[vlc-devel] [PATCH] coreaudio: fix play of uninitialized data (loud CRACK)

[Thomas Guillem]

Superseded by https://mailman.videolan.org/pipermail/vlc-devel/2020-October/138946.html

It was causing an assert in "assert(p_sys->i_out_size == 0)", i_copied need to follow input data.

On Thu, Oct 8, 2020, at 11:21, Alexandre Janniaux wrote:
> Hi,
> 
> LGTM,
> 
> Regards,
> --
> Alexandre Janniaux
> Videolabs
> 
> On Thu, Oct 08, 2020 at 11:08:48AM +0200, Thomas Guillem wrote:
> > When starting deferred (likely), ca_Render() is filling the output
> > buffer with 0s (silence) until the requested start time is reached. When
> > the host time is near the requested start time, the output buffer is
> > partially filled with 0s, and partially filled with valid data.
> >
> > In that particular case, the output buffer offset was not updated
> > causing the valid data to be copied at the beginning of the output
> > buffer, leaving some uninitialized data at the end of the buffer.
> >
> > Fixes #25142
> > ---
> >  modules/audio_output/coreaudio_common.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/modules/audio_output/coreaudio_common.c b/modules/audio_output/coreaudio_common.c
> > index ac4ff53c50c..4761072a296 100644
> > --- a/modules/audio_output/coreaudio_common.c
> > +++ b/modules/audio_output/coreaudio_common.c
> > @@ -129,6 +129,7 @@ ca_Render(audio_output_t *p_aout, uint32_t i_frames, uint64_t i_host_time,
> >            uint8_t *p_output, size_t i_requested)
> >  {
> >      struct aout_sys_common *p_sys = (struct aout_sys_common *) p_aout->sys;
> > +    size_t i_copied = 0;
> >
> >      lock_lock(p_sys);
> >
> > @@ -173,9 +174,10 @@ ca_Render(audio_output_t *p_aout, uint32_t i_frames, uint64_t i_host_time,
> >          const size_t i_silence_bytes =
> >              FramesToBytes(p_sys, UsToFrames(p_sys, i_silence_us));
> >          assert(i_silence_bytes <= i_requested);
> > -        memset(p_output, 0, i_silence_bytes);
> > +        memset(&p_output[i_copied], 0, i_silence_bytes);
> >
> >          i_requested -= i_silence_bytes;
> > +        i_copied += i_silence_bytes;
> >
> >          /* Start the first rendering */
> >      }
> > @@ -183,7 +185,6 @@ ca_Render(audio_output_t *p_aout, uint32_t i_frames, uint64_t i_host_time,
> >      p_sys->i_render_host_time = i_host_time;
> >      p_sys->i_render_frames = i_frames;
> >
> > -    size_t i_copied = 0;
> >      block_t *p_block = p_sys->p_out_chain;
> >      while (p_block != NULL && i_requested != 0)
> >      {
> > --
> > 2.28.0
> >
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