[FFmpeg-devel] [PATCH] Pass VBV delay to the calling application via ctx

[Måns Rullgård]

Jason Garrett-Glaser <jason at x264.com> writes:

> On Tue, Feb 8, 2011 at 6:39 AM, Christophe Massiot <cmassiot at freebox.fr> wrote:
>> On Tue, Feb 08, 2011, M?ns Rullg?rd wrote:
>>
>>> > + ? ?/**
>>> > + ? ? * VBV delay coded in the last frame (in seconds).
>>> > + ? ? * Used for compliant TS muxing.
>>> > + ? ? * - encoding: Set by libavcodec.
>>> > + ? ? * - decoding: unused.
>>> > + ? ? */
>>> > + ? ?double vbv_delay;
>>>
>>> I don't like floating-point. ?Could this be expressed in some other
>>> units instead?
>>
>> Sure but I have difficulties choosing one. MPEG has two natural clock
>> frequencies : 90 kHz and 27 MHz. VBV delay in MPEG-1/2 is actually based
>> on the 90 kHz clock.
>>
>> However, probably other codecs have other clocks, maybe more precise
>> than 90 kHz, so if we want to generalize this principle we need a more
>> generic clock source. VLC would be perfectly happy with microseconds but
>> you could equally choose nanoseconds or anything else that fits in an
>> integer...
>>
>> x264 solved this dilemma by using "double". Not sure whether 27 MHz
>> would be acceptable for other codecs. Opinions welcomed here...
>
> Infinite precision (that is, "guaranteed not to have rounding error")
> is probably not useful externally: as long as the internal clock is
> kept in infinite precision, the exported information can be marginally
> imprecise.  Double should work fine.

It probably will, but it still makes me uneasy.

-- 
M?ns Rullg?rd
mans at mansr.com