Replacing an audio track without re-encoding the video

[sbekin01]

I'm new to Audition CC so apologies for the basic question. I originally asked this in the Premiere Pro forum but I think it's more an Audition question..  I have AVCHD home video (MTS video with AC3 stereo audio) and have found I can clean up the audio, for example in speeches, very well in Audition. Is there a way to just replace the MTS's orginal audio track without re-encoding the video (which it seems I have to, if I do this via Premiere Pro)? In some cases the videos are poorly lit and any re-encoding makes them look noticeably worse than the original. In any event the video does not need re-encoding, I just need to replace the audio. Maybe I need to export the cleaned-up audio from Audition and use some other program to replace the audio in the original MTS file? Is that called re-muxing?  Thanks in advance for any help.

[emmrecs]

I don't have PP so can't be sure of this, but in the video editor I use the "audio" is always displayed as a separate "track" on the video editor screen.  If I want to replace the camera audio I simply place the replacement audio, exported from Audition, on the next available track, ensuring it is correctly lined-up with the existing audio track (to ensure lip-sync etc.) and then either mute or delete the original audio.  (Not sure about PP, but in my video editor I have first to "ungroup" the original audio from its video track to be able to delete it; once I am happy with the alignment of the "new" audio I will "group" this track with the video to ensure they stay locked together.)

[Olly_]

I have done that, by opening the MTS home video in Premiere Pro CC, selecting the clip in the Timeline, selecting 'Edit', 'Edit in Audition', 'Clip', which opens the audio track in Audition CC, where I clean it up and save, which returns me to Premiere Pro and I can play the combined result... the original video and the cleaned up audio track, which has replaced the original audio track. However it's the next step that foils me... To get a new MTS file with the new audio I have to save the changes, which re-encodes the video, which gives me a larger finished file with noticeably worse quality! So I'm starting to see that Premiere Pro can't do this. It has to re-encode the video as well as combining the new audio and I can't see any way to do that without video quality loss.

  On a positive note I think there's a way that I'm still checking. I can drag the MTS straight into Audition, fix the audio, save the audio track as a new AC3 file (in my case checking it's 48khz, stereo, 16bit, 256kbps and Dolby Digital, not Dolby Digital Plus) and then use an open source program Avidemux to open the original MTS video, leave the main screen settings as Video Output..Copy, Audio Output..Copy, Output Format..MKV Muxer (not sure about this option, there may a better choice) and in the Audio menu..Select Track, in the Track 1 dropdown..Add Audio Track, then OK, play to check it's OK, and Save as a new MKV video file. The change in container from MTS to MKV seems OK and there's no video re-encoding. It's very quick, there's no video quality loss, the new audio is seamless and in-synch, the final file size is very similar to the original, and 'Media Info' shows the key internal video and audio specs are the same as in the original MTS video. I'll test some more and see if there are issues I haven't seen yet (I've only done one video so far).

[Bob_Howes]

This is actually more of a Premiere Pro question than you know.

MTS is just a wrapper extension for a variety of video types...and the AVCHD you mention is (as I understand it) based on MPEG 4 coding.  One of the things with MPEG coding is that audio doesn't exist as a discrete file as separate from video--both audio and video are coded together.

However, after you've edited in Premiere Pro (even if it's just opening the video to process the audio) on export you have a wide selection of export formats.  Depending on what you want to do with the videos once you're done, you should be able to find an export format that does little or no damage to your original quality.  However, you'll need to think about what format/codec is most suitable for what you want to do with your finished product.

...and, on that I suggest you may wish to visit the PP forums!

Edited to add...I forgot to mention that a little utility called Media info is very useful to analyse exactly what format your original files are:  MediaInfo

[ryclark]

Don't know about Premiere but any decent video editing should be able to re-multiplex the video and audio together into one video file without having to re-render anything. But you must, of course, choose to save it in exactly the same format as the original. Also the edited audio from Audition may have to be re-rendered in order for it to match the original audio from the MTS file as Audition always works with .wav files internally.

[Olly_]

Thanks Bob and Ryclark.

  Bob, our aim is to copy these videos onto USB sticks, for our family to watch on our various home TVs, from a media player such as WD Home TV, a media PC or a laptop via HDMI cable. I expect the original MTS files, with cleaned up audio, will be fine. Media Info shows these to be video: AVC format, variable bit rate, 16.0 max bit rate, 1920x1080 pixels, 25.000 fps, 8 bit, interlaced; audio: AC3 format, 256 Kbps bit rate, 2 channels, 48.0 KHz sampling rate, 16 bits bit depth. I'm keen to avoid re-encoding the video, and it seems I can. My initial test worked and tonight (I'm in Australia) I'll test further... I can edit the AC3 audio in Audition, export it as a new AC3 with the same format as original, then use some other non-Adobe program to replace the original audio track with the new one, without touching the video.

