[FFmpeg-devel] [PATCH v2 5/5] fftools/ffmpeg: support applying container level cropping

[James Almer]

On 7/27/2023 8:13 AM, Anton Khirnov wrote:
> Quoting Tomas Härdin (2023-07-26)
>> tis 2023-07-25 klockan 14:09 -0300 skrev James Almer:
>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>> ---
>>> Now inserting a filter into the graph.
>>
>> This looks useful for MXF
>>
>>> +    { "apply_cropping",   HAS_ARG | OPT_BOOL | OPT_SPEC |
>>> +                          OPT_EXPERT |
>>> OPT_INPUT,                                { .off =
>>> OFFSET(apply_cropping) },
>>> +        "Apply frame cropping instead of exporting it" },
>>
>> Hm. Can this be applied automatically for ffplay? When transcoding I
>> expect the typical use case is to not crop and to carry the metadata
>> over.
> 
> Why? We do apply decoder cropping by default. There's also no guarantee
> that your container will be able to write it, so it seems better to
> apply it by default.

I agree. In a transcoding scenario you want to apply the container level 
cropping since it's defining a subrectangle with the actual content 
meant for display, so why force the encoder handle pixels that were 
meant to be discarded to being with, potentially ruining encoding 
quality for neighboring pixels?

For codec copy scenarios though, the side data is going to be copied, so 
Tomas' idea of having muxers report they support writing it is good 
either way.