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

[Alexandre Janniaux]

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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