vbf buffer size

[ranvil010]

In tempgnc how do you use VBF buffer size setting so it won't cause and underflow when i multiplex it? I've been trying to do this forever. If yo guys have anygood advice please reply. Thanks

[joe444455555]

I'd love to hear details from an informed person to explain not just what it dose and is for, but what most players are capeable of handeling and the way it affects the encoded video file.

But if you set it to 0,
then click the down arrow once it will change to
0 Automatic
and it will do as is appropriate
40 is common for VCD
112 is common for svcd
224 for DVD
(a kvcd template made "aftermarket" and very well
thought of with 528x480 resolution use 40 for this, don't know why)

[BJ_M]

please don't double post - you have asked this question several times and got answers before - the same answer each time.

[BJ_M]

there are two buffers - one is for the mpeg stream and one is for multiplexing , though there is some interaction ..

the size of the buffer(s) do not effect the quality of your encoded streams - in fact the mpeg stream buffer is not even used by decoders on a PC .

VBV - Video Buffering Verifier

The Video Buffer Verifier (VBV) is a model hypothetical decoder buffer that will not overflow or underflow when fed a conforming MPEG bit stream. Thus, part of the definition of a compliant stream is that it does not cause underflow or overflow of this model buffer. The quantities that MPEG transmits to specify decoder buffer action according to this model are explained fully below. However, decoders do not have to use these quantities, but instead can rely on redundant information provided by time stamps. A thorough explanation is in the section on Buffer Synchronization and Startup .

Operation of the VBV is tied to two transmitted values, vbv_buffer_size_value, the maximum buffer fullness, and vbv_delay, the delay between storing a picture start code in the buffer and starting the decoding of that picture. vbv_buffer_size is transmitted in every sequence header. vbv_delay is transmitted in every picture header. Note that the sequence header and vbv_buffer_size may not be available when tuning to a program in progress. However, proper operation of the decoder buffer can be obtained by use of the System Time Clock and various time stamps and an a priori knowledge of the maximum buffer size that may be required, so that vbv_delay and vbv_buffer size are redundant.

In the ATSC standard A/53 Annex A, the constraint on buffer size is:

maximum video buffer = B = 7995392 bits,

which is specified by transmitting:

vbv_buffer_size_value <= 488 (lower 10 bits of vbv_buffer_size)

vbv_buffer_size_extension = 0 (upper 8 bits of vbv_buffer_size)

where B = 16*1024*vbv_buffer_size.



The ATSC constraint on vbv_delay is

vbv_delay <= 45000



vbv_delay is a 16 bit unsigned integer representing the number of 90kHz clock periods between entering a picture's start code into the buffer and removing and decoding the entire picture.

Compressed video information is inherently variable in nature. This is caused by the, in general, variable content of successive video frames. To store or transmit video at constant bit rate it is therefore necessary to buffer the variable bitstream generated in the encoder in a video buffer (VB) as depicted in Figure 5. The input into the encoder VB is variable over time and the output is a constant bitstream. At the decoder the VB input bitstream is constant and the output used for decoding is variable. MPEG encoders and decoders implement buffers of the same size to avoid reconstruction errors.


A rate control algorithm at the encoder adjusts the quantizer stepsize sz depending on the video content and activity to ensure that the video buffers will never overflow - while at the same time targeting to keep the buffers as full as possible to maximize image quality. In theory overflow of buffers can always be avoided by using a large enough video buffer. However, besides the possibly undesirable costs for the implementation of large buffers, there may be additional disadvantages for applications requiring low-delay between encoder and decoder, such as for the real-time transmission of conversational video. If the encoder bitstream is smoothed using a video buffer to generate a constant bit rate output, a delay is introduced between the encoding process and the time the video can be reconstructed at the decoder. Usually the larger the buffer the larger the delay introduced.


MPEG has defined a minimum video buffer size which needs to be supported by all decoder implementations. This value is identical to the maximum value of the VB size that an encoder can use to generate a bitstream. However, to reduce delay or encoder complexity, it is possible to choose a virtual buffer size value at the encoder smaller than the minimum VB size which needs to be supported by the decoder. This virtual buffer size value is transmitted to the decoder before sending the video bitstream.


Kwag value of 40 for a DVd stream is incorrect and can cause problems on a lot of standalones but would have little effect playing on a PC (as in non)

buffer over/under flows of the mpeg stream can only be determed really by m-probe ...

buffer under/over flows of the multiplexed stream is easier to find but should be rare as most multiplexers use standard values and pack sizes or they should anyway ..

some multiplexors such as manzanita compute this a lot better than other multiplexors but in the case of program streams this is not as critical and in transport streams where it is very very importaint (as is the whole timing issue to prevent jitter) ..

i hope this gives you some explanation so you dont ask this question a 4th time ..

[kwag]

Kwag value of 40 for a DVd stream is incorrect and can cause problems on a lot of standalones but would have little effect playing on a PC (as in non)

Where did you get this information? KDVDs are set to 224, as in standard DVD templates.

-kwag

[BJ_M]

Kwag value of 40 for a DVd stream is incorrect and can cause problems on a lot of standalones but would have little effect playing on a PC (as in non)

:o Where did you get this information? KDVDs are set to 224, as in standard DVD templates.

-kwag

i was quoting joe444455555 post above - i suspect he got a vcd and dvd template mixed up .. 224 is correct or 228 in some encoders .