Summary:ASTERISK-29455: Local channels (dialed using Originate dialplan application) play back gsm files over ulaw files when both exist
Reporter:N A (InterLinked)Labels:patch
Date Opened:2021-05-27 12:38:21Date Closed:2022-11-08 09:16:01.000-0600
Versions:18.4.0 Frequency of
Environment:Attachments:( 0) translate.diff
Description:Strange issue with codec conversion that I noticed today. Despite the translation costs of slin192 <-> ulaw and slin192 <-> gsm being identical, an slin192 will pick a gsm audio file if both a gsm and ulaw candidate exist for a specific file. It plays ulaw files correctly if there isn't a candidate (same name) gsm file.

The correct behavior should be that ulaw is preferred over gsm, since the costs are identical, and ulaw is the higher quality codec, and being both uncompressed and raw audio, closer to slin format than gsm would be. Yet, it falls back to the lower quality codec for some reason which seems arbitrary.

An analysis of the ast_translator_build_path() function in channel.c along with DEBUG messages confirms the problem occurs here, and likely the actual bug lies with the ast_translator_best_choice function in translate.c.

It appears this function looks only at translation costs and the choice between two codecs can be arbitrary if costs are identical.
Comments:By: Asterisk Team (asteriskteam) 2021-05-27 12:38:25.546-0500

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By: N A (InterLinked) 2021-05-27 13:30:50.899-0500

The attached diff successfully resolves my *specific* issue. Some algorithm for determining if one algorithm is (from a quality perspective) superior to the other would need to be called here.

By: Friendly Automation (friendly-automation) 2022-11-08 09:16:01.985-0600

Change 15953 merged by Friendly Automation:
translate.c: Prefer better codecs upon translate ties.