  Ryclark, I believe you are right. My novice-level understanding is that the process of separating the components of a video file such as my MTS file (video, audio and possibly others) into separate files is 'de-muxing' and putting them back together is re-muxing. Audition can save or export the original or edited audio track of my MTS file to a separate file so I assume that's like a specific audio de-mux. However I don't think Adobe products can re-mux without re-encoding the video (slow, larger resulting file size, worse video quality!), so I need some other program to replace my MTS file's audio with the new/edited audio.

  So far I've found the free-ware Avidemux can do it but past experience is that free-ware can be a bit flaky or over time not as bullet-proof as a good/proven commercial product, so I'll look a bit further - or does someone in this forum know of such a product? HD Video Converter seems to be an option but it looks a bit amateurish.

  By the way, if anyone is after a cut/join program to remove unwanted parts of a video without re-encoding the whole thing (ie. fast, same file size and unchanged video quality) I found Avidemux (free) only works on whole frames (GOP?) and the joins can have a little 'flick', whereas for $40-$50 a program like Fame Ring Smart Cutter for MTS videos (the Sony vidcam home video files I'm interested in) is frame accurate (it only re-encodes around the cut points) and works very well (smooth cut/join points). Smart Cutter doesn't do AVI videos (for my PC screen-recording videos) but I found SolveigMM Video Splitter Home Edition works well with those (not so well with my MTS files).

[emmrecs]

Olly  wrote:

By the way, if anyone is after a cut/join program to remove unwanted parts of a video without re-encoding the whole thing (ie. fast, same file size and unchanged video quality) I found Avidemux (free) only works on whole frames (GOP?) and the joins can have a little 'flick', whereas for $40-$50 a program like Fame Ring Smart Cutter for MTS videos (the Sony vidcam home video files I'm interested in) is frame accurate (it only re-encodes around the cut points) and works very well (smooth cut/join points). Smart Cutter doesn't do AVI videos (for my PC screen-recording videos) but I found SolveigMM Video Splitter Home Edition works well with those (not so well with my MTS files).

Glad to hear you've solved the problem you had and now have the video files as you want them!

However, I do have a suggestion of a totally free and reliable (no downside at all that I have seen) program for joining those MTS files into one continuous playback.  I, too, use MTS files with cameras that record to internal HDD and hence have a maximum capacity per file of 2Gb (about 16 minutes of continuous recording).  Where the "new" file starts there is always a degree of discontinuity, your "flick".  TSMuxer will successfully join all these separate files into one continuous file; the most I have ever needed to join was a set of 6 (video of a wedding service), complete c.10.5Gb file plays without "interruption".

[ryclark]

I'd be surprised if Premiere Pro can't re-mux without re-encoding the video. But you will have to ask on the Premiere forum about that one.

[sbekin01]

Thanks emmrecs and ryclark.

   emmrecs, Since my last post I also found tsMuxer and it's great. I use it to replace the original MTS video's AC3 audio track with one I've cleaned up in Audition, without re-encoding the video, so it's fast and no video quality change. I previously mentioned using Avidemux for this but later found it seems to drop the odd frame at the start when replacing an audio track, whereas tsMuxer does it perfectly. I'd also use it as you say to join MTS videos but mostly I need to cut and join, for which I'm finding Smart Cutter ($40) works very well; it 'smart renders' just a few frames around any cuts, with perfect joins, is fast, and with no overall video quality change.

   ryclark, I have been Googling and asking on the Adobe Premiere Pro forum but I do not believe it can re-mux a replacement audio track. It has to re-encode the video as well, which is slow and I end up with a bigger file and worse video quality, so that's out for me. It also can't smart-render the way Smart Cutter does. It has to re-encode the whole video, again not what I need. With the non-Premiere Pro workflow I now have, including using MkvMerge as a last step (also no video re-encode), I get the new audio and trimmed/joined MKV videos, fast and with no overall video change.

   On a general point, if I have to make a video smaller, to put on a social website, from what I've seen (not much really, I'm still new at this) I'll use Handbrake, not Premiere Pro. It's simpler and has great reviews for getting optimal quality/size. Compared to that, Premier Pro CC seems arcane, with having to somehow know the best settings for the Project, Sequence and whatever other Adobe program does the actual re-encoding. With no re-mux, smart-render or simple best-quality downsizing, all I'm currently using Premiere Pro for is to play/scrub videos to decide on cut/join points (it's hardware acceleration is great). Later maybe I'll experiment in Premiere Pro with micro-contrast, contrast, brightness and sharpen effects, which I know will mean I'll have to re-encode the video, so I think I'll only rarely do that; the videos straight out of my Sony vidcam are pretty good for my purposes.