent sessions per system applies to the combined number of encoding sessions executed on all non-qualified cards present in the system.
For a complete list of qualified and non-qualified GPUs, refer to https://developer.nvidia.com/nvidia-video-codec-sdk..
For example, on a system with one Quadro RTX4000 card (which is a qualified GPU) and three GeForce cards (which are non-qualified GPUs), the application can run N simultaneous encode sessions on Quadro RTX4000 card (where N is defined by the encoder/memory/hardware limitations) and 3 sessions on all the GeForce cards combined. Thus, the limit on the number of simultaneous encode sessions for such a system is N + 3.
NVENC Performance
With every generation of NVIDIA GPUs (Maxwell 1st/2nd gen, Pascal, Volta, Turing and Ampere), NVENC performance has increased steadily. Table 3 provides indicative1 NVENC performance on Maxwell, Pascal, Turing and Ampere GPUs for different presets and rate control modes (these two factors play a major role in determining the performance and quality). Note that performance numbers in Table 3 are measured on GeForce hardware with assumptions listed under the table. The performance varies across GPU classes (e.g. Quadro, Tesla), and scales (almost) linearly with the clock speeds for each hardware.
While first-generation Maxwell GPUs had one NVENC engine per chip, certain variants of the second-generation Maxwell, Pascal and Volta GPUs have two/three NVENC engines per chip. This increases the aggregate encoder performance of the GPU. NVIDIA driver takes care of load balancing among multiple NVENC engines on the chip, so that applications don’t require any special code to take advantage of multiple encoders and automatically benefit from higher encoder capacity on higher-end GPU hardware. The encode performance listed in Table 3 is given per NVENC engine. Thus, if the GPU has 2 NVENCs (e.g. GP104, GM204), multiply the corresponding number in Table 3 by the number of NVENCs per chip to get aggregate maximum performance (applicable only when running multiple simultaneous encode sessions). Note that performance with single encoding session cannot exceed performance per NVENC, regardless of the number of NVENCs present on the GPU.
NVENC hardware natively supports multiple hardware encoding contexts with negligible context-switching penalty. As a result, subject to the hardware performance limit and available memory, an application can encode multiple videos simultaneously. NVENCODE API exposes several presets, rate control modes and other parameters for programming the hardware. A combination of these parameters enables video encoding at varying quality and performance levels. In general, one can trade performance for quality and vice versa.
| Preset | RC Mode | Tuning Info | H.264 | HEVC | ||||
|---|---|---|---|---|---|---|---|---|
| Maxwell (M2000) | Pascal (P2000) | Turing (RTX8000) | Maxwell (M2000) | Pascal (P2000) | Turing (RTX8000) | |||
| P1 | CBR | LL | 472 | 676 | 766 | 275 | 532 | 849 |
| VBR | HQ | 479 | 694 | 749 | 239 | 499 | 837 | |
| P3 | CBR | LL | 454 | 658 | 550 | 228 | 436 | 421 |
| VBR | HQ | 292 | 393 | 546 | 226 | 435 | 504 | |
| P5 | CBR | LL | 262 | 361 | 219 | 205 | 364 | 277 |
| VBR | HQ | 216 | 323 | 216 | 204 | 363 | 304 | |
| P7 | CBR | LL | 219 | 319 | 194 | 189 | 338 | 277 |
| VBR | HQ | 160 | 243 | 180 | 151 | 260 | 154 | |
- Resolution/Input Format/Bit depth: 1920 × 1080/YUV 4:2:0/8-bit
- All the measurement is done on the highest video clocks as reported by nvidia-smi (i.e. 1129 MHz, 1683 MHz, 1755 MHz for M2000, P2000 and RTX8000 respectively). The performance should scale according to the video clocks as reported by nvidia-smi for other GPUs of every individual family. Information on nvidia-smi can be found at https://developer.nvidia.com/nvidia-system-management-interface.
- The encoding performance on Ampere GPUs scales up with the performance numbers on Turing GPUs in proportion to the highest video clocks as reported by nvidia-smi.
- The encoding performance on Volta GPUs scales up with the performance numbers on Pascal GPUs in proportion to the highest video clocks as reported by nvidia-smi.
- Software: Windows 10 20H1, Video Codec SDK 11.1, NVIDIA display driver: 471.41
- CBR: Constant bitrate rate control mode, VBR: Variable bitrate rate control mode, LL : Low latency tuning info, HQ: High quality tuning info
Programming NVENC
Video Codec SDK 11.1 is supported on R470 and above drivers on Windows and Linux. Refer to the SDK release notes for information regarding the required driver version.
Refer to the documents and the sample applications included in the SDK package for details on how to program NVENC.
FFmpeg Support
FFmpeg is the most popular multimedia transcoding tool used extensively for video and audio transcoding.
The video hardware accelerators in NVIDIA GPUs can be effectively used with FFmpeg to significantly speed up the video decoding, encoding and end-to-end transcoding at very high performance.
Note that FFmpeg is open-source project and its usage is governed by specific licenses and terms and conditions for FFmpeg.
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