Configure DASH Segment Duration and Manifest Name in FFmpeg

This article provides a quick guide on how to customize the segment duration and manifest file name when packaging video content using the FFmpeg MPEG-DASH muxer. By configuring these settings, you can optimize streaming latency, compatibility, and file organization for your media delivery pipeline.

To configure DASH output in FFmpeg, you must use the DASH muxer by specifying -f dash. Controlling the segment duration and manifest name involves utilizing specific muxer private options.

Setting the Segment Duration

To define the length of each media segment, use the -seg_duration option. This option accepts a value in seconds (which can be a decimal).

For example, to set a segment duration of 4 seconds, add the following to your command:

-seg_duration 4

By default, FFmpeg will attempt to cut segments at the nearest keyframe (I-frame) close to this duration. To ensure precise segment lengths, you should force keyframe intervals (GOP size) in your video encoder settings to align with your target segment duration. For example, if your video is 30 frames per second (fps) and you want 4-second segments, set the GOP size to 120 using -g 120 -keyint_min 120 -sc_threshold 0.

Setting the Manifest Name

The name of the main DASH manifest file (the .mpd file) is determined by the output file path specified at the very end of your FFmpeg command.

For example, to name your manifest live_stream.mpd, specify it as the output target:

live_stream.mpd

Customizing Segment File Names

In addition to the manifest name, you can customize how the individual initialization and media segment files are named using the -init_seg_name and -media_seg_name options:

• -init_seg_name: Sets the template for the initialization segments (default is init-stream$RepresentationID$.m4s).
• -media_seg_name: Sets the template for the media segments (default is chunk-stream$RepresentationID$-$Number%05d$.m4s).

Complete Command Example

Below is a complete FFmpeg command that transcodes an input video, sets the segment duration to 6 seconds, names the manifest custom_manifest.mpd, and customizes the segment file names:

ffmpeg -i input.mp4 \
  -c:v libx264 -g 180 -keyint_min 180 -sc_threshold 0 \
  -c:a aac \
  -f dash \
  -seg_duration 6 \
  -init_seg_name 'init_$RepresentationID$.m4s' \
  -media_seg_name 'chunk_$RepresentationID$_$Number$.m4s' \
  custom_manifest.mpd

In this command: * -g 180 forces a keyframe every 180 frames (which equals 6 seconds of video at 30 fps), aligning perfectly with the segment duration. * -f dash selects the DASH muxer. * -seg_duration 6 instructs FFmpeg to split the streams into 6-second chunks. * custom_manifest.mpd is the output parameter that defines the name of the generated manifest.