[FFmpeg-devel] [PATCH 4/4] avformat/mxfenc: add some missing content package rates

[Marton Balint]

On Mon, 2 Mar 2020, Baptiste Coudurier wrote:

> Hey guys,
>
>
>> On Mar 2, 2020, at 12:57 PM, Marton Balint <cus at passwd.hu> wrote:
>> 
>> 
>> 
>> On Mon, 2 Mar 2020, Tomas Härdin wrote:
>> 
>>> fre 2020-02-28 klockan 10:30 +0100 skrev Marton Balint:
>>>> On Fri, 28 Feb 2020, Carl Eugen Hoyos wrote:
>>>> > Am Fr., 28. Feb. 2020 um 01:38 Uhr schrieb Marton Balint <cus at passwd.hu>:
>>>> > > Fixes ticket #8523.
>>>> > > > > Signed-off-by: Marton Balint <cus at passwd.hu>
>>>> > > ---
>>>> > >  libavformat/mxf.c | 13 +++++++++++++
>>>> > >  1 file changed, 13 insertions(+)
>>>> > > > > diff --git a/libavformat/mxf.c b/libavformat/mxf.c
>>>> > > index 14056647c5..987410258a 100644
>>>> > > --- a/libavformat/mxf.c
>>>> > > +++ b/libavformat/mxf.c
>>>> > > @@ -135,10 +135,23 @@ static const MXFContentPackageRate mxf_content_package_rates[] = {
>>>> > >      {  2, { 1,    24    } },
>>>> > >      {  3, { 1001, 24000 } },
>>>> > >      {  4, { 1,    25    } },
>>>> > > +    {  6, { 1,    30    } },
>>>> > >      {  7, { 1001, 30000 } },
>>>> > > +    {  8, { 1   , 48    } },
>>>> > > +    {  9, { 1001, 48000 } },
>>>> > >      { 10, { 1,    50    } },
>>>> > >      { 12, { 1,    60    } },
>>>> > >      { 13, { 1001, 60000 } },
>>>> > > +    { 14, { 1,    72    } },
>>>> > > +    { 15, { 1001, 72000 } },
>>>> > > +    { 16, { 1,    75    } },
>>>> > > +    { 18, { 1,    90    } },
>>>> > > +    { 19, { 1001, 90000 } },
>>>> > > +    { 20, { 1,    96    } },
>>>> > > +    { 21, { 1001, 96000 } },
>>>> > > +    { 22, { 1,    100   } },
>>>> > > +    { 24, { 1,    120   } },
>>>> > > +    { 25, { 1001, 120000} },
>>>> > > Are these still the only supported frame rates?
>>>> These are the *package* rates that SMPTE 326M defines (technically it defines the /1.001 version of 25, 50, 75 and 100 fps, but those are not used).
>>> 
>>> For the record, this is section 7.2 Content package rate in SMPTE 326M-
>>> 2000. What is not initially obvious is that mxf_content_package_rates-
>>>> rate is bits b5..b0. A comment about this would be nice, I don't like
>>> magical tables in the MXF codebase not being justified by references :)
>>> 
>>> You could technically have 25/1.001, 50/1.001, 75/1.001 and 100/1.001
>>> too. But it's probably wise not to do that.
>> 
>> I am not sure, maybe we should add all possible values, even if they are uncommon. After all I found out that for example 50/1.001 is actually supported for mkvmerge:
>
> It seems like if we were to do that, we would open the door to allowing essences that don’t support the package rate and we should definitely NOT do that.

I am not sure I understand, there are two different things to consider:

1) support every frame rate which can be exactly represented by a package 
rate as defined in SMPTE 326M, even uncommon ones like 50/1.001.

2) support all frame rates and write 0 (undefined) as the package rate 
for frame rates which cannot be exactly represented

You are voting against 2), right? 1) should not cause any "compatibility" 
issues as far as I see.

Thanks,
Marton