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Module 7.6 – MP4 Export

  • Updated

Topics covered in this article: 

  • The MP4 export function 
  • Custom video in an MP4 export 
  • Exporting an MP4 file 

 

Introduction 

The Dolby Atmos Renderer allows the user to export an MP4 file.  

The primary use case for the MP4 export is QC of the encoded Dolby Atmos mix on consumer playback equipment, e.g., audio/video receiver (AVR) or Soundbar.  

A few examples of how this can be done include: 

  • Transferring the MP4 file to a USB flash drive and playing back via a Blu-ray player with the audio set to bitstream passthrough.
  • Playback via the Safari browser airplay’ed to an AppleTV4k.
  • Playback in the Dolby Reference Player application. 

The MP4 can also be used as the master for packaging streaming media. 

MP4 files are exported from an open master file (48kHz only). 

The exported MP4 files contain an audio track and a few options for a video track: 

  • The audio track is encoded from the open Master File. Use the encoding mode applicable for the content. 
    • The Music encoding mode encodes a DD+JOC file at a bit rate of 768kbps using the Music Light Dynamic Range Control profile. 
    • The Film encoding mode encodes a DD+JOC file at a user selectable bit rate of 448kbps or 768kbps using the Film Light Dynamic Range Control profile. 
  • The video track in the MP4 file can be: 
    • Black video at 720p resolution and 24fps encoded with the h264 video codec. The frame rate is independent of the frame rate of the open Master file. This option is required for most consumer devices (which require a video track for playback). 
    • No video, for use where an audio-only MP4 file is required 
    • Custom video  

 

Custom Video in MP4 Exports 

Multiplexing custom video into the MP4 was introduced with the Renderer v3.7 and provides a way to QC an MP4 with video and Dolby Atmos audio. 

Note that while the audio export in/out points can be set manually to trim any pre and/or post roll, there is no such control for custom video. To ensure playback is in sync, the start point of the video must match the In point of the Atmos Master or manually set in point.  

If additional silence is required for the Atmos Master this can be added using the Dolby Atmos Conversion Tool. 

Custom video requirements: 

  • The video container/file format supported is .mp4 or elementary video .h264 
  • The only video codec supported is h264 
  • The video frame rate must match the frame rate of the open Master file 

Any audio in the MP4 will be discarded. If the custom video does not match the duration of the open Atmos Master, the duration of the resulting MP4 will conform to the longer duration of either the Atmos Master or the custom video file.         

Dialog/notification boxes will appear if the custom video file cannot be used, if the frame rate does not match, or if the video file does not match the duration of the selected audio export.

Exporting an MP4 File 

To export an MP4 file: 

  • Load a master file (48kHz only).
  • From the menu bar, navigate to File>Export MP4 or type Command+Shift+M (Mac) or Ctrl+Shift+M (Windows). 

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  • Choose an output directory. 
  • Enter a file name. 
  • In the Export settings: 
    • From the Encoding Mode section 
      • Select which Dynamic Range Control profile to use based on the type of content. 
      • If using Film mode, choose between a bit rate of 448kbps or 768kbps (default). 
    • From the Export In/Out 
      • Set to Entire master or Set Manually and enter In Out points 
  • In the Video Section 
    • Select the video option to be used for the export 
    • If using Custom video, browse to the location of the video file to be used
  • Click Export 

 

 

Navigation 

Next:  Module 8.1 - Module Objectives  

Previous:  Module 7.5 – Exporting and Importing Input/Binaural/Re-Render Configuration Files