Garbled sound on some HD recordings

[Post producer]

Confirm the shorter clip audio fault.ts does play correctly on VLC on my 14.4.1 machine also. But not on 16.4.1.  The results playing the files on Avidemux are the same on both systems in so far as the film title section music is unintelligible. One oddity is that the sound track of the Honda promotion on VLC cuts the final word "Honda" and then plays the title music correctly while Avidemux includes the word "Honda" but then fails to reproduce the title music. It appears that VLC is switching audio mode in some way at this point but Avidemux is not.

The TV headend program does not recode and the system records HD without problems most of the time. Random recordings in HD today from Channel4 and BBC1 all edited without problems.  Note that the two uploaded clips were from a Channel4HD transmission.

[Jan Gruuthuse]

It might be a change on the # of channels
i.e. 6 channels -> stereo -> 6 channels

Stream has mixed audio going from stereo to 5.1 as you just found out
Don't know how this will evolve in avidemux, developer wise.

[mean]

re-encoding  audio with mixer set to stereo *might* work

[Post producer]

I have now found that the file audio problem.mkv which has unintelligible sound in Avidemux and VLC, plays cleanly using smplayer on Ubuntu 16.4.1. So it is "just" a matter of correctly identifying the audio tracks and having the appropriate codecs. Any chance of this being added to the to do list? (The .ts file is silent on smplayer). Smplayer uses lavc:aac.

VLC results are not the same as Avidemux. VLC  audio is identifiable but overlayed with a loud 50 Hz buzz, Avidemux sounds as-though the speaker is underwater.

[fish]

Can I suggest a way that might get your job done. I use quite an old PCTV USB stick to make the recordings, so I'm not sure whether the problem is with that, as it gets a bit warm/hot after an hour or two of use. Most of the recordings have garbled audio after passing through Avidemux, even if no edits are made. These are files that play fine in Windows Media Player Classic after they are recorded but even when I just drop the file into Avidemux, video (copy), audio (copy), output (.ts) or (.mkv) or (.mp4) and then output without any edits, the audio in the resulting file is garbled.
I fix this (if fix is the appropriate word)  by first passing the recorded file through MKVToolNix and then into Avidemux for editing. When dropped into Avidemux the file from MKVToolNix crashes Avidemux but when Avidemux is restarted and the option to reload the crash file is chosen, I edit the file and get good audio. There is nothing elegant about this workflow but until I find the cause and/or a better way, it gets the job done.

Passing the file through MKVToolNix takes out some text files that are in the original .ts file. They may be teletext, as enabling subtitles doesn't show any subtitles in the original .ts file but a file of eg 1907Mb shrinks to 1674Mb after going through MKVToolNix.

Actually just now I have updated to MKVToolNix v9.4.0 ('knurl') and it's output no longer crashes Avidemux.

Edit. Spoke too soon, the next file crashed Avidemux but it still restarts ok.

[Jan Gruuthuse]

for old PCTV USB try with avidemux 2.5.6

[fish]

I have found v2.5.6 can neither display or edit DVB-T HD files, it can edit DVB-T (SD) files.  It's old but it's not that old.

[fish]

I stand corrected, I tried to edit a short DVB-T HD clip in v2.5.6 (32bit) just after posting. On loading the file there was the usual green screen and the next I frame button seemed to take the play head to I frames but with no video in the display. Then when the play head got to near the end the first frame appeared in the display. I then moved the play head to the start, hit play and got 'Trouble initializing audio device' , I hit ok and the video played. There are a few weird things happening, which may make it unusable for this type of file but that is further than I have got before with v2.5.6 and this sort of file. The problem seems to be audio related and messing around with settings seems to make things worse. v2.5.6 is a version I go back to if I have a faulty video file,  it seems to tolerate them better than v2.6.
For troublesome DVB-T HD  files that Avidemux refuses, I always fall back on an editor called 'H264 TS Cutter', it only handles H264 TS files and I'm not that familiar with the GUI but it has never failed to edit any troublesome DVB-T HD file I have thrown it's way. I think development has stopped quite a while ago at v111.

