Encoder Settings

Encoder settings define the video and audio quality profiles used for adaptive bitrate (ABR) streaming and transcoding in Ant Media Server.

Encoder Settings Object

Each encoder profile consists of four main parameters:

int

required

Video resolution height in pixels (e.g., 480, 720, 1080).The width is automatically calculated to maintain the aspect ratio of the source stream.

int

required

Video bitrate in bits per second (bps).Examples:

240p: 200,000 - 400,000 bps
360p: 300,000 - 600,000 bps
480p: 500,000 - 1,000,000 bps
720p: 1,500,000 - 3,000,000 bps
1080p: 3,000,000 - 6,000,000 bps

int

required

Audio bitrate in bits per second (bps).Typical values:

64,000 bps (64 kbps) - Low quality
96,000 bps (96 kbps) - Standard quality
128,000 bps (128 kbps) - Good quality
192,000 bps (192 kbps) - High quality

boolean

default:"true"

Enable/disable stream resolution check.If enabled, Ant Media Server will ignore adaptive resolutions higher than the incoming stream.Example: If incoming stream is 480p and you request 720p encoding with forceEncode: true, the 720p profile will be ignored.

Configuration Methods

Via encoderSettingsString

The encoderSettingsString parameter accepts a JSON array of encoder profiles:

[
  {
    "height": 720,
    "videoBitrate": 2000000,
    "audioBitrate": 128000,
    "forceEncode": true
  },
  {
    "height": 480,
    "videoBitrate": 1000000,
    "audioBitrate": 96000,
    "forceEncode": true
  },
  {
    "height": 360,
    "videoBitrate": 600000,
    "audioBitrate": 64000,
    "forceEncode": true
  }
]

Via Web Panel

Encoder settings can be configured through the Ant Media Server web panel:

Navigate to your application settings
Go to the Adaptive Bitrate section
Add or modify encoder profiles
Save changes

Video Encoder Configuration

Encoder Selection

string

default:""

Specific encoder to use for transcoding.Options:

"h264_nvenc" - NVIDIA GPU encoder (requires NVIDIA GPU)
"openh264" - OpenH264 software encoder
"libx264" - x264 software encoder
Empty string - Auto-select based on available hardware

string

default:"gpu_and_cpu"

Encoder selection strategy:

"gpu_and_cpu" - Try GPU first, fallback to CPU if GPU unavailable
"only_gpu" - Only use GPU encoder, fail if unavailable

Encoder Parameters

object

default:"{}"

Encoder-specific parameters in JSON format. Keys should match official FFmpeg encoder names.Example:

{
  "libopenh264": {
    "profile": "main"
  },
  "vpx": {
    "deadline": "realtime"
  },
  "h264_nvenc": {
    "preset": "ll"
  }
}

Thread Configuration

int

default:"0"

Number of threads for encoding. 0 means auto-detect.

int

default:"0"

Thread type for encoding:

0 - Auto
1 - Frame-based threading
2 - Slice-based threading

Codec Support

H.264

boolean

default:"true"

Enable/disable H.264 encoding.

H.265 (HEVC)

boolean

default:"false"

Enable/disable H.265/HEVC encoding.

VP8

boolean

default:"false"

Enable/disable VP8 encoding.

int

default:"1"

Number of threads for VP8 encoder.

Audio Configuration

AAC Encoding

boolean

default:"true"

Enable AAC encoding.If true, AAC encoding is active even if MP4 or HLS muxing is not enabled. Set to true if sending streams to RTMP endpoints or enabling/disabling MP4 recording on the fly.

int

default:"96000"

Audio bitrate in SFU mode for transcoding to AAC and Opus formats.After version 2.3, incoming audio is forwarded directly to viewers without transcoding when possible.

GOP and Quality Settings

int

default:"0"

Group of Pictures (GOP) size - the interval between keyframes.Important: This is NOT in seconds, but in frame count.Example: If GOP size is 50 and frame rate is 25 fps:

Keyframe interval = 50 / 25 = 2 seconds

Default value of 0 uses the incoming GOP size.

boolean

default:"false"

Force aspect ratio to match incoming stream exactly.When enabled, Ant Media Server may adjust output height to maintain perfect aspect ratio. Critical for DASH streaming with multiple bitrates.Example:

Incoming: 1280x720 (16:9)
Target: 480p
Without force: Output may be exactly 480p with slight ratio difference
With force: Output height adjusted to 853x480 for perfect 16:9

Hardware Acceleration

boolean

default:"false"

Enable GPU-based video frame scaling for adaptive bitrate.Note: Requires special build - contact Ant Media Support.

Common Encoder Profiles

Low Latency Streaming

[
  {"height": 720, "videoBitrate": 2500000, "audioBitrate": 128000, "forceEncode": true},
  {"height": 480, "videoBitrate": 1000000, "audioBitrate": 96000, "forceEncode": true},
  {"height": 360, "videoBitrate": 600000, "audioBitrate": 64000, "forceEncode": true}
]

High Quality Streaming

[
  {"height": 1080, "videoBitrate": 5000000, "audioBitrate": 192000, "forceEncode": true},
  {"height": 720, "videoBitrate": 3000000, "audioBitrate": 128000, "forceEncode": true},
  {"height": 480, "videoBitrate": 1500000, "audioBitrate": 96000, "forceEncode": true}
]

Mobile-Optimized Streaming

[
  {"height": 480, "videoBitrate": 800000, "audioBitrate": 96000, "forceEncode": true},
  {"height": 360, "videoBitrate": 500000, "audioBitrate": 64000, "forceEncode": true},
  {"height": 240, "videoBitrate": 300000, "audioBitrate": 64000, "forceEncode": true}
]

Conference/Webinar (Speaker + Attendees)

[
  {"height": 720, "videoBitrate": 1500000, "audioBitrate": 128000, "forceEncode": true},
  {"height": 360, "videoBitrate": 500000, "audioBitrate": 96000, "forceEncode": true}
]

SFU Mode vs Transcoding

SFU Mode (No Adaptive Bitrate)

If encoderSettingsString is empty or not set, Ant Media Server operates in SFU (Selective Forwarding Unit) mode:

No transcoding is performed
Original stream is forwarded directly to viewers
Lower CPU usage
Single quality available to viewers
Ideal for WebRTC-to-WebRTC streaming

Transcoding Mode (With Adaptive Bitrate)

When encoder settings are configured:

Stream is transcoded to multiple qualities
Viewers automatically receive appropriate quality based on bandwidth
Higher CPU/GPU usage
Better viewer experience across different network conditions
Required for HLS/DASH playback from WebRTC sources

Best Practices

Start with 2-3 profiles - Don’t create too many profiles initially. Monitor usage and add more if needed.
Bitrate guidelines - Use approximately 2-4 bits per pixel for good quality:
- 720p @ 30fps: 1280×720×30×3 ≈ 2,000,000 bps
Audio bitrate - 96-128 kbps is sufficient for most use cases. Use 64 kbps only for very low-bandwidth scenarios.
GOP size - Keep GOP size small (1-2 seconds) for low latency. Larger GOP reduces bandwidth but increases latency.
Hardware encoding - Use GPU encoding (h264_nvenc) when available for better performance.
Test your settings - Always test encoder settings with real streams under actual network conditions.

Get Started

Core Concepts

Deployment

Configuration

Streaming

Features

Security

Storage

SDKs

Operations