Re: [mpg123-users] mpg123_read() (Error reading the stream. (code 18))

[Leonard B. <leo...@gm...>]

Thanks!

> On 26/02/2021, at 10:02 PM, Thomas Orgis <tho...@or...> wrote:
> 
> Am Fri, 26 Feb 2021 21:34:31 +1300
> schrieb Leonard Bocock <leo...@gm...>: 
> 
>> (1) The use of fread()
> 
> I didn't follow quite what was the issue here, but I am joyous that you
> worked it out!
> 
>> (2) The small buffer size from mpg123_outblock(mh) which is
>> inadequate for ALSA (a small buffer causes ALSA to play with jitter)
> 
> I don't quite understand this. You configure the buffers ALSA uses,
> independent of the chunks to write. See
> 
> 	http://scm.orgis.org/view/mpg123/trunk/src/libout123/modules/alsa.c?view=markup
> ,
> which you could use via libout123, too. In essence:
> 
> 34            #define BUFFER_LENGTH (ao->device_buffer > 0. ? ao->device_buffer : 0.2)
> 116            buffer_size = rate * BUFFER_LENGTH;
> 117 	        if (snd_pcm_hw_params_set_buffer_size_near(pcm, hw, &buffer_size) < 0) {
> 118 	                if(!AOQUIET) error("initialize_device(): cannot set buffer size");
> 119 	                return -1;
> 120 	        }
> 121 	        debug1("buffer_size=%lu", (unsigned long)buffer_size);
> 122 	        period_size = buffer_size / 3; /* 3 periods is so much more common. */
> 123 	        if (snd_pcm_hw_params_set_period_size_near(pcm, hw, &period_size, NULL) < 0) {
> 124 	                if(!AOQUIET) error("initialize_device(): cannot set period size");
> 125 	                return -1;
> 126 	        }
> 127 	        debug1("period_size=%lu", (unsigned long)period_size);
> 128 	        if (snd_pcm_hw_params(pcm, hw) < 0) {
> 129 	                if(!AOQUIET) error("initialize_device(): cannot set hw params");
> 130 	                return -1;
> 131 	        }
> 132 	
> 
> Important was that one, which I only realized quite recently:
> 
> 138 	        /* Start playing once we got at least full period ... this is not default? */
> 139 	        if (snd_pcm_sw_params_set_start_threshold(pcm, sw, buffer_size/2) < 0) {
> 140 	                if(!AOQUIET) error("initialize_device(): cannot set start threshold");
> 141 	                return -1;
> 142 	        }
> 
> And then the writing with whatever chunk size:
> 
> 230             frames = snd_pcm_bytes_to_frames(pcm, bytes);
> 231 	        while
> 232 	        ( /* Try to write, recover if error, try again if recovery successful. */
> 233 	                (written = snd_pcm_writei(pcm, buf, frames)) < 0
> 234 	                && snd_pcm_recover(pcm, (int)written, 0) == 0
> 235 	        )
> 236 	        {
> 237 	                debug2("recovered from alsa issue %i while trying to write %lu frames", (int)written, (unsigned long)frames);
> 238 	        }
> 
> 
> Of course, you could also do it like
> 
> 	http://scm.orgis.org/view/mpg123/trunk/doc/examples/mpg123_to_out123.c?view=markup
> 
> and let out123 do the ALSA dance, but it's your pick;-)
> 
> 
> Alrighty then,
> 
> Thomas
> 
> 
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Leonard Bocock
leo...@gm...