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[Off-Topic] Random Observations

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CwF
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[Off-Topic] Random Observations

#1 Post by CwF »

Some days just don't work...Get comfortable, a cup of tea maybe. TL;DR

Some may have notice the tv.tk gui I use for broadcast tv on my computers. That's working well, no updates yet. There has been an issue with the hauppage quad tuners forever that causes an error in the audio stream. While caused by the varying quality of reception and the numerous possible error modes encountered, this error is hardware I think.

Since Stretch I've been using them and on that first machine the firmware was not officially available, so I hacked it in there... The error in question concerns the 2 pairs for 4 total architecture. If a pair is used to pass off recording of a binge, like 3 hours on 0 then do another 3 hours on tuner 1, then there is an overlap of a few minutes. Occasionally I might save something and span that overlap by appending the two together. At that splice, the audio drops for the duration of the second file. bummer...

For years I've taken a look now and then for lots to learn with questionable gain. The source of the error seems to be time stamps, and a mismatch between the files. Time stamp errors have many manifestations yet this drop out boggles me. MPV will stream the errors if I use a terminal and there are thousands scrolling by. Mediainfo sees the streams, audio is there, mpv plays it fine, but using avidemux.appImage just can't deal with it. It claims there is no audio! Well, avidemux is the problem here since it is a step I use and the one that mangles the result. I have not narrowed down the versions since there are 3+ versions in use over the years. Even though it seems the culprit, there's more.

On Buster, or maybe Bullseye, the firmware is official. Also 5 times the size of what I was using. The character of this issue has changed. The audio is now garbled, not silent, after passing from avidemux. MPV and mediainfo still see a usable input file but avidemux mucks it up. Just today I noticed this change.

So, the computer recorded a binge, caught a pilot of an interesting show I decided I'd like to watch before it gets recycled, that's overwritten. And sure enough, since I want to process it, the audio was screwed opened in avidemux. So the mood struck, let's figure this out. I've been using ffmpeg directly more often now and thought to cli some magic to avoid avidemux. ffmpeg simply dropped the ausio track using "-codec copy". Strange, it kept the subtitles? So it effects more than just the appimage. I substituted "-acodec copy" to force copy that missing/garbled audio track...

Well, it worked. The output file had a clean audio track! But, it also compressed the video which I didn't want/need. I usually prefer to send things through handbrake, add tags, and use h.265 if I want to keep them for awhile. During this unintended compression I noticed ffmpg on cli does not have the 'nice' settings of handbrake. It used 20 cores at full turbo, interesting. Handbrake doesn't do that, typically using 7-12 cores and sitting at non-turbo duty clock - so I don't really notice it running. No hurry.

So, I open the fixed audio version in avidemux and export the audio track. Then open the original as recorded video silent audio and imported the audio and started to edit the commercials out only to find it was not editing the audio...So save the whole thing to a temp mkv, open that, edits working on all streams! So a long workaround...

About 60% into the file I see a banner scroll, the audio gets muted, "blahmp blahmp blahmp broadcasting from a WW2 RCA deep in a bunker we bring you this emergency weather alert blahmp blahmp blahmp"

Seriously?...

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