[FFmpeg-user] Why was patch declined: Modified force_key_frames option to accept frame numbers?

[Nick]

Changing the resolution breaks the force_key_frame segmentation with
timestamps. :/
Is there some way to do it?

On 2/16/19 11:22 AM, Nick wrote:
> Thanks for the answer.
> But I want to do the same thing like the person from the mailing list.
> I want that ffmpeg cuts the video in specific segments for DASH with
> variable durations.
> I want to extract this information and use it to cut the video again
> using different qualities.
> I could use the -map command for directly encoding different qualities
> but I want to outsource the workload.
> I want to be sure that everything is aligned.
>
> The one person from the mailing list said:
>
>> In this particular case, you can easily work around the floating point
>> rounding issues, since the rounding behaviour of -force_key_frames is
>> specified: "more precisely at the first frames after each specified time".
>> You just have to make sure your timestamps are rounded down. For example,
>> with 24000/1001 FPS: 4.21 4.25 4.30* 4.34 4.38, you need to write 4.29, not
>> 4.30, but you can also write any value between 4.25425 and the actual
>> 4.295958333. (4.25+4.30)/2 = 4.275 should always work.
> This looks a bit like a workaround to me. Frame numbers look more
> precise for me.
> I do not understand why frame numbers should not be aligned except the
> frame rate is changing.
>
> On 2/16/19 8:52 AM, Gyan wrote:
>>
>> On 16-02-2019 05:03 AM, Nick wrote:
>>> Hi,
>>> why was the "Modified force_key_frames option to accept frame numbers"
>>> (2014) declined?
>>>
>>>> https://ffmpeg.org/pipermail/ffmpeg-devel/2014-November/165167.html
>>> You can even specify frame numbers in the current ffmpeg version using:
>>>> -force_key_frames expr:gte(n,n_forced*96)
>>> Using a framerate of 24 means a keyframe every 4s.
>>> I think it is very useful to have something like
>>>
>>>> /force_key_frames n:0,25,50,75,100/
>> For a regular pattern like that one, you can already use
>>
>>     -force_key_frames expr:not(mod(n,25))
>>
>> Expressions are be evaluated using the interface documented at
>> https://ffmpeg.org/ffmpeg-utils.html#Expression-Evaluation
>>
>>
>> Gyan
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