[FFmpeg-devel] [PATCHv2] avcodec/utils: do not reallocate packet buffer for AV_CODEC_ID_WRAPPED_AVFRAME

[wm4]

On Sun, 19 Feb 2017 14:49:34 +0100
Hendrik Leppkes <h.leppkes at gmail.com> wrote:

> On Sun, Feb 19, 2017 at 2:41 PM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Sun, 19 Feb 2017 14:35:42 +0100
> > Marton Balint <cus at passwd.hu> wrote:
> >  
> >> Reallocating a wrapped avframe invalidates internal pointers, such as extended
> >> data.
> >>
> >> FFmpeg has another way of passing AVFrames to muxers, but it seems the API
> >> (av_write_uncoded_frame) is not implemented in the ffmpeg CLI yet.
> >>
> >> Signed-off-by: Marton Balint <cus at passwd.hu>
> >> ---
> >>  libavcodec/utils.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> >> index f4085bf..184821a 100644
> >> --- a/libavcodec/utils.c
> >> +++ b/libavcodec/utils.c
> >> @@ -1820,7 +1820,7 @@ int attribute_align_arg avcodec_encode_audio2(AVCodecContext *avctx,
> >>      AVFrame *padded_frame = NULL;
> >>      int ret;
> >>      AVPacket user_pkt = *avpkt;
> >> -    int needs_realloc = !user_pkt.data;
> >> +    int needs_realloc = !user_pkt.data && avctx->codec_id != AV_CODEC_ID_WRAPPED_AVFRAME;
> >>
> >>      *got_packet_ptr = 0;
> >>
> >> @@ -1964,7 +1964,7 @@ int attribute_align_arg avcodec_encode_video2(AVCodecContext *avctx,
> >>  {
> >>      int ret;
> >>      AVPacket user_pkt = *avpkt;
> >> -    int needs_realloc = !user_pkt.data;
> >> +    int needs_realloc = !user_pkt.data && avctx->codec_id != AV_CODEC_ID_WRAPPED_AVFRAME;
> >>
> >>      *got_packet_ptr = 0;
> >>  
> >
> > I don't understand this logic in the first place. If nothing was
> > encoded (!ret), and avpkt->data is set (why is it set?), then the
> > AVPacket.buf is realllocated (why?) to the packet size (why???) - how
> > does it make sense?  
> 
> ret = 0 indicates successfull encode, ie. not an error code. What
> result code did you expect?

Somehow I expected it to return the number of bytes encoded or
something, but of course that's nonsense. (Maybe I was confused that
the check was !ret and not ret>=0.)

> AFAIK the realloc is performed to shrink over-sized pre-allocated
> packets down and save memory.

OK, so something fishy. Can't it just skip reallocation if the buffer
is already minimally sized (which wrapped_avframe.c already does)?