NextPVR Forums

OK, I know you need to transcode video to MPEG2 (or MPEG1) as the MVP plays that natively, but what is the story with audio? In the past I have just transcoded the audio to mp2 as that is what I read others have done and it has worked well many times for me.

But if I have an Xvid that already has audio in MP3 format (and IIRC the MVP does both mp2 and mp3 natively), can I forgo the audio transcode completely (this is an option in GUI4ffmpeg) ?

• Will it be a (much) faster transcode if I say video only?
  
• Will it likely still be in sync if I choose NOT to trasncode the audio, as I understand the audio/video transcodes would split the two streams and remux them back together, so presumably keeps up with the audio sync in doing so?)

k.

[EDIT]Well, that was weird. When I turned off the option to transcode audio, it said I could only save the file as a Video Stream (m2v). Looks like I misunderstood what they meant about that option... :o
When I turned it on and tried to choose mp3, it always flicked back to ac3 (which I know it cannot do, at elast not without the mvpmc domgle). So mp2 was the only option anyway .... :o :o

jksmurf Wrote:[EDIT]Well, that was weird. When I turned off the option to transcode audio, it said I could only save the file as a Video Stream (m2v). Looks like I misunderstood what they meant about that option... :o
When I turned it on and tried to choose mp3, it always flicked back to ac3 (which I know it cannot do, at elast not without the mvpmc domgle). So mp2 was the only option anyway .... :o :o

I was curious, found this: http://forum.videohelp.com/viewtopic.php...io#1579479

Quote:While MPEG2 program streams with MPEG2 video+mp3 audio, and MPEG1 system streams with MPEG1 video+mp3 audio are both valid in the general MPEG sense, they aren't allowed for any of the popular consumer formats--VCD, SVCD, DVD. If all you want to do is watch on computer, fine.

But if you want to use in a consumer player, you'll need to convert to the appropriate format first (mp2 for (S)VCD, ac3/mp2/pcm for DVD).

So presumably the MVP falls into the category of the "consumer player" and thus mp2 is required (as ac3 is not supported except with another dongle). That explains why I can't choose mp3 for DVD.

Cheers HtV, for finding a simple and logical explanation.

k.

Well I think you could transcode it that way (well it should be possible ), but you have to find the parameters for ffmpeg yourself. I think GUI4FFMPEG doesn't want you to do it because it's a "weird" combination that won't work in most cases.

@ jksmurf, I wonder if you could make available for download one of the video's you are having troubles with. It sounds like you're having a devil of a time.

I'm with HTV. Maybe you have to try transcoding from the command line before you start using a GUI. Command lines can ive you the exact error that ffmpeg is experiencing...

I did a test just out of curiousity: I demuxed a mpg I had, then muxed the mpv with an mp3 (in Cuttermaran). The resulting mpg plays fine on my mvp.

From the FFMPEG-doc: http://ffmpeg.mplayerhq.hu/ffmpeg-doc.html#SEC10
`-acodec codec' Force audio codec to codec. Use the copy special value to specify that the raw codec data must be copied as is.
So that would mean: -acodec copy

This parameter would make ffmpeg copy the audiodata as it is. Am I right here? So that would come in place of the mp2 parameter.
Good luck. Or send over one of the files, or give a url. Would be fun.

Will produce a new file with the audio as a 44.1kHz stereo 128 kb/s mp3, with the video untouched.

Hi guys, thanks for all your responses!

HtV Wrote:I think you could transcode it that way (well it should be possible ), but you have to find the parameters for ffmpeg yourself. I think GUI4FFMPEG doesn't want you to do it because it's a "weird" combination that won't work in most cases.

@HtV, yes, that may well be the case! I think I'll ask the GUI man.

zehd Wrote:@ jksmurf, I wonder if you could make available for download one of the video's you are having troubles with. It sounds like you're having a devil of a time.

I'm with HTV. Maybe you have to try transcoding from the command line before you start using a GUI. Command lines can give you the exact error that ffmpeg is experiencing...

Zehd, I'm not having trouble really, and thanks for the offer to have a look at a snip of the file, unfortunately I have deleted the Xvid(AVI) that I downloaded. I think you're right though, my GUI4FFMPEG is limited in that respect, for whatever reason.

Now that I have a TOSLINK installed on my MVP (did a small write-up on that with a pdf here), I became quite excited about other formats such as MP3 and even AC3 audio out via the Optical out, so I was having a bit of a play with transcodes.

@4zm4r3d02 Thanks for the command line, the problem is I can't leave it at Xvid (AVI) as my PC isn't fast enough to transcode on the fly to the MVP; if I transcode it's always been DVD Video (MPEG2) with MP2 audio. I was just experimenting with MP3 audio rather than MP2 and my FFMEPG GUI doesn't seem to be able to do that, for some reason.

Cheers all,

k.

[EDIT] Over at the videohelp forum, where I asked about GUI4FFMPEG they said "MP3 is not in the DVD Spec, that's why it's trying to encode it to AC3. MP2 Is".

jksmurf Wrote:@4zm4r3d02 Thanks for the command line, the problem is I can't leave it at Xvid (AVI) as my PC isn't fast enough to transcode on the fly to the MVP; if I transcode it's always been DVD Video (MPEG2) with MP2 audio. I was just experimenting with MP3 audio rather than MP2 and my FFMEPG GUI doesn't seem to be able to do that, for some reason.

Cheers all,

k.

[EDIT] Over at the videohelp forum, where I asked about GUI4FFMPEG they said "MP3 is not in the DVD Spec, that's why it's trying to encode it to AC3. MP2 Is".

I find that converting Xvid to svcd mpegs produces files that my pc can serve easily, that the mvp will play. I usually do it with this command line:


This will produce an mpeg video with mp2 audio.

If the Xvid file has the audio encoded as an mp3, which they often are, you can use this line:


I've never used GUI4FFMPEG (that I can recall), but if it tells ffmpeg to transcode to dvd compliant files with the '-target ntsc-dvd' option, it will default to ac3 for the audio. If you want it to use mp2 or mp3, you must tell it so, with the '-acodec' option.

I use the ffmpeg.exe that is included with gb-pvr, version CVS, build 4759. I added the directory it is in to my windows PATH environment variable, so that I can run it from a command line in any folder.