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Bit Rate vs. File Size
jjarmak
post May 10 2002, 10:11
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Has a bit rate vs file size study been done? Thanks Jeff
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JohnV
post May 10 2002, 10:17
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Umm, What? Bitrate pretty much dictates the file size.

I'm sorry to ask, but recently there has been very weird questions by you.. so I have to ask.. are you completely serious?? smile.gif Don't be offended if you really are serious.. There has just been quite a lot of weird questions recently by you. smile.gif


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jjarmak
post May 10 2002, 10:39
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Yes John, all of my questions have been serious. If my questions seem strange or unusual, Please understand that I am new and I have a desire to learn. I frequent this board often to aquire new information and stay current on information pertaining to audio. In fact, I probably frequent this board or web site more often then any other and most of the time I have been fairly quiet reading and learning. I'm sorry to anyone who finds a lack of sincerity in my questions. All of my questions have been very sincere and I have established a sense of respect for a few of you out there. Thanks Jeff
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Tinribs
post May 10 2002, 10:46
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I do pretty much the same mate,I visit here umpteen times a day looking for new posts,I read and learn and usually only post a question as a last resort,but dont worry,no one finds your questions insincere,it just takes time to get used to someones 'posting style' and personality. smile.gif
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JohnV
post May 10 2002, 10:59
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Ok Jeff, I apologize.
Please don't be offended. Thanks. smile.gif

Anyway.. there's no need for bitrate-filesize "study" in my opinion, because you do it everytime you encode something. Just take a look at the bitrate.. and file size. smile.gif


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mr1337pants
post May 10 2002, 11:37
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Do you mean file size vs. quality? In my mind, the file size vs. quality issue should be conducted by one's own self to determine how much space they need and how much quality loss is bearable. In some cases, you may wish to leave some headroom (if the space permits it) for future use on some good equipment. I think --alt-preset standard offers excellent filesize/quality, so if you don't have the time to perform testing for your own, I would suggest going with --aps std.

BTW if you need to calculate bitrates -> filesizes, use Audioactive's Bitrate Calculator (it's freeware, scroll all the way down for it).
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jjarmak
post May 10 2002, 11:38
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To give an example of what I was considering when I asked that question was how ogg and mpc compared to one another. Can't they reach close to the same bitrate and yet be different in file sizes? Why did that question seem so strange. Appology accepted. I'm not so easily offended. I just like frequenting this board so often and have already established a feeling of respect for a few folks on here that I really didn't wish to create the feeling of being disrespectful by the questions I ask. Thanks Jeff
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qristus
post May 10 2002, 11:55
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QUOTE
Originally posted by jjarmak
To give an example of what I was considering when I asked that question was how ogg and mpc compared to one another. Can't they reach close to the same bitrate and yet be different in file sizes?
No, the file size is directly correlated to the bitrate, that's why your question seemed so strange smile.gif Because bitrate is "number of bits per second", a 120 second clip at 128kbps will always take up 120 s * 128000b/s = 15360000 bits.

Divide by 8 to get bytes and afterwards by 1024 to get kilobytes, and you'll see that the filesize of a 2-minute clip at 128kbps will always be 1875 kB, or about 1.8 MB - no mater what the codec in use is smile.gif
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verloren
post May 10 2002, 16:08
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Where you can get variations in size is with VBR (variable bit rate) encoding. This became obvious to me using Ogg and comparing it to wma. For Bjork's 'Post' album the ogg files encoded at quality 5.54 (a nominal bit rate of over 170) were smaller on average than wma at 160kbps. This is because the bit rate can drop significantly if there isn't much to encode (silent stretches for example).
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Tinribs
post May 10 2002, 16:44
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I really wouldn't worry too much about which codec and why and get confused,just test a few and if you are happy with the quality then crack on and enjoy the music,if space runs out you can always archive some off to disc to free up space.

Above all its about enjoying your files.smile.gif
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JohnV
post May 11 2002, 02:07
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QUOTE
Originally posted by verloren
Where you can get variations in size is with VBR (variable bit rate) encoding.
No you don't get variations (except small ones from stream format,tags&headers). mpc 160kbps average is the same size as vbr Ogg 160kbps average. Vorbis' nominal bitrate is just nominal.. look at the true average bitrate.

And WMA is a strange format anyway. M$ decided that 1kilobit is 1024 bits, although in reality it's of course 1000 bits. 1kbit=1000 bits.
Although when we talk about bytes, 1kByte=1024 Bytes, but M$ in their infinite wisdom applied this to bits as well when talking about WMA.. rolleyes.gif


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darwyn
post May 11 2002, 08:25
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John V,

That is not quite correct about WMA bitrates. Different encoder do a different amount of "over shot" in the bitrate. I know it is not related to the 1024 (10 bit) formula. Most encodes will be between 640 and 1288 over intended bitrate. This is consistent to all bitrates by the same encoder. That's all I know for simple observations. Perhaps someone else has the real answer. Another odd side effect appears in Winamp. The main display shows a bitrate which appears to be a figure rounded down and then subtracted 1. Such that a file as 128,640 appears at 127 and a file at 129,288 would read 128. Odd....Leave it MS, I guess.

Darwyn
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JohnV
post May 11 2002, 13:02
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QUOTE
Originally posted by darwyn
That is not quite correct about WMA bitrates.
What do you mean?
QUOTE
Most encodes will be between 640 and 1288 over intended bitrate. This is consistent to all bitrates by the same encoder.
What 640 and 1288? 640 and 1288 more bytes in file size?
QUOTE
That's all I know for simple observations. Perhaps someone else has the real answer. Another odd side effect appears in Winamp. The main display shows a bitrate which appears to be a figure rounded down and then subtracted 1. Such that a file as 128,640 appears at 127 and a file at 129,288 would read 128. Odd....Leave it MS, I guess.
Well firstable there's of course small differences between the formats, because of the different bitstream-formats and headers used. Of course there may be few kB differences to the total file size, but nothing remarkable when you encode full length tracks. Second, WinAmp isn't actually the most precise to examine vbr track bitrate/length, with some formats and depending on the case it's clearly off.

I just tested ogg vs mpc. Tweaked so that both encoders show 207.7kbps. File sizes are only 6 _bytes_ off, so practically exactly the same. Same with Lame vbr. Not even a 1kB diference in file size, meaning practically exactly the same file size.


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spoon
post May 11 2002, 15:33
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Possibly because when encoding with WMA v8 you have to ask the codec what bitrates it can do and pick the closest one from an enum, MS possibly have tweaked them slightly higher for reasons best known only to them smile.gif


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tangent
post May 12 2002, 04:22
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I would have thought filesize = bitrate * time
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bryant
post May 12 2002, 06:54
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Just something I wanted to clarify after reading this thread (and some others where I noticed the same possible confusion).

When winamp displays the bitrate, this may or may not be the actual bitrate being consumed, and may or may not be accurate. The reason is that it is the input plugin's responsibility to report the bitrate to winamp, and it can report anything it wants to.

BTW, the same goes for the track length and any tag derived information; winamp has absolutely no idea how to access any of this without its plugins.
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