[Post producer]

Thanks for the comments.  I have installed MKVtoolsNix but after remuxing the problem file, the audio is still unintelligible playing on Avidemus, (app version 30). However, a second HD recording on a TS file that also has garbled audio on Avidemux is ok when remuxed to MKV. Four other recent HD recordings play correctly as recorded  To recap, the problem file is fine until the film starts at which point the audio fails.  The number of audio tracks switches at this point. The audio is normal during the ads. If I ignore the audio and edit the file, then save as MKV (but not TS) using copy/copy. VLC plays only the music without dialogue while smplayer is silent. All very confusing!

Note that the source recording MKV file plays correctly on smpayer (before editing) but not on VLC which sounds as though it is adding the sutitlles in with the audio

My systems are both Ubuntu so H264 TS Cutter is not an option.

[fish]

In cases like that I would treat the video and audio separately.  I would demux the video and audio using 'Yamb' (not sure if that runs in Ubuntu). Yamb will also allow you to choose which streams to keep or remove without re-encoding anything.

http://www.videohelp.com/software/YAMB

Actually looking at that it seems to be Windows only but either way treating the video/audio separately seems the way to go.

I hope something here will help get your task completed.

http://www.videohelp.com/software/sections/linux-video-tools

Actually just doing a bit of editing now and notice MKVtoolsNix will demux the video and audio for you. You might be able to remove any offending audio stream that way. Either way converting the audio, in a separate app, to uncompressed PCM might make more likely that the video and audio will sync without any shifting and you can recompress the audio (or not) while or after editing.

[Post producer]

It seems that one stereo track has music and effects, another has dialogue. There seems no consistency in the tracks used by any of the programs tested including Avidemux.
If i recode the audio in Avidemux, (rather than COPY), the replay of the result on both VLC and smplayer has the same "under water" effect. I cannot find any method of editing this recording with satisfactory audio although the source file plays perfectly on smplayer. I tried importing the source file into AUDACITY but although three audio tracks appeared, the dialogue track was missing and the third track seemed to be audio description. Unless Avidemux can be persuaded to cope with this audio track combination, time to give up I think!

[fish]

That audio description is for the partially sighted I think, I have come across that in some broadcasts. How many audio tracks do you see in MKVtoolsNix, did you try demuxing the audio and video?  If you don't like to be beaten and let's face it, you've probably spent more time on it now than it's worth, you could drop the original file into Handbrake, it doesn't refuse any valid file I've tried, just to see if that will give you a workable audio file, choose a low resolution for the video, it's the audio you're after. You could just edit what comes out of Handbrake's standard 'High Profile' or demux the audio from that output, if  it's good, then mux it with the video from the original. Think of it as practice to save something you really don't want to lose, or you could just give up, maybe a glitch in the broadcast or a broadcast flag or a glitch in you receiving the broacast, has messed things up and anyway you still have the original recording.

[Post producer]

Just to answer your question, MkvtoolsNix sees one stereo track and one mono track. Track one has dialogue and music, track two has the audio description. Using MkvtoolsNix, muxing with 1 and 2 or just 1 give the same result. Track two is not present. This results in a file with good audio on smplayer but burbling on Avidemux. Muxing with track 2 only, smplayer plays the audio description, (Avidemux is silent). As a further twist, the audio description has no connection what ever with the video.

I give up!

[Jan Gruuthuse]

I'm still convinced the problems start with recording (dvb-t/t2) is a multiplex (Crystal Palace muxes: several TV channels in one stream). Recording takes out the TV channel from that stream and probably there goes something wrong. Possibly something similar as happens here: ac3 audio unusable after a channel number switch
Having no access to that signal/hardware there is no testing possible from this side.
Possible causes:
DVBSky T9580 driver issue
TVheadend it seems you're behind with 4.0 :https://tvheadend.org/builds/tvheadend.

[Post producer]

Except that this is an issue with one HD recording only. On this contiguous recording, the previous programme and all links and ads during the recording play fine on Avidemux, but not the film sections.
Smplayer plays the entire recording without problems. On tvheadend, I am running 4.0.9 which is the current release source code. Development of 4.2 has been almost (99%) finished for quite a while.