aac to jpg conversion is not doable directly, that is via file to file conversion, simply due the fact of completely different types AAC and JPG are. The first one is audio content, the other graphics file, often picture or photograph.
Despite many online converters that do advertise this conversion as supported, it is unlikely that works.
The only thing that can be done sometimes, is recovery of a thumbnail preview (of album art for example) from multimedia file, but that is the case of container formats, such as MPEG-4 and not audio track like AAC format in this case. In such case the picture is placed together with the .aac file inside MP4 file and you have to use special software (audio editor, metadata tagging software) to disect the container.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
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