About the maximum bit rate of the audio lossy compression format
According to him
standard [MP3], the maximum bit rate is set to 320 kbps.
MP3 compresses audio into units called frames. A frame is determined to have 1152 samples, and if the sample rate is 44.1 kHz, a frame is 1/44 100 x 1152 ≒ about 0.026 seconds.
MP3 can take any of the 14 default types of bit rate values (32,40,48,56,64,80,96,112,128,160,192,224,256,320kbps for MPEG1) for each frame, and all frames have the same bit rate. It’s called CBR (Fixed Bit Rate), and what’s different for each frame is called VBR (Variable Bit Rate).
Therefore, the maximum bit rate is 320 kbps for all frames in CBR and the highest sound quality is achieved.
Also, the lame encoder can create MP3s of up to 640kbps for CBR only by its own extension outside of the standard (although it should not be called MP3 strictly because it is not standard). Of course, since it is out of the standard, only a small part of the software can be played. With MP3s, which are the best selling point for their versatility, messing them up may not be a good idea.
[AAC]
The upper limit of the standard is
264.6 x 2 = 529.2 kbps (in the case of 44.1 kHz 2 channels)
288 x 2 = 576 kbps (48 kHz) for 2 channels)
However, it appears that the actual encoders are “up to 256 kbps per channel” (512 kbps for 2 channels).
However, there are some strange programs for beginners like iTunes, x-app, Media Go, etc. which set the upper limit of the AAC bit rate at 320 kbps. Because of this, it seems that there are quite a few beginners who think that AAC has a maximum of 320 kbps like MP3 ^^; well maybe it’s just MP3. ･ ･ ･ Well actually 320 kbps is enough.
[Ogg Vorbis]
It seems that the upper limit is not set in particular by the standard, but in the current general encoder, it appears to be “up to 256 kbps per channel” (512 kbps for 2 channels).
[WMA] It
very difficult to understand, and personally I don’t want to use it at all, so I haven’t researched it in detail, so it may be wrong …
Microsoft’s WMA encoder has a profile (like a preset), and it basically converts according to it, but the variety of profiles is kind of weird. The profile commonly used in the WMA9.2 Std format appears to be a mysterious specification offering up to 320 kbps at 44.1 kHz, but only up to 192 kbps at 48 kHz.
Perhaps because of this, some software unifies both up to a maximum of 192kbps, and there is a section where many people think that it is a WMA standard.
320 kbps (for 44.1 kHz, 16 bit, 2 channels), 192 kbps (for 48 kHz, 16 bit, 2 channels) for normal WMA 9.2 format, 440 kbps (for 44.1 kHz, 24 bit, 2 channels ), 256 kbps (44.1 kHz, for WMA10Pro format) 16 bits, 2 channels) seems to be the upper limit (at least we could build it up to that point). Even CBR looks like this, so I’m not sure what the maximum bit rate of each frame is for VBR (which has 1-step and 2-step encoding) so I don’t know the details.
Some conversion tools that support multiple formats use FFmpeg for WMA encoding. The WMA encoding feature included in FFmpeg is based on the old WMA8, so it may be different from the above. I do not want to look for it and it is better not to use it.
