|
Rockbox mail archiveSubject: Re: Corrupt RecordingsRe: Corrupt Recordings
From: Bluechip <csbluechip_at_gmail.com>
Date: Thu, 29 Dec 2005 00:40:07 +0000 > > Just noticed something that may be of interest. With reference > > to the dump attached below: > > > Notice how there is a difference of 3 between the Xing-Hdr > > frame count and the actual number of audio frames. > >The Xing frame count in rockbox recordings was never exact so >far, as it just uses the internal frame counter of the MAS. This >doesn't always match the number of transferred frames, there >seems to be some buffering going on in the MAS itself. The error >is usually 1..3 frames. > >With older rockbox, long recordings which overflow the MAS frame >counter as well as recordings made with prerecording active had >no Xing frame count at all. > >The MAS frame counter is a 20bit signed counter which doesn't >wrap but saturate (!!) at 0x7ffff. OMG! Surely you can't code that by accident!? The stupidity of signing the number I can accept as a typo or one of the enginners using a time machine and recording -2104 frames of audio. But: if (cnt<0x7FFFF) cnt++; ...LOL >Newer rockbox versions always write a Xing frame count, tracking >the MAS frame counter during prerecording and estimating the >count for long recordings using the recording time. When rockbox >resorts to estimation, the error increases, but it's still >better than nothing for estimating playtime and average bitrate. Oh well. I thought I may have spotted a solution, but it's all pretty academic anyway as the Xing/TOC is invalid, and correcting that, even on-the-fly, would be (possibly unacceptably) memory hungry. >All this will change when framewalking during recording gets >implemented (something that is on my list) as we won't use the >MAS frame counter any more. AIS, storing enough data to build a correct TOC might be an unacceptable overhead. So it could be a lot of effort for little payback. I think I'll attack the WAV codec on the Archos when I've finished my latest little project - lots of fun to be had once that is done :) >Regards, Jens Happy new thing, BC Received on 2005-12-29 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |