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

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Encoder Settings Object

Each encoder profile consists of four main parameters:
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height
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.
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videoBitrate
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
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audioBitrate
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
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forceEncode
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.

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Configuration Methods

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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
  }
]

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Via Web Panel

Encoder settings can be configured through the Ant Media Server web panel:
  1. Navigate to your application settings
  2. Go to the Adaptive Bitrate section
  3. Add or modify encoder profiles
  4. Save changes

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Video Encoder Configuration

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Encoder Selection

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encoderName
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
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encoderSelectionPreference
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

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Encoder Parameters

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encoderParameters
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"
  }
}

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Thread Configuration

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encoderThreadCount
int
default:"0"
Number of threads for encoding. 0 means auto-detect.
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encoderThreadType
int
default:"0"
Thread type for encoding:
  • 0 - Auto
  • 1 - Frame-based threading
  • 2 - Slice-based threading

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Codec Support

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H.264

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h264Enabled
boolean
default:"true"
Enable/disable H.264 encoding.

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H.265 (HEVC)

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h265Enabled
boolean
default:"false"
Enable/disable H.265/HEVC encoding.

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VP8

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vp8Enabled
boolean
default:"false"
Enable/disable VP8 encoding.
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vp8EncoderThreadCount
int
default:"1"
Number of threads for VP8 encoder.

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Audio Configuration

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AAC Encoding

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aacEncodingEnabled
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.
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audioBitrateSFU
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.

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GOP and Quality Settings

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gopSize
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.
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forceAspectRatioInTranscoding
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

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Hardware Acceleration

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

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Common Encoder Profiles

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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}
]

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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}
]

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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}
]

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Conference/Webinar (Speaker + Attendees)

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

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SFU Mode vs Transcoding

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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

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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

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Best Practices

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

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