MPEG4AAC is MPEG-4 audio, not video, and implement a _formatid_to_caps() function which tracks a GstCaps to a format ...

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MPEG4AAC is MPEG-4 audio, not video, and implement a _formatid_to_caps() function which tracks a GstCaps to a format name (muxing format etc.), useful for setting caps on demuxers