# ismlmux

This element merges streams (audio and video) into ISML (.isml) files.

The following background intends to explain why various similar muxers are present in this plugin.

The QuickTime file format specification served as basis for the MP4 file format specification (mp4mux), and as such the QuickTime file structure is nearly identical to the so-called ISO Base Media file format defined in ISO 14496-12 (except for some media specific parts).

In turn, the latter ISO Base Media format was further specialized as a Motion JPEG-2000 file format in ISO 15444-3 (mj2mux) and in various 3GPP(2) specs (3gppmux). The fragmented file features defined (only) in ISO Base Media are used by ISMV files making up (a.o.) Smooth Streaming (ismlmux).

A few properties (#GstBaseQTMux:movie-timescale, trak-timescale) allow adjusting some technical parameters, which might be useful in (rare) cases to resolve compatibility issues in some situations.

Some other properties influence the result more fundamentally. A typical mov/mp4 file's metadata (aka moov) is located at the end of the file, somewhat contrary to this usually being called "the header". However, a faststart file will (with some effort) arrange this to be located near start of the file, which then allows it e.g. to be played while downloading. Alternatively, rather than having one chunk of metadata at start (or end), there can be some metadata at start and most of the other data can be spread out into fragments of fragment-duration. If such fragmented layout is intended for streaming purposes, then streamable allows foregoing to add index metadata (at the end of file).

For AV1 muxing, see the “AV1 compatibility note” section under qtmux.

## Example pipelines

     gst-launch-1.0 videotestsrc num-buffers=50 ! queue ! x264enc ! ismlmux fragment-duration=10 ! filesink location=video.isml

Records a video stream captured from a v4l2 device, encodes it into H.264 and muxes it into an isml file.

Documentation last reviewed on 2011-04-21

## Hierarchy

    GObject
        ╰──GInitiallyUnowned
            ╰──GstObject
                ╰──GstElement
                    ╰──GstAggregator
                        ╰──GstBaseQTMux
                            ╰──ismlmux

## Implemented interfaces

    GstTagSetter
    GstTagXmpWriter
    GstPreset

## Factory details

Authors: – Thiago Sousa Santos

Classification: – `Codec/Muxer`

Rank – primary

Plugin – isomp4

Package – GStreamer Good Plug-ins

## Pad Templates

### `audio_%u`

    audio/mpeg:
        mpegversion: 1
              layer: 3
           channels: [ 1, 2 ]
               rate: [ 1, 2147483647 ]
    audio/mpeg:
        mpegversion: 4
      stream-format: raw
           channels: [ 1, 8 ]
               rate: [ 1, 2147483647 ]

Presence – request

Direction – sink

Object type – GstQTMuxPad

### `src`

    video/quicktime:
            variant: iso-fragmented

Presence – always

Direction – src

Object type – GstAggregatorPad

### `video_%u`

    video/mpeg:
        mpegversion: 4
       systemstream: false
              width: [ 16, 2147483647 ]
             height: [ 16, 2147483647 ]
    video/x-divx:
        divxversion: 5
              width: [ 16, 2147483647 ]
             height: [ 16, 2147483647 ]
    video/x-h264:
      stream-format: { (string)avc, (string)avc3 }
          alignment: au
              width: [ 16, 2147483647 ]
             height: [ 16, 2147483647 ]

Presence – request

Direction – sink

Object type – GstQTMuxPad

## Properties

### streamable

    “streamable” gboolean

If set to true, the output should be as if it is to be streamed and hence no indexes written or duration written.

Flags : Read / Write / Construct

Default value : true

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