[FFmpeg-devel] [PATCH 1/4] avcodec/frame: add AV_FRAME_FLAG_LOSSLESS

[Marton Balint]

On Mon, 16 Dec 2024, Anton Khirnov wrote:

> Quoting Marton Balint (2024-12-16 09:47:39)
>>
>>
>> On Mon, 16 Dec 2024, Anton Khirnov wrote:
>>
>>> Quoting Marton Balint (2024-12-15 01:02:42)
>>>> Signed-off-by: Marton Balint <cus at passwd.hu>
>>>> ---
>>>>  doc/APIchanges       | 3 +++
>>>>  libavcodec/version.h | 2 +-
>>>>  libavutil/frame.h    | 4 ++++
>>>>  3 files changed, 8 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/doc/APIchanges b/doc/APIchanges
>>>> index 3a75b803a9..bfba0946d3 100644
>>>> --- a/doc/APIchanges
>>>> +++ b/doc/APIchanges
>>>> @@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07
>>>>
>>>>  API changes, most recent first:
>>>>
>>>> +2024-12-xx - xxxxxxxxxx - lavc 61.27.100 - frame.h
>>>> +  Add AV_FRAME_FLAG_LOSSLESS.
>>>
>>> I feel ambivalent about this. This is really a decoder property, and
>>> attaching it to frames allows it propagate far away to places where it
>>> makes no sense (the same holds for other existing AVFrame fields, but
>>> I'd prefer for them to be removed).
>>
>> The way this flag is set in patch 2 in the series kind of shows why this
>> is a per-frame property, directly originated from the bitstream of codecs
>> supporting both lossy and lossless encoding. The encoder for such codecs
>> is allowed to decide on a frame-by-frame basis if it will use lossy or
>> lossless encoding.
>
> I realize this can change per-frame, my point is that it's a per-frame
> property of the decoding process, not of the decoded frame itself.

As you said yourself, we have similar fields already in AVFrame (keyframe, 
pict_type, decoder_error_flags). I guess we could return those in a struct 
alongside with AVFrame when decoding, but that would complicate stuff in a 
lot of places having to deal with two structs, so I am not sure that it's 
worth doing just for the somewhat "cleaner" AVFrame...

Regards,
Marton