Re: [FFmpeg-devel] [PATCH] frame durations for framesync

[Paul B Mahol <onemda@gmail.com>]

On 1/30/23, Nicolas George <george@nsup.org> wrote:
> Paul B Mahol (12023-01-27):
>> From b4f835c4ef6e0e0bbe6adef8235381e56f3f91df Mon Sep 17 00:00:00 2001
>> From: Paul B Mahol <onemda@gmail.com>
>> Date: Fri, 27 Jan 2023 23:34:02 +0100
>> Subject: [PATCH 1/4] avfilter/framesync: calculate frame duration too
>>
>> Signed-off-by: Paul B Mahol <onemda@gmail.com>
>> ---
>>  libavfilter/framesync.c | 20 ++++++++++++++++----
>>  libavfilter/framesync.h | 15 +++++++++++++++
>>  2 files changed, 31 insertions(+), 4 deletions(-)
>
> It does not work. For example, with the following filter graph:
>
> testsrc2=r=1/3[a];testsrc2=r=1/5[b];[a][b]vstack
>
> and adding a line of debug at the beginning of process_frame() in
> vf_stack.c, you get:
>
> got event: pts = 0, duration = 3
> got event: pts = 3, duration = 3 ← should be 2
> got event: pts = 5, duration = 5 ← should be 1
> got event: pts = 6, duration = 3 …
> got event: pts = 9, duration = 3
> got event: pts = 10, duration = 5
> got event: pts = 12, duration = 3
> got event: pts = 15, duration = 3
> got event: pts = 18, duration = 3
> got event: pts = 20, duration = 5
>
> I was wrong saying it cannot work, you can compute the duration of the
> new frame without increasing the latency, but you have to duplicate the
> whole frame synchronization logic.
>
> I was against adding the duration field to libavfilter, and this is a
> very good illustration of the reason. The duration field is redundant
> with other information, it takes a lot of code to maintain it, and we
> cannot trust it anyway.

It is not redundant, it describes how much frame lasts.
There is no other way to derive it.

>
> For libavfilter, my advice would be to disregard it entirely. Let us
> just clear it in buffersrc and be done with it.
>

I think you do not understand why frame duration is needed.

> Regards,
>
> --
>   Nicolas George
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