Low quality videos

Question

Not sure this is the right forum. I'm creating a video in iMovie which looks fine when exported to M4V format but quality degrades in spots when encoded to FLV format with Media Encoder CS4 so I can import it into a webpage with Dreamweaver.
Below are screenshots from before and after encoding with Media Encoder.
I've chosen the default options, but Sorenson doesn't make any difference. Not sure what options will help.
Not all of the video is so badly degraded. A couple of still shots look fine as do various other video clips.
I'm no expert but I've encoded a few jobs before and haven't seen anything like this before.
Thanks for any help.

Answer 1

When transcoding video (converting from one format to another) you can never improve the quality, only degrade it. So when you take a highly (very effectively) compressed video file like the m4v and then recompress to a less effective file format like the .flv, there is a great likelyhood that quality will degrade.
The best way to avoid that degradation is to ensure that you have more than enough video data to start with so that even if some of that data is destroyed in the conversion process, you have more than enough to meet your quality expectations.
Video quality is generally tied to the "video bitrate" of a video file... espressed in kilobits/sec. And that video bitrate is most effective at only one display resolution. So a very low video bitrate of say 200kbps could have the exact same quality when displayed on a very small display as a 2000kbps video file being displayed on a much larger display.
And while you may have chosen Sorenson as your compression, the bitrate and display dimensions settings are actually much more important. As a rule of thumb, if I have to transcode, I always start with a file bitrate that is double what my final out file will be... so that even if half the data is destroyed during convertion, I still get the quality I want.
So to end up with a 1000kbps bitrate video file, my original file has to be a 2000kbps bitrate file.... and remember that the bitrate is really only effective for one display size... not something larger.
I'll include a short article on bitrate at the end of this post.
But actually... I'd like to advice AGAINST converting your video file to an .flv file (and I'm a Flash developer!!).
The m4v is a very effective compression format and will work super great for the Internet because it will be viewable on iProducts as well as PCs... which the .flv file will not.
I'm moving almost all my new videos from .flv to .m4v and using the JWPlayer to display on the Web page... here's an example:
http://exploreolympics.com/reports/?p=5007
Plays just fine on iPhone or PC!
Don't confuse DW with simple WYSIWYG HTML editors, you can insert any video code yu want with DW... not just that for .flvs
Check out JWPlayer... it will generate your code for you:
http://www.longtailvideo.com/players
Bitrate review:
Video bit rate
Video bitrate is the minimum amount of data that must continually flow into the video player in order for the player to display that particular video uninterrupted. If that supply of data is not high enough, the video player will stop…. Wait for more data to download, then resume. The video bitrate is set as a parameter when the video is encoded.
One of the principle of goal setting is to "Begin with the end in mind". In this case it'll be very hard to give good recommendations because the end is not defined. So I'll just make a few assumptions and you can correct me as needed.
First, I'll assume that since you are converting to Flash, you want to deliver this video over the Internet. If that's true, then we'll have to make some assumptions on the Internet connection download speeds of your potential viewers. Let's just say that most have at least a 1.5Mb connection or faster.
OK, that would mean that a video bitrate of half that should usually provide a video download that is not interupped by buffering (most of the time anyway). So assuming a video bitrate of 750kbps, what would the optimum display dimensions be?
Before we decide, here's a little info about bitrate. For highest quality playback, the video bitrate is tied directly to the display dimensions. That is, the larger the display, the more incoming data is required to properly display the video. Think of bitrate in terms of a can of paint. If you have 1 quart of paint, you might be able to do a very nice job on a 32 X 24 foot area. But if you try to stretch that same amount of paint out over a 64 X 48 foot area, the coverage will not be nearly as good and you get poor results.
In the same way, a video displayed at 640 X 480 pixels will require 4 times the bitrate as a video displayed at 320 X 240 pixels to produce the same quality. So for example a video with a bitrate of 100kbps, displayed at 160 X 120 will produce the same quality results as a video with a bitrate of 1600kbps if displayed at 640 X 480.
So to boil it all down, video bitrates of 750kbps, even up to 1000kbps can usually get delivered of the Internet on most high speed connections. Higher bit rates may work for really fast connections but will cause problems for viewers with slower connections. Video display size has a direct bearing on the final quality. In the 750 to 1000kbps range, display size should be kept around 450 or 500 width max (and whatever height the aspect ratio calls for). Yes it can be displayed larger, but the quality will suffer.
Sound like your audio settings are fine, especially for Internet delivery.
As for framerate, maintain the original raw video framerate for best results. So if the video was shot at 24fps, leave it.
As for video converters, do you have the Flash 8 Video Converter? It works just fine for video to be delivered over the Internet. Remember, you are taking a Cadillac version of video (h.264 HD) and stuffing it into a Chevy body to get it to work over the Internet.
Best wishes,
Adninjastrator