I'm not particularly well-schooled on the intricacies of this stuff so I've come here seeking help; I'll try to keep things succinct. I use a Hauppauge HD PVR Rocket to capture material from my Satellite box, it records in mp4 format to an NTFS-formatted USB drive which I then transfer to this computer. However, I'm having some curious inconsistencies both with audio and video playback that I'm at a loss to figure out.
The audio issue is that it's very good in certain players (PotPlayer, SMPlayer) but extremely weak/near inaudible in VLC, Windows Media Player and Media Player Classic). I presume I'm missing something simple here but it's a little frustrating.
The video issue is more perplexing. In two of my recent recordings a section - not all, probably about 25/30% of the playback is too fast, perhaps 1.5x speed rather than normal speed. Either side of the fast section things are fine, and this problem again only happens in select players although it's even more inconsistent (one is too fast in PotPlayer, one isn't, both play too fast in VLC).
This has so far only happened when I've been recording HD content; anything I've recorded from SD feeds doesn't seem to have the playback speed problem (it does have the audio one, but didn't until I started trying multiple players).
There's a third issue whereby in VLC every time I skip to a particular section I get a grey embossed-style interference over the top of my picture which lasts a second before disappearing; this doesn't happen in PotPlayer, SMPlayer or Windows Media Player.
I've checked my graphics drivers (NVIDIA GeForce 9600 GT, a bit old now but I scarcely have need for anything more than that at this time) for the latest stuff and apparently there's nothing to download, but I've really got little idea about my codecs etc.
Any help would be sincerely appreciated; I'm hoping it's relatively simple because there are circumstances in various players where things are fine but none yet (with regards the problematic files) where they're all within the same player!
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Some players let you increase the volume beyond 100%. I can really only speak for MPC-HC as it's what I use. The default maximum is 100%. To boost the volume further you need to go into it's options and under "Audio Switcher" adjust the "Boost" fader. Going beyond 100% can cause louder sources to distort though.
For the speed problem.... I'm guessing.... but I've seen something similar happen when the player gets the audio sample rate wrong and the upshot of it seems to be the playback speed ends up wrong. As an experiment.... try opening one of the problem MP4s with MKVMergeGUI (because it's easy) deselect the audio, save the video only as a new MKV and test it for playback speed. That might be somewhere to start.
"Embossed-style interference" might be the player not navigating to a keyframe, or correctly decoding any required info from other frames for the frame being displayed. You could resave (remux) the MP4 to see if it's a muxing problem. In fact if the video is being encoded and written to MP4 "on the fly" you might find remuxing fixes everything (except the audio volume). You should be able to remux them with My MP4Box GUI if you want to keep them as MP4s, or try MKVMergeGUI for MKV output.
Thanks for that. I've used MyMP4BoxGUI to demux and then remux one of the problematic files and it does solve the speed problem but not the audio issue; the audio remains accelerated in places and therefore in the remuxed video loses sync completely at the point where it begins to accelerate.
I'm going to try MKVMergeGUI now.
I've attempted to convert the audio to ac3 and then remux but that only leads to the same issue as in post #3; the video is fine but the audio remains accelerated and ultimately way out of sync. Still don't really understand why it's only happening a) selectively in terms of recordings and b) selectively within problematic recordings and would love to solve it asap.
I don't have the answer as to "why". I've just come across this problem on the odd occasion, although not for a very long time. I can't even recall if I found a way to fix it, but it does seem like a problem with the audio.
By default, MPC-HC is set to automatically load "external audio". If you have a video and audio file in the same folder and they have the same name, when you open the video file with MPC-HC it'll automatically include the audio. I recall a couple of times I didn't need to mux the audio and video into a single file to experience the speed problem. The video file by itself would play correctly. Add the audio stream to the same folder so MPC-HC loads it and the video plays at the wrong speed, yet I think the audio on it's own was okay..... that sort of thing.
Can you upload a small sample where the video is playing too fast or where the audio becomes accelerated? It kind of sounds like the audio sample rate is changing but the player doesn't know, if that's possible. Maybe someone else (or me) could look at it to see if they can find a solution. To be honest I can't remember, if when something similar has happened to me in the past, I always found a way to fix it.
Edit: One other thought.... does the audio always have the same number of channels? ie is it always stereo or always 5.1ch etc? If the number of channels changes at some point..... I'm not sure how likely that'd be to cause problems but it might be worth checking.
When I load it into MyMP4BoxGUI it tells me the audio is on 2 channels so it probably does change. My setup only uses HDMI cables (between sat box, splitter, recorder and television).
Here's a small sample, it might not play too fast in all players (does in PotPlayer, doesn't in VLC) but it's not without its issues in any of them tbh.
When I tried your sample (MPC-HC) I think the video was playing at the correct speed but the audio was coming and going.
I very much doubt it's fixable. It does seem to me like the audio is simply dropping out a lot, at least when it comes to the sample you uploaded. If you extract the audio from it so it's one continuios AAC stream, it kind of sounds sped up, but I think maybe that's just because there's so many small chunks of it missing.
Hmm, thanks again. I attempted a rerecording of one of the problematic videos and it came out fine so I guess it's just luck of the draw if and when this happens. Certainly a bit weird.