[Asterisk-Users] Skips and Pops in Call Recordings - channel.c
Analysis
Adrian Carter
adrian at lei.net.au
Tue Dec 13 17:08:33 MST 2005
Matt,
I have a similar issue to the 'Skips and Pops' with the On Hold
music on my Ast 1.2.1 box. I've tried moving stuff to a RAM Disk, yet I
still get reports from agents that callers report that the 'music on
hold sounds horrible'.
It has squeaks and pops.. kind of like digital satelite distortion..
and looking at what you've said below, it kind of makes sense, since I
can gurantee to re-create the problem by just dragging out a sip phone
and dropping myself in a queue - All MoH sounds terrible, but the "Queue
Announcements" (Your caller X in the queue) come out perfectly everytime.
The one thing that doesn't sit with your explanation : I seem to
have ZapChannel users complain of the same problem. Im newish to
Asterisk, but I thought RTP only came into play on SIP/IAX/MGCP calls
... So the fact that I seem to have the problem when calling from a CO
Trunk line (well, Inbound PRI) into a digium 4 port PRI card means it
couldn't be RTP related? just frame related?
Adrian
Matt Roth wrote:
> List users,
>
> I've traced the writing of the leg files to two functions in channel.c:
>
> ast_write()
> ast_read()
>
> They both contain similar code, so I'm going to limit my analysis to
> one of them. If I'm misunderstanding anything or am flat out wrong,
> please don't hesitate to correct me. Your input is what I'm looking for.
>
> Below is a code fragment, with some extraneous stuff removed for
> brevity and some comments describing what I believe is happening.
> Please take a look at it, paying special attention to the comments
> I've added.
>
> My understanding is that if the channel is locked, the function will
> wait on the ast_mutex_lock() call until it is unlocked. Once it is
> unlocked, the function attempts to compensate for any loss of leg file
> synchronization by jumping the file pointer forward by some value
> based on the number of dropped frames. This puts a gap in the leg file
> which manifests itself as a popping sound in the format we are using
> (PCM), but which probably sounds a little different in other formats.
>
> My main concern is if this fragment is responsible for writing the
> frame to its destination via RTP. If it is, the skips and pops in the
> recordings would likely manifest themselves as dropped audio on the
> calls. Is this correct? Do problems in the recordings indicate
> parallel problems in call quality? The reports from our agents don't
> seem to support this, but looking at the code worries me.
>
> Thank you very much,
>
> Matthew Roth
> InterMedia Marketing Solutions
> Software Engineer and Systems Developer
>
> =====================================================================
>
> int ast_write(struct ast_channel *chan, struct ast_frame *fr)
> {
> /* Lock the channel */
> ast_mutex_lock(&chan->lock);
>
> /*
> ... Code Omitted ...
> */
>
> /* Check to see if the channel is blocking */
> CHECK_BLOCKING(chan);
>
> /* Switch based on frame type */
> switch(fr->frametype) {
>
> /*
> ... Code Omitted ...
> */
>
> /* Handle voice frames */
> default:
> /* Validate a function pointer */
> if (chan->pvt->write) {
> /* Validate another function pointer */
> if (chan->pvt->writetrans) {
> f = ast_translate(chan->pvt->writetrans, fr, 0);
> } else
> f = fr;
> /* Validate the frame pointer */
> if (f) {
> /* I'm not sure what this does, so please let me know if
> you do.
> I really hope that it's not responsible for writing
> the frame out to its destination via RTP. */
> res = chan->pvt->write(chan, f);
> /* If this channel is being monitored write the frame
> to the appropriate leg file */
> if( chan->monitor &&
> chan->monitor->write_stream &&
> f && ( f->frametype == AST_FRAME_VOICE ) ) {
> /*
> If some frames have been missed, jump the leg file
> pointer forward to keep the leg files synchronized.
>
> !!! I BELIEVE THIS IS THE SOURCE OF THE SKIPS AND
> POPS IN THE RECORDINGS !!!
>
>
> */
> #ifndef MONITOR_CONSTANT_DELAY
> int jump = chan->insmpl - chan->outsmpl - 2 *
> f->samples;
> if (jump >= 0) {
> if (ast_seekstream(chan->monitor->write_stream,
> jump + f->samples, SEEK_FORCECUR) == -1)
> ast_log(LOG_WARNING, "Failed to perform
> seek in monitoring write stream, synchronization between the files may
> be broken\n");
> chan->outsmpl += jump + 2 * f->samples;
> } else
> chan->outsmpl += f->samples;
> #else
> int jump = chan->insmpl - chan->outsmpl;
> if (jump - MONITOR_DELAY >= 0) {
> if (ast_seekstream(chan->monitor->write_stream,
> jump - f->samples, SEEK_FORCECUR) == -1)
> ast_log(LOG_WARNING, "Failed to perform
> seek in monitoring write stream, synchronization between the files may
> be broken\n");
> chan->outsmpl += jump;
> } else
> chan->outsmpl += f->samples;
> #endif
> /* Write the frame to the leg file */
> if (ast_writestream(chan->monitor->write_stream, f) < 0)
> ast_log(LOG_WARNING, "Failed to write data to
> channel monitor write stream\n");
> }
> } else
> res = 0;
> }
> }
>
> /*
> ... Code Omitted ...
> */
>
> /* Set the channel as not blocking */
> chan->blocking = 0;
>
> /*
> ... Code Omitted ...
> */
>
> /* Unlock the channel and return */
> ast_mutex_unlock(&chan->lock);
> return res;
> }
>
> =====================================================================
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--
Adrian Carter
Technical Manager
Leading Edge Internet
Web http://www.lei.net.au http://support.lei.net.au
Direct +61 2 6163 6162 Support 1 300 662 415
E-mail cartera at lei.net.au
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