On Wed, 03 May 2023 22:00:37 +0200, Oswald Buddenhagen wrote:
On Wed, May 03, 2023 at 09:32:02PM +0200, Jaroslav Kysela wrote:
On 03. 05. 23 18:10, Takashi Iwai wrote:
The dmix uses the silence_size=boundary as a fill-all operation, and it's a free-wheel mode, so supposedly something was overlooked in your code refactoring.
Could you check it and address quickly? I'd like to fix it before 6.4-rc1 release, so if no fix comes up in a couple of days, I'll have to revert the change for 6.4-rc1.
I would revert this patch.
It seems that this "do silence right after the playback is finished" mechanism is not handled in the updated code (and I overlooked that, too):
no, there is nothing wrong with the code _per se_.
what's happening is that the dmix plugin doesn't update the application pointer, and somehow gets away with it.
that means that it would have never worked with thresholded silencing mode, either, but, well, it uses top-up mode.
Well, the code made just a wrong interpretation for the behavior with silence_size == boundary. This mode is actually a kind of tailored operation for dmix.
In the description of alsa-lib snd_pcm_sw_params_set_silence_size(), you can find it:
/** * \brief Set silence size inside a software configuration container * \param pcm PCM handle * \param params Software configuration container * \param val Silence size in frames (0 for disabled) * \return 0 otherwise a negative error code * * A portion of playback buffer is overwritten with silence when playback * underrun is nearer than silence threshold (see * #snd_pcm_sw_params_set_silence_threshold) * * The special case is when silence size value is equal or greater than * boundary. The unused portion of the ring buffer (initial written samples * are untouched) is filled with silence at start. Later, only just processed * sample area is filled with silence. Note: silence_threshold must be set to zero. */
So, the "top-up" silencing happens only at start, but not after that. In the code path of hw_ptr update, it doesn't check the appl_ptr any longer, but fills the processed area by the hw_ptr update with silence. That's the intended behavior for use cases of free-wheel mode without appl_ptr updates like dmix.
Takashi