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Overview

Ant Media Server provides real-time adaptive bitrate (ABR) transcoding, allowing you to deliver streams at multiple quality levels. This ensures viewers get the best possible experience based on their network conditions and device capabilities. The transcoding engine is powered by FFmpeg and can encode streams in real-time with GPU acceleration support.

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How It Works

When transcoding is enabled, Ant Media Server:
  1. Receives the source stream (typically at the highest quality)
  2. Encodes multiple renditions at different resolutions and bitrates
  3. Packages all renditions into HLS/DASH playlists
  4. Allows players to switch between qualities based on network conditions
Transcoding workflow

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Encoder Settings

Transcoding profiles are defined using the EncoderSettings class: 
public class EncoderSettings {
    private int height;              // Resolution height in pixels
    private int videoBitrate;        // Video bitrate in kbps
    private int audioBitrate;        // Audio bitrate in kbps
    private boolean forceEncode;     // Force encoding even if source is lower quality
    
    public EncoderSettings(int height, int videoBitrate, 
                          int audioBitrate, boolean forceEncode) {
        this.height = height;
        this.videoBitrate = videoBitrate;
        this.audioBitrate = audioBitrate;
        this.forceEncode = forceEncode;
    }
}

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Parameters Explained

ParameterDescriptionExample
heightTarget resolution height (width calculated automatically)360, 480, 720, 1080
videoBitrateTarget video bitrate in kbps500, 1000, 2500
audioBitrateTarget audio bitrate in kbps64, 128
forceEncodeEncode even if source resolution is lowertrue, false
forceEncode=false prevents upscaling. If the source is 720p and you request 1080p with forceEncode=false, that rendition will be skipped.

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Configuration

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Via Web Panel

Navigate to Settings → Advanced Settings and configure:
  1. Enable Adaptive Bitrate Streaming
  2. Add encoder settings as JSON array:
[
  {"height": 360, "videoBitrate": 600, "audioBitrate": 64, "forceEncode": false},
  {"height": 480, "videoBitrate": 1000, "audioBitrate": 96, "forceEncode": false},
  {"height": 720, "videoBitrate": 2000, "audioBitrate": 128, "forceEncode": false},
  {"height": 1080, "videoBitrate": 4000, "audioBitrate": 128, "forceEncode": false}
]

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Via REST API

Update application settings: 
curl -X PUT "http://localhost:5080/LiveApp/rest/v2/applications/settings/LiveApp" \
  -H "Content-Type: application/json" \
  -d '{
    "adaptiveResolutionList": [
      {"height": 360, "videoBitrate": 600, "audioBitrate": 64},
      {"height": 720, "videoBitrate": 2000, "audioBitrate": 128}
    ]
  }'

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Per-Stream Configuration

You can also set encoding profiles for individual streams: 
curl -X POST "http://localhost:5080/LiveApp/rest/v2/broadcasts/create" \
  -H "Content-Type: application/json" \
  -d '{
    "streamId": "stream123",
    "name": "My Stream",
    "encoderSettingsList": [
      {"height": 360, "videoBitrate": 600, "audioBitrate": 64},
      {"height": 720, "videoBitrate": 2000, "audioBitrate": 128}
    ]
  }'

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Adaptive Stream Structure

When transcoding is active, the MuxAdaptor creates multiple output streams: 
public class MuxAdaptor {
    // Original source stream
    private String streamId;  // e.g., "stream123"
    
    // Adaptive renditions
    List<EncoderSettings> adaptiveResolutionList;
    
    // Generated stream IDs:
    // stream123        - source quality
    // stream123_240p   - 240p rendition  
    // stream123_360p   - 360p rendition
    // stream123_480p   - 480p rendition
    // stream123_720p   - 720p rendition
    // stream123_adaptive - master playlist (HLS/DASH)
}

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Output Files

For a stream with ID stream123, transcoding produces: 
streams/
├── stream123.m3u8              # Source quality playlist
├── stream123_240p.m3u8          # 240p playlist
├── stream123_360p.m3u8          # 360p playlist  
├── stream123_720p.m3u8          # 720p playlist
└── stream123_adaptive.m3u8      # Master playlist (ABR)
Always use the _adaptive.m3u8 playlist in your player for automatic quality switching.

