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

[Marvin Scholz]

Tested this patch and it seems to fix the issue for me.
A bit hard to tell due to how hard it is to reproduce but I
tried ~40 times now and the there never was a crack at the
beginning with the patch.
While without it, it reproduce after ~10 tries.

On 8 Oct 2020, at 12:31, 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 | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/modules/audio_output/coreaudio_common.c 
> b/modules/audio_output/coreaudio_common.c
> index ac4ff53c50c..fd8ee7279d6 100644
> --- a/modules/audio_output/coreaudio_common.c
> +++ b/modules/audio_output/coreaudio_common.c
> @@ -176,6 +176,7 @@ ca_Render(audio_output_t *p_aout, uint32_t 
> i_frames, uint64_t i_host_time,
>          memset(p_output, 0, i_silence_bytes);
>
>          i_requested -= i_silence_bytes;
> +        p_output += i_silence_bytes;
>
>          /* Start the first rendering */
>      }
> @@ -188,9 +189,11 @@ ca_Render(audio_output_t *p_aout, uint32_t 
> i_frames, uint64_t i_host_time,
>      while (p_block != NULL && i_requested != 0)
>      {
>          size_t i_tocopy = __MIN(i_requested, p_block->i_buffer);
> -        memcpy(&p_output[i_copied], p_block->p_buffer, i_tocopy);
> +        memcpy(p_output, p_block->p_buffer, i_tocopy);
>          i_requested -= i_tocopy;
>          i_copied += i_tocopy;
> +        p_output += i_tocopy;
> +
>          if (i_tocopy == p_block->i_buffer)
>          {
>              block_t *p_release = p_block;
> @@ -215,7 +218,7 @@ ca_Render(audio_output_t *p_aout, uint32_t 
> i_frames, uint64_t i_host_time,
>      {
>          assert(p_sys->i_out_size == 0);
>          p_sys->i_underrun_size += i_requested;
> -        memset(&p_output[i_copied], 0, i_requested);
> +        memset(p_output, 0, i_requested);
>      }
>
>      lock_unlock(p_sys);
> -- 
> 2.28.0
>
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