Re: [FFmpeg-devel] [RFC][PATCH 1/4] avutil/frame: add an internal field to store the size of AVFrame

[James Almer <jamrial@gmail.com>]

On 2/12/2022 9:25 AM, Paul B Mahol wrote:
> On Sat, Feb 12, 2022 at 1:14 AM James Almer <jamrial@gmail.com> wrote:
> 
>> This is unfortunately needed to remove (or reduce the awfulness) of certain
>> modules violating the AVFrame API and using sizeof(AVFrame).
>>
> 
> Which modules?

Anything using wrapped_avframe, so wrapped_avframe decoder and encoder, 
and vapoursynth demuxer, which exports wrapped_avframe packets.

I gave porting the latter into a video source filter some time ago a 
try, which would let us remove the "demuxer", but never sent a patch. I 
can dig it and do that, but it will not change the fact both the 
wrapped_avframe decoder and encoder are still using sizeof(AVFrame).

> 
> 
>> With this, the sizeof(AVFrame) value of the libavutil loaded at runtime
>> can be
>> used instead of the compile time value of whatever library included frame.h
>>
>> Signed-off-by: James Almer <jamrial@gmail.com>
>> ---
>> This is sucks, but at least less so than the current situation.
>>
>> I don't see wrapped_avframe going away anytime soon, so something must be
>> done,
>> and last time i tried to change how the packets are generated my approach
>> was
>> shut down, so here's another attempt.
>>
>>   libavutil/frame.c          |  3 +++
>>   libavutil/frame_internal.h | 33 +++++++++++++++++++++++++++++++++
>>   2 files changed, 36 insertions(+)
>>   create mode 100644 libavutil/frame_internal.h
>>
>> diff --git a/libavutil/frame.c b/libavutil/frame.c
>> index 8997c85e35..a63d2979db 100644
>> --- a/libavutil/frame.c
>> +++ b/libavutil/frame.c
>> @@ -23,6 +23,7 @@
>>   #include "cpu.h"
>>   #include "dict.h"
>>   #include "frame.h"
>> +#include "frame_internal.h"
>>   #include "imgutils.h"
>>   #include "mem.h"
>>   #include "samplefmt.h"
>> @@ -33,6 +34,8 @@
>>                  (frame)->channels == \
>>                  av_get_channel_layout_nb_channels((frame)->channel_layout))
>>
>> +const size_t avpriv_avframe_size = sizeof(AVFrame);
>> +
>>   #if FF_API_COLORSPACE_NAME
>>   const char *av_get_colorspace_name(enum AVColorSpace val)
>>   {
>> diff --git a/libavutil/frame_internal.h b/libavutil/frame_internal.h
>> new file mode 100644
>> index 0000000000..07c246f86a
>> --- /dev/null
>> +++ b/libavutil/frame_internal.h
>> @@ -0,0 +1,33 @@
>> +/*
>> + * This file is part of FFmpeg.
>> + *
>> + * FFmpeg is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU Lesser General Public
>> + * License as published by the Free Software Foundation; either
>> + * version 2.1 of the License, or (at your option) any later version.
>> + *
>> + * FFmpeg is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * Lesser General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU Lesser General Public
>> + * License along with FFmpeg; if not, write to the Free Software
>> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>> 02110-1301 USA
>> + */
>> +
>> +#ifndef AVUTIL_FRAME_INTERNAL_H
>> +#define AVUTIL_FRAME_INTERNAL_H
>> +
>> +#include <stdint.h>
>> +
>> +#include "frame.h"
>> +
>> +/**
>> + * sizeof(AVFrame). If you think you need to use it, then you need to
>> change
>> + * your code so you don't instead.
>> + * Meant for exceptions like wrapped_avframe.
>> + */
>> +extern const size_t avpriv_avframe_size;
>> +
>> +#endif /* AVUTIL_FRAME_INTERNAL_H */
>> --
>> 2.35.1
>>
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