[FFmpeg-devel] [PATCH] avfilter: do not write to unwritable frame

[wm4]

On Fri, 27 Jan 2017 22:04:50 +0700
Muhammad Faiz <mfcc64 at gmail.com> wrote:

> On 1/27/17, wm4 <nfxjfg at googlemail.com> wrote:
> > On Fri, 27 Jan 2017 18:42:03 +0700
> > Muhammad Faiz <mfcc64 at gmail.com> wrote:
> >  
> >> affect filters that set partial_buf_size
> >> test-case
> >> ffplay -i lavfi 'aevalsrc=sin(1000*t*t), aformat=sample_fmts=fltp, asplit
> >> [a][b];
> >> [a] firequalizer=fixed=on, showcqt=s=1280x360 [a1];
> >> [b] firequalizer=fixed=on, showcqt=s=1280x360 [b1];
> >> [a1][b1] vstack'
> >>
> >> Signed-off-by: Muhammad Faiz <mfcc64 at gmail.com>
> >> ---
> >>  libavfilter/avfilter.c | 17 +++++++++++++++++
> >>  1 file changed, 17 insertions(+)
> >>
> >> diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
> >> index c12d491..7e7e83c 100644
> >> --- a/libavfilter/avfilter.c
> >> +++ b/libavfilter/avfilter.c
> >> @@ -1235,6 +1235,23 @@ static int take_samples(AVFilterLink *link,
> >> unsigned min, unsigned max,
> >>          frame = ff_framequeue_peek(&link->fifo, 0);
> >>          av_samples_copy(buf->extended_data, frame->extended_data, p, 0,
> >> n,
> >>                          link->channels, link->format);
> >> +
> >> +        if (!av_frame_is_writable(frame)) {
> >> +            AVFrame *new = ff_get_audio_buffer(link, frame->nb_samples);
> >> +            if (!new)
> >> +                return AVERROR(ENOMEM);
> >> +            ret = av_frame_copy_props(new, frame);
> >> +            if (ret < 0)
> >> +                return ret;
> >> +            av_samples_copy(new->extended_data, frame->extended_data,
> >> +                            0, 0, frame->nb_samples,
> >> +                            av_frame_get_channels(frame),
> >> +                            frame->format);
> >> +            av_frame_unref(frame);
> >> +            av_frame_move_ref(frame, new);
> >> +            av_frame_free(&new);
> >> +        }
> >> +
> >>          frame->nb_samples -= n;
> >>          av_samples_copy(frame->extended_data, frame->extended_data, 0, n,
> >>                          frame->nb_samples, link->channels, link->format);  
> >
> > There's a function that does this automatically:
> > av_frame_make_writable()  
> 
> OK, I have known this.
> 
> >
> > Might not be fully equivalent though due to ff_get_audio_buffer()  
> 
> If it is permitted to not use ff_get_audio_buffer(), I will use
> av_frame_make_writable().

I don't know about the details. Actually it looks like the ff_ function
does something non-trivial (like using a buffer pool or allocating a
buffer from the next filter).

So it looks like your code is actually slightly more correct than a
solution using av_frame_make_writable(). Although it's sad that most of
the av_frame_make_writable() function has to be sort-of duplicated.

So, patch is ok by me. Sorry for the additional confusion.

(Maybe av_frame_copy() could be used instead of av_samples_copy().)