> I tried setting the bframes to 3 and I got some shakiness back. I can't
> explain why, but 2 bframes seems like the magic number. Is it possible
> that
> bframes starts at 0? 0,1,2 then 2 bframes actually means 3?
>From the firmware api docs.
Name IVTV_API_ASSIGN_GOP_PROPERTIES
Enum 151/0x97
Description
Setup the GOP structure
Param[0]
GOP size
Param[1]
Number of B frames between the I and P frame, plus 1.
For example: IBBPBBPBBPBB --> GOP size: 12, number of B frames: 2+1 = 3
-------------------------------------------------------------------------------
Name IVTV_API_ASSIGN_ASPECT_RATIO
Enum 153/0x99
Description
Sets the encoding aspect ratio. Changes in the aspect ratio take effect
at the start of the next GOP.
Param[0]
'0000' forbidden
'0001' 1:1 square
'0010' 4:3
'0011' 16:9
'0100' 2.21:1
'0101' reserved
....
'1111' reserved
With the ivtv-driver >= 0.8.0 the v4l interface changed a bit from the
ivtv interface.
As you see "Number of B frames between the I and P frame, plus 1" so the
old codec settings has a value of 3 which meant 2 b-frames.
Similar with the aspect.
Why either of these settings should affect the recording smoothness is a
bit of a mystery to me as they where both valid.
Duncan
> On 4/23/07, Justin Wetherell <[EMAIL PROTECTED]> wrote:
>>
>> Maybe it was me but I'll try changing the bframes around again and see
>> what happens.
>>
>> On 4/23/07, Duncan Webb < [EMAIL PROTECTED]> wrote:
>> >
>> > Justin Wetherell wrote:
>> > > After further testing, it seems like it's a combo of aspect and
>> > bframes.
>> > >
>> > > Setting aspect to 2 and bframes to 3, REALLY makes the video jumpy
>> > > Setting aspect to 1 and bframes to 3, KIND of makes the video jumpy
>> > > Setting aspect to 2 and bframes to 2, Still jumpy but not as bad as
>> > line
>> > > above
>> > > Setting aspect to 1 and bframes to 2, very smooth
>> > >
>> > > Lesson learned!
>> >
>> > Thanks Justin you have spotted the problem and the fix is now in svn.
>> >
>> > The video aspect has changed from 2 to 1 for 4x3 and the b-frames are
>> > not offset by 1.
>> >
>> > Having said this it seems strange as the numbers are quite valid. with
>> > b-frames at 3 and the gop size at 12 gives:
>> > IBBBPBBBPBBB|I
>> > the default is 2 giving:
>> > IBBPBBPBBPBB|I
>> >
>> > The aspect ratio was being set to 16x9 instead of 4x3 I would have
>> > expected this to add the wide-screen bit to the recording.
>> >
>> > v4l2-ctl --list-ctrls is the best tool to spot codec setting errors
>> >
>> > Duncan
>> >
>>
>>
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