[FFmpeg-devel] [PATCH] pulse: set default frame_size to 4608

[Federico Simoncelli]

On Fri, Jan 3, 2014 at 3:44 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Fri, Jan 03, 2014 at 01:21:41AM +0100, Federico Simoncelli wrote:
>> On Thu, Jan 2, 2014 at 11:26 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> > On Thu, Jan 02, 2014 at 04:36:45PM +0100, Federico Simoncelli wrote:
>> >> Given the current defaults (channels = 2, sample_rate = 48000) the
>> >> frame_size is changed to 4608 in order to obtain whole numbers for
>> >> frame_duration (both 16 and 24 bits_per_sample).
>> >>
>> >>  frame_duration = (frame_size * 1000000 * 8) /
>> >>                   (sample_rate * channels * bits_per_sample)
>> >>
>> >> A message has been added to warn the user when the frame duration
>> >> is not an integer.
>> >
>> > the timebase should be changed to a multiple of the sample rate
>> > see the avpriv_set_pts_info() call
>> > that avoids the problem of the durations being not exactly
>> > representable
>>
>> If I understand correctly what you're suggesting is:
>>
>> avpriv_set_pts_info(st, 64, 1, pd->sample_rate);
>
> yes
>
>> and it will generate non-representable timebases:
>>
>> 1/48 = .020833...
>> 1/44.1 = .0226757
>
> rational numbers are quite representable, and really 1/1000000 is
> a rational number in no way different than 1/48 or 1/48000 is
> also if you dont like fractions you can just change the base of
> your representation
>
> ...
>
> so really the non representability is just an artifact of humans
> having 10 fingers

Yes, that's clear, what I meant is that there was 10-fingered code
around somewhere since I was getting pts warnings after changing the
timebase.
Instead I pinpointed this to be something related to the mp3 encoder
(I don't know what yet).

In fact for some reason it generates a (imo) weird initial frame:

frame_pts = 1105, frame_ts = 0.023021, base_ts = 0.000021
frame_pts = 1152, frame_ts = 0.024000, base_ts = 0.000021
frame_pts = 2304, frame_ts = 0.048000, base_ts = 0.000021
frame_pts = 3456, frame_ts = 0.072000, base_ts = 0.000021
...

something that the aac encoder is not doing:

frame_pts = 1024, frame_ts = 0.021333, base_ts = 0.000021
frame_pts = 2048, frame_ts = 0.042667, base_ts = 0.000021
frame_pts = 3072, frame_ts = 0.064000, base_ts = 0.000021
frame_pts = 4096, frame_ts = 0.085333, base_ts = 0.000021

-- 
Federico