AAC is Advanced Audio Coding on its own, lossy, and the encoding that replaced MP3 nearly everywhere it mattered. OGG is an Ogg container carrying Vorbis audio, lossy, and free of the patents that hung over MP3 for twenty years. ffmpeg sits between the two, and this page says exactly what happens to an AAC file on the way to becoming an OGG one.
What runs when an AAC file becomes OGG
ffmpeg held to a single thread, on a machine we rent and watch. Your AAC file is uploaded once, ffmpeg runs once, the OGG comes back, and neither file is kept. AAC to OGG is one of the 3649 pairs that engine was probed on with a real file, which is why it has a page here and why the pairs the probe could not prove do not.
What survives from the AAC into the OGG
The running time and the channel layout. A stereo AAC comes back as a stereo OGG of the same length: this is a re-encode, not an edit, and nothing here normalises, trims or boosts the AAC.
Everything the AAC still had. ffmpeg decodes the AAC in full before it writes a single byte of OGG, so nothing is skipped on the way in, whatever was already missing.
What AAC to OGG costs you
Generation loss, and it is the whole story of this pair. AAC threw information away to be small, OGG throws more away on top of what is left, and neither pass can restore what the other removed. Converting the OGG back to AAC afterwards makes it worse a third time, not better.
Album art, where the AAC carried any. ffmpeg passes -vn on every audio target here, which counts an embedded cover as a video stream and drops it along with the film it was never part of. That is deliberate rather than careless: keeping it makes the mux fail outright on several audio containers, and hiding the choice would be lying by omission.
Any hope of OGG sounding better than the AAC. Nothing in this pass adds information, and a bitrate higher than the AAC deserved only makes a larger file of the same recording.
If a model is going to read the OGG
An OGG file is a waveform, and a language model reads text, so handing an assistant this OGG directly gets you nothing. The OGG becomes useful the moment somebody turns the sound into words, and that is a separate job with its own page here. AAC to OGG is the step before it: get the sound out of the AAC in a container the transcriber accepts, then hand the model a transcript instead of a file it cannot open.
Running AAC to OGG against the real engine with a real file, ffmpeg wrote 9,482 bytes of OGG in 0.1 seconds, machine otherwise idle. That is one AAC file on one day and not an average, which is why the number is given together with the file that produced it.
The AAC to OGG verdict was reached by ffprobe, meaning the container was actually demultiplexed, recognised under the right name, and carried at least one stream. Which check was used matters, because they do not all prove the same thing, and a status code of 200 proves nothing whatsoever about whether the OGG file has anything inside it.
The same AAC file, sent somewhere else
Other outputs the probe measured out of an AAC file, so the cost of choosing OGG can be read against something. Sizes do not compare across engines, because each family was probed with its own AAC witness file.
AAC to MP3: 24,886 bytes in 0.1 seconds, verified by ffprobe.
AAC to WAV: 268,366 bytes in 0.2 seconds, verified by ffprobe.
AAC to FLAC: 158,116 bytes in 0.1 seconds, verified by ffprobe.
AAC to M4A: 27,924 bytes in 0.2 seconds, verified by ffprobe.
AAC to OPUS: 28,068 bytes in 0.1 seconds, verified by ffprobe.
AAC to WMA: 54,944 bytes in 0.1 seconds, verified by ffprobe.
Other ways into OGG, and what they measured
Among the published routes into OGG, AAC is the third largest output of the 16 measured. The witness files differ, so this ranks the probe run and not your document.
AVI to OGG: 9,164 bytes in 0.1 seconds.
FLAC to OGG: 8,670 bytes in 0.1 seconds.
FLV to OGG: 9,138 bytes in 0.2 seconds.
M4A to OGG: 9,182 bytes in 0.1 seconds.
MKV to OGG: 8,384 bytes in 0.1 seconds.
What we will not pretend about AAC to OGG
An AAC file over 150 MB is refused before the upload finishes rather than after it, so you do not wait for a rejection.
An AAC to OGG run that passes 240 seconds is killed, and the ffmpeg process is killed with it. A run left behind would sit on one of the machine's two cores until somebody noticed.
The AAC file behind the measurement on this page was a 3 second sine wave at 440 hertz, built by ffmpeg for the probe itself. That is why AAC to OGG came out at 0.1 seconds, and it is not what your file will do. The measurement proves the pair works and says almost nothing about how long yours will take.
AAC to OGG costs half a credit per conversion, whatever the length of the AAC. That is the same as an image or a document here, and it is a measurement rather than a gesture: an audio target on this engine is done in under two seconds, where a video target can take minutes.
An AAC longer than 60 minutes is refused before encoding. ffprobe measures the AAC first and answers with a refusal, rather than starting a job the 240 second guard would kill halfway to the OGG.
AAC to OGG waits at the audio door, which is 2 slots wide and gives up after 5 seconds rather than making you wait twenty times the length of the work. Until the 30th there was one door for everything, and a single video transcode starved every audio conversion for its whole duration: an OGG that needed less than a second was answered with a refusal after twenty.
Nothing here reads what is inside the AAC. No transcription, no scene detection, no summary: AAC to OGG is a container and codec operation, and the OGG says exactly what the AAC said, in a different wrapper. The sound is the whole payload.
One AAC file at a time, chosen in the browser. There is nothing else to set up and nothing else on offer.
AAC to OGG: what people ask
What actually converts my AAC file to OGG?
ffmpeg does it, held to a single thread, on a machine we rent and watch. Not a browser trick and not somebody else service: the AAC file is uploaded once, ffmpeg runs once, the OGG comes back, and neither file is kept afterwards.
How long does AAC to OGG take?
The probe measured 0.1 seconds for 9,482 bytes of OGG, on a 3 second file. An audio target scales far better than a video one: three minutes of source through this engine takes under a second, because only the sound is encoded. Past 240 seconds any run is stopped, and an audio one does not get close.
What do I lose going from AAC to OGG?
The one to know about first: Generation loss, and it is the whole story of this pair. AAC threw information away to be small, OGG throws more away on top of what is left, and neither pass can restore what the other removed. Converting the OGG back to AAC afterwards makes it worse a third time, not better.
Will the OGG sound better than the AAC?
No. Nothing in this pass adds information to the AAC, so the OGG is at best an exact carry of what you sent and at worst one more lossy pass over it. Asking for a higher bitrate than the AAC deserved just makes a bigger file of the same recording.
Is AAC to OGG free?
There is a free allowance every month, and one AAC to OGG conversion costs half a credit against it however long the AAC runs. An audio target is charged per conversion and not per minute, because the engine encodes three minutes of sound in well under a second.