[FFmpeg-devel] [PATCH]lavf/mxfdec: Export EIA608 Closed Captions by default

[Marton Balint]

On Sun, 17 Feb 2019, Carl Eugen Hoyos wrote:

> 2019-02-17 1:40 GMT+01:00, Marton Balint <cus at passwd.hu>:
>>
>> On Sat, 16 Feb 2019, Carl Eugen Hoyos wrote:
>>>
>>> I am not sure why there is an option to disable Closed Captions export,
>>> but disabling the export by default seems like a bad idea to me.
>>
>> SMPTE 436M can be any kind of ancillary data, not only closed captions.
>> That is why the default behaviour (pass all the data to userspace so a
>> userspace app can parse it properly) makes sense.
>
>> Some applications might depend on this.
>
> Wouldn't it still make more sense to change the default?

Sorry, no. We should not change existing behaviour for this.

> The application that knows it needs the ancillary data, well, knows
> it while the average user who reads the mxf file has no idea that
> there is a subtitle stream and has no idea that FFmpeg can read
> the subtitle stream.
>
> I would bump micro in any case and the option also works fine
> with older FFmpeg versions so I don't really see the issue.

Issue is that you are removing a data stream which was previously 
provided. Also CC extraction in MXF decoder is a hack. It should be 
deprecated after the API will be capable of bitstream filtering between 
different codecs. And the VANC data can be parsed to multiple 
subtitle/data streams. Why eia608 has the perference? Why not teletext, or 
SCTE messages? All in all, it is better to keep hacks under the 
option until we come up with better API.

Regards,
Marton