[Libav-user] Fwd: How to free an AVBuffer?

[Yurii Monakov]

---------- Пересылаемое сообщение ---------
От: Yurii Monakov <monakov.y at gmail.com>
Дата: Чт, 2 марта 2023 г. в 15:47
Тема: Re: [Libav-user] How to free an AVBuffer?
Кому: Wladislav Artsimovich <ffmpeg at frost.kiwi>


Vlad,

What is the lifetime of your frame? If it is persistent across calls then
you allocate
new side data in every call and ffmpeg simply grows its side data list.

You can use av_frame_new_side_data, copy data to it, send a frame to codec
and
then av_frame_remove_side_data. There is no need to allocate a separate
buffer,
av_frame_new_side_data does this internally.

If you wish to save some allocations, you need to check if side data of a
given
type is already present. If message.Length changes from call to call, you
have to
av_buffer_realloc sideData->buf and fix sideData->data/sideData->size
fields.

Regards,
Yurii


чт, 2 мар. 2023 г. в 07:06, Wladislav Artsimovich <ffmpeg at frost.kiwi>:

> Dear Yurii,
>
> thx for elaborating. Indeed reassigning the pointer was a logical error,
> thx for pointing (hah) it out. I tried using `av_buffer_create()`
> originally, but couldn't find a way of using that function pointer
> callback `av_buffer_default_free()` in C#.
>  From C# pMessageData cannot be freed, but is discarded automatically
> when the fixed{} block ends. I managed to free that MetaDatabuffer and
> the associated memory leak is gone! But not via `av_free()` (which
> didn't work, no error, no freeing), but via `av_buffer_unref()`.
> However, there still remains another memory leak caused by
> `av_frame_new_side_data_from_buf()`
>
> How can I solve that? I tried following
>
> https://chromium.googlesource.com/chromium/third_party/ffmpeg/+/refs/heads/master/libavutil/frame.c#66
> and inserting `ffmpeg.av_buffer_unref(&sideData->buf);
> ffmpeg.av_dict_free(&sideData->metadata); ffmpeg.av_freep(sideData);` at
> different positions and `av_frame_remove_side_data()` at different
> positions, eg. before or after `ffmpeg.av_packet_free(&pPacket);`. The
> Encoder just gracefully stops without error, not processing any further
> frames.
>
> What would be the proper procedure to free that AVFrameSideData?
>
> Here is the full breakdown:
>
> 0 MB memory leaked per 100000 frames:
> fixed (byte* pMessageData = message)
> {
>      //AVBufferRef* MetaDataBuffer =
> ffmpeg.av_buffer_alloc((ulong)message.Length);
>      //System.Buffer.MemoryCopy(pMessageData, MetaDataBuffer->data,
> (ulong)message.Length, (ulong)message.Length);
>      //AVFrameSideData* sideData =
> ffmpeg.av_frame_new_side_data_from_buf(&frame,
> AVFrameSideDataType.AV_FRAME_DATA_SEI_UNREGISTERED, MetaDataBuffer);
>      ffmpeg.avcodec_send_frame(_pCodecContext,
> &frame).ThrowExceptionIfError();
>      //ffmpeg.av_buffer_unref(&MetaDataBuffer);
> }
>
> 62 MB leaked per 100000 frames:
> fixed (byte* pMessageData = message)
> {
>      AVBufferRef* MetaDataBuffer =
> ffmpeg.av_buffer_alloc((ulong)message.Length);
>      System.Buffer.MemoryCopy(pMessageData, MetaDataBuffer->data,
> (ulong)message.Length, (ulong)message.Length);
>      //AVFrameSideData* sideData =
> ffmpeg.av_frame_new_side_data_from_buf(&frame,
> AVFrameSideDataType.AV_FRAME_DATA_SEI_UNREGISTERED, MetaDataBuffer);
>      ffmpeg.avcodec_send_frame(_pCodecContext,
> &frame).ThrowExceptionIfError();
>      //ffmpeg.av_buffer_unref(&MetaDataBuffer);
> }
>
> 0 MB memory leaked per 100000 frames:
> fixed (byte* pMessageData = message)
> {
>      AVBufferRef* MetaDataBuffer =
> ffmpeg.av_buffer_alloc((ulong)message.Length);
>      System.Buffer.MemoryCopy(pMessageData, MetaDataBuffer->data,
> (ulong)message.Length, (ulong)message.Length);
>      //AVFrameSideData* sideData =
> ffmpeg.av_frame_new_side_data_from_buf(&frame,
> AVFrameSideDataType.AV_FRAME_DATA_SEI_UNREGISTERED, MetaDataBuffer);
>      ffmpeg.avcodec_send_frame(_pCodecContext,
> &frame).ThrowExceptionIfError();
>      ffmpeg.av_buffer_unref(&MetaDataBuffer);
> }
>
> 24.5 MB leaked per 100000 frames:
> fixed (byte* pMessageData = message)
> {
>      AVBufferRef* MetaDataBuffer =
> ffmpeg.av_buffer_alloc((ulong)message.Length);
>      System.Buffer.MemoryCopy(pMessageData, MetaDataBuffer->data,
> (ulong)message.Length, (ulong)message.Length);
>      AVFrameSideData* sideData =
> ffmpeg.av_frame_new_side_data_from_buf(&frame,
> AVFrameSideDataType.AV_FRAME_DATA_SEI_UNREGISTERED, MetaDataBuffer);
>      ffmpeg.avcodec_send_frame(_pCodecContext,
> &frame).ThrowExceptionIfError();
>      ffmpeg.av_buffer_unref(&MetaDataBuffer);
> }
>
> Best regards,
>
> Vlad
>
> On 3/2/2023 09:35, Yurii Monakov wrote:
> > av_buffer_alloc allocates buffer of given length (it’s data pointer is
> > not null). And after that you replace that pointer to with your own
> > pointer. So, the first allocation get definitely lost.
> > You should copy pMessageData to MetaDataBuffer->data (and free
> > pMessageData manually) or use av_buffer_create function.
> >
> > Yurii
> >
> > Ср, 1 марта 2023 г. в 06:55, Wladislav Artsimovich <ffmpeg at frost.kiwi>:
> >
> >     Dear FFmpeg and libav users,
> >
> >     I am using FFmpeg.AutoGen in my C# Program to write out frames
> >     encoded
> >     as a h.264 stream and inject per-frame metadata with an
> >     unregistered SEI
> >     Message. It works great, but I have a memory leak, which I don't know
> >     how to address. Source file attached.
> >
> >     Culprit is
> >     ```C#
> >     fixed (byte* pMessageData = message)
> >     {
> >          AVBufferRef* MetaDataBuffer =
> >     ffmpeg.av_buffer_alloc((ulong)message.Length);
> >          MetaDataBuffer->data = pMessageData;
> >          AVFrameSideData* sideData =
> >     ffmpeg.av_frame_new_side_data_from_buf(&frame,
> >     AVFrameSideDataType.AV_FRAME_DATA_SEI_UNREGISTERED, MetaDataBuffer);
> >     }
> >     ```
> >     I create an AVBuffer, as required by
> >     av_frame_new_side_data_from_buf().
> >     But I cannot free it, resulting in a memory leak. I went through
> >     all of
> >     https://ffmpeg.org/doxygen/trunk/group__lavu__buffer.html and
> >     tried out
> >     different av_freep() av_free(), av_buffer_unref() functions, changing
> >     when to free etc. When I think I perform the free correctly, nothing
> >     happens. No error, no freeing just nothing. Clearly I misunderstand
> >     something.
> >     To add insult to injury, the Visual Studio profiler cannot look
> >     inside
> >     the unmanaged memory of libav and reports, that the heap is fine
> >     and not
> >     growing, see attached screenshot.
> >
> >     How and when can I free this memory created allocated by
> >     av_buffer_alloc() in the attached source file?
> >
> >     I asked the same question in the FFmpeg.AutoGen Questions Repo. Some
> >     more context there:
> >     https://github.com/Ruslan-B/FFmpeg.AutoGen.Questions/issues/36
> >
> >     Best regards,
> >
> >     Vlad
> >     _______________________________________________
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> >
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> >
> >
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