Stuttering audio in MediaConvert output when transcoding PCM to AAC

Question

Hi,

I’m seeing stuttering audio in the output when transcoding a file with PCM audio to AAC using AWS MediaConvert.

During the job, MediaConvert reports the following warning:

```
MediaConvert added at least 100 milliseconds of audio silence to keep audio and video in sync
```

The job completes successfully, but the resulting output video has noticeable audio stuttering. I haven’t been able to find a reliable workaround so far.

**MediaConvert Job ID**: 1769175980184-55oivp

**Settings for MediaConvert output**

` {
  "Queue": "arn:aws:mediaconvert:us-east-1:611176567156:queues/Default",
  "UserMetadata": {},
  "Role": "arn:aws:iam::611176567156:role/service-role/MediaConvert_Default_Role",
  "Settings": {
    "TimecodeConfig": {
      "Source": "EMBEDDED"
    },
    "OutputGroups": [
      {
        "CustomName": "Test",
        "Name": "File Group",
        "Outputs": [
          {
            "ContainerSettings": {
              "Container": "MP4",
              "Mp4Settings": {}
            },
            "VideoDescription": {
              "CodecSettings": {
                "Codec": "H_264",
                "H264Settings": {
                  "MaxBitrate": 8000000,
                  "RateControlMode": "QVBR",
                  "SceneChangeDetect": "TRANSITION_DETECTION"
                }
              }
            },
            "AudioDescriptions": [
              {
                "CodecSettings": {
                  "Codec": "AAC",
                  "AacSettings": {
                    "Bitrate": 96000,
                    "CodingMode": "CODING_MODE_2_0",
                    "SampleRate": 48000
                  }
                }
              }
            ]
          }
        ],
        "OutputGroupSettings": {
          "Type": "FILE_GROUP_SETTINGS",
          "FileGroupSettings": {
            "Destination": "/",
            "DestinationSettings": {
              "S3Settings": {
                "StorageClass": "STANDARD"
              }
            }
          }
        }
      }
    ],
    "FollowSource": 1,
    "Inputs": [
      {
        "AudioSelectors": {
          "Audio Selector 1": {
            "DefaultSelection": "DEFAULT"
          }
        },
        "VideoSelector": {},
        "TimecodeSource": "ZEROBASED",
        "FileInput": ""
      }
    ]
  },
  "BillingTagsSource": "JOB",
  "AccelerationSettings": {
    "Mode": "PREFERRED"
  },
  "StatusUpdateInterval": "SECONDS_60",
  "Priority": 0
}
`

re:Post Agent · Answer

The stuttering audio issue you're experiencing is likely related to audio-video synchronization problems that MediaConvert is trying to correct. The warning message "MediaConvert added at least 100 milliseconds of audio silence to keep audio and video in sync" indicates that the service is detecting timing discrepancies between your audio and video tracks.

This is a known behavior when MediaConvert encounters misalignment between audio and video tracks in the input file. To maintain proper synchronization, MediaConvert adds silence to the audio track, which can sometimes result in the stuttering effect you're observing.

There are a few potential solutions you could try:

1. Adjust the audioDuration setting: In your MP4 output container settings, you can specify the audioDuration parameter. By default, it uses "Default codec duration," but you could try setting it to "Match video duration." This setting is specifically designed for workflows that are sensitive to small duration differences between video and audio.

2. Check your timecode configuration: There appears to be a discrepancy in your job settings. Your TimecodeConfig source is set to "EMBEDDED" but your input TimecodeSource is set to "ZEROBASED." This inconsistency might be contributing to the sync issues. Try making these settings consistent.

3. Examine your input file: The warning suggests there might be issues with the input file's audio and video track alignment. You might want to analyze the source file to see if there are inherent timing problems that MediaConvert is trying to correct.

If these solutions don't resolve the issue, you may need to preprocess your input file to ensure better audio-video alignment before submitting it to MediaConvert.  
**Sources**  
[Warning codes - MediaConvert](https://docs.aws.amazon.com/mediaconvert/latest/ug/warning_codes.html)  
[Presets name - AWS Elemental MediaConvert API Reference](https://docs.aws.amazon.com/mediaconvert/latest/apireference/presets-name.html)  
[Setting up timecodes - MediaConvert](https://docs.aws.amazon.com/mediaconvert/latest/ug/setting-up-timecode.html)  
[Sample Job Settings Specifications in JSON - AWS Elemental MediaConvert API Reference](https://docs.aws.amazon.com/mediaconvert/latest/apireference/sample-json.html)

Stuttering audio in MediaConvert output when transcoding PCM to AAC

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