FixingCommonFileProblems

How to Fix Common Problems in Submitted Vids

Tools of the trade

How do I know there's a problem at all?

Well, there's two ways to know. One is to try it and see - running a file through a dvd authoring process and then watching it on a TV will usually reveal most of the problems listed here. The other way is to use MediaInfo on the file and to look at the results and compare to the specification that you expect that file to be.

For example, Vividcon expects m2v files to be:

and wav files are expected to be:

MediaInfo can tell you quite quickly if each of these things is true.

Audio Problems

The audio is mono

Use dbpoweramp to convert form mono to stereo wav.

The audio is not a wav

Use dbpoweramp to convert. You may need to install a codec for dbpoweramp to support conversion of this file type. If no codec can be found then try convertin with foobar2000.

AC3 files can be converted with BeSweet (or BeHappy).

Audio is the wrong sample rate

Fix with dbpoweramp.

Audio is not 16bit

Fix with dbpoweramp.

Audio is PCM and sounds like static

It's possible that the PCM is little-endian. It's a bit technical but when making PCM audio the byte order can be big-endian or little-endian and if played back the wrong way it just sounds wrong. The fix is to change the endianness. To do this you either need a program where you can specify the settings of the PCM file when importing (such as Audition) or I *think* BeSweet can support importing little-endian PCM do you could use that to covert. It's rare but annoying.

Video Problems

Video is not an elementary stream mpeg2 (e.g. has both video and audio in one file)

An elementary stream is one that has not yet been multiplexed (the process of combining, for instance, a video stream and an audio stream into one file or 'program stream'). DVD authoring tools require elementary streams as the multiplexing happens during the dvd authoring process.

If the video submitted is a program stream, we need to extract the video (and possibly the audio!) from it. This happens if folks send in a .mpg instead of a .m2v file.

To extract the .m2v, the submitted file must be demuxed. The tool I use is DGIndex which has a Demux option in the file menu.

Video is not even mpeg2!

If it's a video file at all, either ask the vidder to try again or just straight up convert it to a .m2v with LlamaEnc.

Video is not 720x480, is 720x576, 640x480 or some other generally 'correct' aspect ratio

Sometimes folks will send in, 720x576 (PAL-sized), 640x480 (square pixels 4:3) or some other aspect ratio that looks correct when played back but isn't actually 720x480. These have to be re-encoded so just run them through LlamaEnc.

Video is not 720x480 and is a weird aspect ratio

If the aspect ratio is 'odd' (doesn't look right when played in VLC or similar) and the file isn't 720x480 then the vidder will have to resubmit as we could only guess at what the correct aspect ratio should be.

Video has the wrong framerate

If it's 23.976fps then this is not a problem, it can be happily converted with a program called DGPulldown. It's also possible to use pulldown on 24fps and 25fps sources, but it's less standard so your mileage may vary and your authoring tool may or may not like the result.

If DGPulldown cannot be used or is not suitable for this video, the vid would just have to be converted with LlamaEnc.

Video is anamorphic but does not have the 16:9 flag set

This one is easy. These days, Llamamatic can fix this for us but before we used Llamamatic we'd use a tool called ReStream which will take a .m2v and allow you to change settings and save a new .m2v. Here you can change the aspect ratio to be 16:9.

Video has the wrong field order (motion is jerky on playback)

Just like aspect ratio, the field order of a .m2v file can be changed using ReStream. Just flip it to be the opposite of its current setting. If you've tried both Top Field First and Bottom Field First and both look wrong when playing the vid then the vid has a mixed field order. This cannot be fixed by anyone but the vidder :(

The video ends long before the audio ends

Is the download complete? If not then redownload or ask the vidder to reupload.

If it's the right file then this probably means that the video was 'converted' to NTSC incorrectly :( For example, lets say you have a 3 minute (180 second) vid that is 25fps and you tell an editing program to make a 29.97fps m2v file. Now lets say that the program just takes all the frames in the vid and assumes that they should be played back at 29.97fps which is much faster (more frames each second) than 25fps. 180 * 25/29.97 is 150 seconds, not 180. In this example, the video file would be 2 minute 30 seconds long but the audio would be 3 minutes (or just cut short at the 2 minute 30 mark).

Ideally the vidder should fix this either by sending you a fixed file or by sending you a file where they do not convert the frame rate so you can then do the steps you would normally do for an incorrect framerate file (see above).

You can, if you want, use ReStream to change the frame rate setting for the m2v but unless you are 100% sure what the correct frame rate is you could easily end up with a vid that is still out of sync and only the vidder would know for sure.

The audio ends long before the video ends

While it's *possible* that this is just like the bad framerate issue when the audio is longer, it's very unlikely. It's much more likely that either the video has not be fully transferred OR the wrong audio file (such as a non-edited version) has been sent.

Problems during dvd authoring

Buffer underflow!

This is the most heinous error during authoring. The technical explanation is that when multiplexing, the bitrate of the video went out of bounds for a fraction of a second and is non-standard. What this means to you is that you will have to re-encode the video, preferably with a different (lower) bitrate to try and get it to work. It's, unfortunately, a bit of a crapshoot and m2v encoding programs try very hard to avoid it but it does sometimes happen. There are a few tricks I can think of:

  1. Reduce the bitrate of the encode (sometimes doesn't help)
  2. Reduce the GOP to 10 or 12 (if you have access to these settings)
  3. Encode as an interlaced stream instead of progressive. It's less efficient but I've seen this fix the problem.

I can't mix 4:3 and 16:9 vids!

Yeah, it's a bitch isn't it? This is a limitation of the dvd standard that each Title must be consistent. A title on a dvd is something like VTS_01. The only way to mix 4:3 and 16:9 on a single dvd is to use one title per vid. However, this makes navigation really difficult because usually dvd players go back to the menu at the end of a title.

The way around this is very technical. You have to store the current vid in one of the dvd player's registers and then have a command that runs (for example a Pre command on a main menu) that determines what to go to next based on the number. So, if we're on vid 1 we jump to title 2 and so on until we are at the last vid when we jump to the menu. It's complex stuff. Llamamatic does it automatically and it's possible that other dvd authoring tools might have automated ways of doing this or might just yell "can't do it, too hard!" and tell you that you can't mix and match aspect ratios. It really depends on the authoring program.

Problems you notice after everything is authored

One vid is too loud/quiet

Llamamatic uses a program called Normalize on all the vids to try and get them to be similar audio levels. The default settings for the tool will convert to a sensible level so you can just use the command line:

normalize.exe C:\path\to\file.wav

The wav is overwritten by normalise so you may want to backup the originals before converting.

The vid starts abruptly as if the beginning was skipped

This is actually a problem with your dvd playing equipment and is, unfortunately, quite common. What happening is that the first chunk of the video is not being played. The only real way around this is to encode a second or two of black to the start of each vid. Or get a better dvd player.

The titles of a vid look cropped off

This is likely a problem with the TV or monitor you are using and is expected. Standard Definition video has a 'title safe' area which is a border around the frame of about 20%. Technically, titles should not be placed in this area as it's not guaranteed that a display will show them. These days titles can be happily placed in the 'action safe' area which is about 10% from the edge. Modern TVs have a mode to show the entire frame (Just Scan) which avoids this problem.

There's no fix for it other than to use a different TV (or have the vidder not do that in the first place)


Category/PC

Vividcon/FixingCommonFileProblems (last edited 2013-04-28 22:01:03 by AbsoluteDestiny)