Custom arguments¶

Every FFmpeg adapter and every standalone encoder exposes a Custom arguments field at the bottom of its Options tab, for the flags the curated options do not cover.

The field is parsed into an argument list and never run through a shell. Shell metacharacters are not interpreted, so quoting behaves like a command line, not like bash.

Write one argument group per line:

-cutoff 18000
pre: -analyzeduration 200M
var gain = 3
-af {filters},volume={gain}dB

Slots: where a line lands¶

An unprefixed line is applied after the managed codec settings, which is where custom arguments have always gone. Prefix a line to put it somewhere else.

Prefix	Where it lands	Available on
(none) or `out:`	After the managed codec settings	Every adapter
`pre:`	Before `-i`, for `-hwaccel`, `-analyzeduration`, `-guess_layout_max`	Every adapter
`decode:`	The FFmpeg decode stage's output side	opusenc, qaac, fdkaac

decode: exists because the standalone encoders run a two-stage pipeline - FFmpeg decodes the source to PCM and pipes it to the encoder. Without it, the hand-off between the two would be unreachable. decode: -c:a pcm_f32le changes the PCM format the encoder receives; an unprefixed line still goes to the encoder itself.

Placeholders¶

{name} expands to a value the application is already managing.

Every option on the encoder is a placeholder under its own name, so {bitrate_kbps} is whatever the Bitrate control currently reads.
{filters} is the managed filter chain - the gain, tempo and delay filters combined.
{sample_rate}, {channel_layout}, {codec} and {stream} cover the General tab.

The input and output paths are deliberately not placeholders. The queue writes to a temporary file and renames it into place when the encode succeeds, and reaching that path would break the guarantee that a failed encode never leaves a half-written file behind.

Write {{ for a literal brace.

Extending the filter chain instead of replacing it¶

This is the one to know. -af is a single FFmpeg option, so a bare -af of your own replaces the managed chain and your gain, tempo and delay silently stop being applied.

-af {filters},highpass=f=20      ← extends: gain, tempo and delay are kept
-af highpass=f=20                ← replaces: they are lost

Both are allowed - the second is occasionally what you want - but the command preview says which one you got, and warns loudly about the second.

If there is no managed chain, {filters} expands to nothing and the stray comma is cleaned up, so the first line above stays valid on a file with no gain, tempo or delay set.

Variables¶

A var name = value line declares a variable that the rest of the field can use. The declaration lives in the same field as the use, so a preset can never carry one without the other.

var cutoff = 18000
-cutoff {cutoff}

A variable that is defined but empty drops the whole argument group that uses it:

var cutoff =
-cutoff {cutoff} -aac_coder fast

emits -aac_coder fast and nothing else - not a malformed -cutoff "". That makes a flag easy to switch off by blanking one line rather than deleting and retyping it.

A placeholder that is never defined is an error, not a silent omission. A typo would otherwise quietly change your command.

Overriding a managed setting¶

A custom flag that collides with one the application manages replaces it, rather than being appended alongside it. Setting -b:a 256k gives you exactly one -b:a in the command, and the preview reports what it displaced:

⚠ -b:a 256k overrides Bitrate (192k)

Alternative spellings count as the same flag: -filter:a collides with the managed -af, and -acodec with -c:a. Emitting both spellings would make FFmpeg fail outright.

Repeated flags of your own are all kept - two -metadata lines stay two -metadata arguments - because only managed arguments are ever displaced.

What cannot be set¶

A few arguments are refused with an explanation, because the application's guarantees depend on them:

Refused	Why
`-i`, `-map`, `-map_chapters`	The input and stream selection come from the input list and the General tab
`-progress`, `-nostats`, `pipe:N`	Progress reporting and the pipeline between stages are parsed by the application
`-f`, `-o`, a bare `-` in an output slot	The container and output path are managed so a finished encode can be published atomically
A line that does not start with a flag	FFmpeg would read a bare value as an extra output file and write something you did not ask for

-f is allowed in the pre: slot, where it forces the input demuxer rather than the output muxer.

Mistakes are reported when you type them, in the command preview, and again when the job is queued - never at encode time only.

DeeZy is different¶

The DeeZy adapters keep a much narrower field: Advanced downmix metadata, restricted to Lt/Rt and Lo/Ro level flags. Slots, placeholders and variables do not apply there. These drive licensed Dolby encodes through the Dolby Encoding Engine, where a stray argument produces an expensive, subtly wrong result rather than an obvious failure.

Presets¶

The field is saved in presets along with everything else, variables included.