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GPU Acceleration

Ant Media Server supports hardware-accelerated encoding:

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NVIDIA GPU (NVENC)

Enable in application settings: 
{
  "encoderSettings": "h264_nvenc",
  "h264Enabled": true
}

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Intel Quick Sync (QSV)

{
  "encoderSettings": "h264_qsv"
}

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Performance Comparison

Encoder1080p StreamCPU UsageLatency
Software (x264)4 renditions~80%Less than 3s
NVIDIA NVENC4 renditions~20%Less than 2s
Intel QSV4 renditions~25%Less than 2s
GPU encoding trades some quality for performance. For best quality, use software encoding with optimized presets.

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Transcoding Modes

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Real-time Transcoding

Default mode - streams are transcoded as they arrive: 
// Configured in AppSettings
private boolean hlsMuxingEnabled = true;
private boolean dashMuxingEnabled = false;
private List<EncoderSettings> adaptiveResolutionList;

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VOD Transcoding

Recorded files can be transcoded after the stream ends: 
curl -X POST "http://localhost:5080/LiveApp/rest/v2/vods/{vodId}/transcode" \
  -H "Content-Type: application/json" \
  -d '{
    "resolutions": [360, 480, 720]
  }'

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Quality Ladder Recommendations

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Standard Ladder (Mobile + Desktop)

[
  {"height": 240, "videoBitrate": 400, "audioBitrate": 64, "forceEncode": false},
  {"height": 360, "videoBitrate": 800, "audioBitrate": 96, "forceEncode": false},
  {"height": 480, "videoBitrate": 1400, "audioBitrate": 128, "forceEncode": false},
  {"height": 720, "videoBitrate": 2800, "audioBitrate": 128, "forceEncode": false},
  {"height": 1080, "videoBitrate": 5000, "audioBitrate": 192, "forceEncode": false}
]

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Mobile-Only Ladder

[
  {"height": 240, "videoBitrate": 400, "audioBitrate": 64},
  {"height": 360, "videoBitrate": 800, "audioBitrate": 96},
  {"height": 480, "videoBitrate": 1200, "audioBitrate": 128}
]

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4K Streaming Ladder

[
  {"height": 480, "videoBitrate": 1400, "audioBitrate": 128},
  {"height": 720, "videoBitrate": 2800, "audioBitrate": 128},
  {"height": 1080, "videoBitrate": 5000, "audioBitrate": 192},
  {"height": 1440, "videoBitrate": 9000, "audioBitrate": 192},
  {"height": 2160, "videoBitrate": 16000, "audioBitrate": 256}
]

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Monitoring Transcoding

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Check Stream Resolutions

curl "http://localhost:5080/LiveApp/rest/v2/broadcasts/{streamId}"
Response includes active renditions: 
{
  "streamId": "stream123",
  "subTrackStreamIds": [
    "stream123_240p",
    "stream123_360p",
    "stream123_720p"
  ]
}

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Server Resources

Monitor CPU/GPU usage: 
curl "http://localhost:5080/LiveApp/rest/v2/system-resources"

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Troubleshooting

Check:
  • Encoder settings are properly configured
  • Source stream resolution is higher than target
  • forceEncode is set correctly
  • FFmpeg is properly installed
Solution: Enable DEBUG logging for io.antmedia.muxer.MuxAdaptor
Causes:
  • Too many renditions configured
  • Software encoding without GPU
  • Source resolution too high
Solutions:
  • Reduce number of renditions
  • Enable GPU acceleration (NVENC/QSV)
  • Use faster encoding presets
Issue: Player doesn’t switch between qualitiesCauses:
  • Using wrong playlist (not _adaptive.m3u8)
  • Player doesn’t support ABR
  • Network conditions stable
Solution: Ensure you’re using the master playlist and a modern player (HLS.js, Video.js, etc.)

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Best Practices

Start Conservative

Begin with 2-3 renditions and add more based on viewer analytics and server capacity.

Match Your Audience

Configure renditions based on your viewers’ devices and network conditions.

Use GPU Encoding

Enable hardware acceleration for high-volume streams to reduce CPU load.

Test Quality Ladder

Validate visual quality at each bitrate using actual devices and network conditions.

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