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

[Marton Balint]

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:

https://gitlab.com/mbunkus/mkvtoolnix/-/commit/1a350a9573e4f895223e7ab10f7d491440abaf62

Regards,
Marton

>
>> > How do archivists store low-fps film in mxf?
>> 
>> I don't know. One can write an undefined package rate into the file, or 
>> the frame rate can may be different from package rate. You can put almost 
>> anything into MXF, the only problem is that it will not be widely 
>> supported or readable.
>
> Like Marton says, MXF allows anything. In practice everyone uses a
> small set of profiles of MXF. No one attempts to support all of MXF,
> that way lies madness.
>
> /Tomas
>
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