TransparentComposition class

Transparent composition with silent audio.

Generating silent audio has proven to be a very difficult and buggy thing to do with FFMPEG. To do things in a way that seems to play nice with FFMPEG, this composition combines two different tools to generate silent audio.

First, one second of audio is taken from "invisible.mov", a transparent and silent video that plays for one second.

Second, an anullsrc audio stream is tacked on after the real audio sample to fill up any remaining time for this composition.

This approach came from an investigation into why noise was appearing in videos after a silent portion, when that silent portion is the very first thing to appear in a given FFMPEG stream. My theory is that FFMPEG is choosing a very low bitrate, or a weird encoding, or a bad sample size based on the fact that the first audio sample is anullsrc, and then that same decision is applied to the real video that follows, which degrades the video's audio.

Therefore, by playing 1 second (or any length) of real, silent audio, and then introducing anullsrc after that, we convince FFMPEG to use audio settings that are good enough for video. So that's the approach taken with this composition when it comes to silent audio.

This is all a theory based on debugging. I'm not sure about the root cause, but the silent audio + anullsrc seems to solve the problem.

Implemented types

• Composition

Constructors

TransparentComposition({bool hasVideo = true, bool hasAudio = true, required Duration duration})

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

build(FfmpegBuilder builder, CompositionSettings settings) → Future<FfmpegStream>

Adds this composition to the composition tree in the given builder.

override

computeIntrinsicDuration() → Future<Duration>

Computes the natural, or intrinsic, duration of this composition.

override

computeIntrinsicSize() → Future<VideoSize>

Computes the natural, or intrinsic, size of this composition.

override

createDiagnosticsNode() → DiagnosticsNode

override

hasAudio() → Future<bool>

Whether this composition includes any audio streams.

override

hasVideo() → Future<bool>

Whether this composition includes any video frames.

override

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited