Bitrate Calc Question

[cquetsch]

Had 4 episodes of a TV show in AVI format I wanted to dump onto DVD. I added up the time of all 4 episodes and entered this into the calculator along with 2 channel audio. When the AVI to MPEG conversion was completed the collective file size was much more than a single DVD could handle. The 4 WAV files that were created by Canopus were obviously not factored into the equasion by the calculator.

I then re-did the calculations but this time entered 8 audio channels (4 episodes x 2 channels). The resulting collective file size was as expected.

Is it proper procedure to take multiple AVI's, sum up their running time and expect the calculator to give accurate results? Why did I have to enter 8 audio tracks as a work around? Why would 4 seperate smaller conversions be any different in terms of calculation from 1 large conversion. 3 hours of video is 3 hours of video no matter how many pieces you cut it into.

Everything worked out in the end but I want to understand why.

Thanks

Chris

[manono]

Hi-

Is it proper procedure to take multiple AVI's, sum up their running time and expect the calculator to give accurate results?

Yes, if you do it right, like fill in the bitrate of the audio correctly.

Why did I have to enter 8 audio tracks as a work around?

Just coincidence. The number of channels shouldn't matter. Only the bitrate matters.

Why would 4 seperate smaller conversions be any different in terms of calculation from 1 large conversion.

It's not.

Everything worked out in the end but I want to understand why.

You didn't take into account the WAV audio you got. As a side note, no one uses WAV audio in such a DVD. Had you converted it to AC3 or MP2 audio, maybe your first result would have worked.

[cquetsch]

Thanks Manono for your quick response.

Your absolutely right!!

I had Canopus set to output WAV audio instead of MP2. This is why the file sizes were unpredictable.

Chris

[jman98]

You didn't take into account the WAV audio you got. As a side note, no one uses WAV audio in such a DVD. Had you converted it to AC3 or MP2 audio, maybe your first result would have worked.

I'm not trying to be one of those guys who picks apart people's posts when they engage in hyperbole for the sake of making a point, but this is just dead wrong and you know it. Concert DVDs often use PCM audio (this is the same thing as WAV audio) as a sound option. I have plenty that do this. You probably do too. I've even made some DVDs from laserdiscs that were less than a hour long and I just used PCM audio because I had plenty of space to do so.

I suppose it's worth pointing out that while many authoring apps will let you use MP2 audio and most/all DVD players should play it, technically it's not allowed on NTSC DVDs, only on PAL DVDs and even then according to the specs there is also supposed to be also either a PCM audio track or an AC3 audio track.

Cquetsch - WAV output uses a bitrate of something like 1411 Kbps (it's something barely over 1400, but don't quote me on the 11 part - that might be a little off) compared to AC3 which will usually use 352 Kbps or less, so the use of WAV audio, though always valid for PAL and NTSC DVDs, did use up more space than you calculated for. You should also be aware that if you do VBR (Variable Bit Rate) encoding that depending on the values you set for your maximum and minimum bit rates that you can also overshoot an encoding target and end up with encoded files that are larger than you wanted because it's impossible to predict in advance the exact size a VBR encode will give. If your bit rate encoder says to use, say, 4511 Kbps, you are foolish to use this exact value. Always use a little less than the encoder says. At 4511 Kbps, everything will have to be perfect in your encode and all it takes are a few segments that overshoot the target bit rate (this happens with some encoders) and you'll end up with a file too large on a CBR (Constant Bit Rate) encode as well. Whatever value the bitrate calculator tells you to use, always use a value a little lower so you have a little breathing room in case your encode ends up bigger than you think.

[45tripp]

WAV output uses a bitrate of something like 1411 Kbps (it's something barely over 1400, but don't quote me on the 11 part - that might be a little off)

It's 1536 kbps for dvd video. 48khz sample rate. (2 channel)
1411 is 44.1khz.

[manono]

I'm not trying to be one of those guys who picks apart people's posts when they engage in hyperbole for the sake of making a point, but this is just dead wrong and you know it

Seen a lot of PCM WAV audio used in retail TV series DVDs, have you? Maybe you can point out a couple to me. Seen a lot of PCM WAV audio in 3 hours worth of videos converted to DVD from downloaded AVIs and placed on a DVD5?

It wasn't hyperbole and it's not wrong. We're not discussing retail concert DVDs. If I somehow gave that impression, I apologize.

[cquetsch]

Thanks jman98 for your insight as well. I think I have this whole WAV vs MPEG2 thing figured out now.

In manono's defense, he did mention that no one uses WAV audio in 'This type of DVD'. I think he was pointing out that when authoring a TV show to DVD, there is no need to preserve the fidelity by using PCM and thus reduce the available space for the video content.

I could see the point of using PCM for a concert DVD as in most cases the sound may be more important than the video.

I think the point got lost in semantecs. But I always appreciate a good debate, especially on my behalf.

Thanks again.