[FFmpeg-devel] [PATCH v2 3/3] lavc/hevc_mp4toannexb: Exit earlier if there is no nalu payload remaining

[Andriy Gelman]

On Wed, 04. Dec 01:39, Andreas Rheinhardt wrote:
> On Wed, Dec 4, 2019 at 1:04 AM Andriy Gelman <andriy.gelman at gmail.com>
> wrote:
> 
> > From: Andriy Gelman <andriy.gelman at gmail.com>
> >
> > Since the nal unit payload is located after the length prefix, there is
> > no reason to continue reading if there is no nal unit payload remaining.
> > ---
> >  libavcodec/hevc_mp4toannexb_bsf.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/hevc_mp4toannexb_bsf.c
> > b/libavcodec/hevc_mp4toannexb_bsf.c
> > index faf516634b2..c0968b63239 100644
> > --- a/libavcodec/hevc_mp4toannexb_bsf.c
> > +++ b/libavcodec/hevc_mp4toannexb_bsf.c
> > @@ -136,7 +136,7 @@ static int hevc_mp4toannexb_filter(AVBSFContext *ctx,
> > AVPacket *out)
> >
> >      bytestream2_init(&gb, in->data, in->size);
> >
> > -    while (bytestream2_get_bytes_left(&gb)) {
> > +    while (bytestream2_get_bytes_left(&gb) > s->length_size) {
> >
> 
> So if there is some data left, you simply ignore it. It could also be
> argued that this is invalid data.
> (The packet you are dealing with here is padded btw, so you don't need to
> worry about reading beyond the end when reading the size field; which
> actually can't happen anyway, because the safe version of the bytestream
> API is used throughout.)

I suppose it would be invalid data. 

If there are <= s->length_size bytes left then there is no nal unit payload and
there is no point to even parse nalu_size. Plus you avoid calling av_grow_packet() an
extra time.

Thanks,
-- 
Andriy