VBV buffer size

[montreal.simo]

Hello,

I want to set the VBV buffer size at the x264 encoder side. usually with ffmpeg, there is vbv-bufsize and vbv-maxrate options to enable single-frame vbv support to cap frames to the same maximum size.

how can i do it with Gstreamer? I find the option vbv-buf-capacity but i dont know how to activate single-frame vbv support?

thank you for your help :)

[kieranrk]

Make the buffer duration close to one frame in length and x264 will figure it out.

[montreal.simo]

is exactly what I do, with frame rate of 25fps i configure vbv-buf-capacity = 40ms. but how this configure the frames to the same maximum size ? or i have to fix quality (e,g pass=qual, quantizer= 22) ?

[kieranrk]

Your buffer size is in bits. You need to choose one in your case such that bufsize/maxrate = 40ms.

[montreal.simo]

no, the vbv-buf-capacity define the size of the vbv buffer in milliseconds. 40ms is one frame, but this not configure the size of the frame ?

[kieranrk]

no, the vbv-buf-capacity define the size of the vbv buffer in milliseconds. 40ms is one frame, but this not configure the size of the frame ?

You are wrong.

[montreal.simo]

can you plz explain more !

thx

[Guest]

If you are interested in the absolute size of the bit buffer to be sure it will contain your IDR/I frames, then remember that size is (vbv_rate * time), so when you specify the time you thereby set the size as well, or vice versa.

[montreal.simo]

If you are interested in the absolute size of the bit buffer to be sure it will contain your I frames, then remember that size is (bitrate * time), so when you specify the time you thereby set the size as well.

i use intra-refresh instead IDR-frames, so I frames are disabled.

the size=bitrate*time. so i have to specify the bitrate ?

thx

[kieranrk]

You need to make sure your buffer size is one frame in size. You do this by making the time the buffer takes to fill equal to the duration of one frame. This is done by setting vbv-bufsize/vbv-maxrate to 0.04 seconds. So example 25kbit bufsize and 1000kbit/s vbv-maxrate. That is how you get single-frame vbv.

[montreal.simo]

You need to make sure your buffer size is one frame in size. You do this by making the time the buffer takes to fill equal to the duration of one frame. This is done by setting vbv-bufsize/vbv-maxrate to 0.04 seconds. So example 25kbit bufsize and 1000kbit/s vbv-maxrate. That is how you get single-frame vbv.

thank you for the explanation.

I understand perfectly what you are saying. but, in Gstreamer the options vbv-bufsize and vbv-maxrate does not exist. the only option available is vbv-buf-capacity which defines the buffer size in milliseconds.and this is not enough to define the size in bits.

where i need another option to do this.

[kieranrk]

thank you for the explanation.

I understand perfectly what you are saying. but, in Gstreamer the options vbv-bufsize and vbv-maxrate does not exist. the only option available is vbv-buf-capacity which defines the buffer size in milliseconds.and this is not enough to define the size in bits.

where i need another option to do this.

You should be able to set the vbv-buf-capacity to 40ms and set a bitrate then I would imagine. x264 should do to the right thing I would imagine.

[montreal.simo]

yep, i agree with you.

thanks for your help