| Author |
Message |
Guest
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 Posted:
Tue Jul 26, 2005 4:42 am Post subject:
bitrate from frame size |
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hello,
Given a MPEG2 video stream, how can i find the bit rate. The indivisual
frame sizes of a given frame is known. We dont have access to the total
number of frames nor the video file size.
If there any specific formula.
One way that i found by trial & error was
video_file_size * 8 = 20 * average_bit_rate
but this equation requires the knowledge of full video file size or the
total number of frames.
-mic
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erik
Guest
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| Posted:
Tue Jul 26, 2005 12:29 pm Post subject:
Re: bitrate from frame size |
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<micromysore@gmail.com> wrote in message
news:1122339660.124307.57980@g14g2000cwa.googlegroups.com...
| Quote: | hello,
Given a MPEG2 video stream, how can i find the bit rate. The
indivisual
frame sizes of a given frame is known. We dont have access to the
total
number of frames nor the video file size.
If there any specific formula.
One way that i found by trial & error was
video_file_size * 8 = 20 * average_bit_rate
but this equation requires the knowledge of full video file size or
the
total number of frames.
-mic
|
You can take just a part of the file and calculate its average
bitrate. If CBR is used, the result will be OK, with VBR, calculated
bitrate may differ, depending on the contents of the material.
Basicaly you need to know the total size and length (duration), that's
how average bitrate is defined.
http://www.videohelp.com/calc.htm
Manually calculate the bitrate
The basic bitrate formula is
(Size - (Audio x Length )) / Length = Video bitrate
L = Lenght of the whole movie in seconds
S = Size you like to use in KB (note 700 MB x 1024° = 716 800 KB)
A = Audio bitrate in KB/s (note 224 kbit/s = 224 / 8° = 28 KB/s)
V = Video bitrate in KB/s, to get kbit/s multiply with 8°.
°8 bit = 1 byte.
°1024 = 1 kilo in the computer world.
Example
90 minutes video, L = 90 x 60 = 5 400 seconds
700 MB CD but be sure that if fits use a bit lower like 695 MB, S =
695 x 1024 = 711 680 KB
Audio bitrate, A = 224 kbit/s / 8 = 28 KB/s
(711 680 - (5400 x 28) ) / 5400 = 104 KB/s x 8° = 830 kbit/s. |
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newbie
Guest
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| Posted:
Tue Jul 26, 2005 6:34 pm Post subject:
Re: bitrate from frame size |
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You can use a program like AVICODEC. Or you can open the file
in Virtualdub-MPEG or Virtualdub-Mod and read the "file information".
I just add these programs to the "Send To" context menu list so I can
find out info about videos with just two mouse clicks.
On 25 Jul 2005 18:01:00 -0700, micromysore@gmail.com wrote:
| Quote: | hello,
Given a MPEG2 video stream, how can i find the bit rate. The indivisual
frame sizes of a given frame is known. We dont have access to the total
number of frames nor the video file size.
If there any specific formula.
One way that i found by trial & error was
video_file_size * 8 = 20 * average_bit_rate
but this equation requires the knowledge of full video file size or the
total number of frames.
-mic |
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| Back to top |
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Guest
|
| Posted:
Wed Jul 27, 2005 1:12 am Post subject:
Re: bitrate from frame size |
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what i am trying to do here is ..
I have written a program, which has a buffer size resonable enuf to
accomodate a GOP (if required will create another buffer to hold the
frame sizes, of required length). the video is a never ending stream.
So, there is no info on the total number of seconds nor the total file
size of the video. I know during encoding, there is something called
"rate-control" which kind of controls the output-bitrate. What I am
trying to understand is, how is that computed ? The ONLY info I have is
the indivisual frame sizes in bytes. With this info, how do i compute
the bitrate ?
-mic |
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Jan Panteltje
Guest
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| Posted:
Wed Jul 27, 2005 1:20 am Post subject:
Re: bitrate from frame size |
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On a sunny day (26 Jul 2005 13:12:36 -0700) it happened micromysore@gmail.com
wrote in <1122408756.283291.175620@g47g2000cwa.googlegroups.com>:
| Quote: | what i am trying to do here is ..
I have written a program, which has a buffer size resonable enuf to
accomodate a GOP (if required will create another buffer to hold the
frame sizes, of required length). the video is a never ending stream.
So, there is no info on the total number of seconds nor the total file
size of the video. I know during encoding, there is something called
"rate-control" which kind of controls the output-bitrate. What I am
trying to understand is, how is that computed ? The ONLY info I have is
the indivisual frame sizes in bytes. With this info, how do i compute
the bitrate ?
If you measure the number of output bits during one second you have the |
bitrate. |
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