For the last few years, my family heads down to a friend’s beach house for some much needed vacation during the summer. The house is somewhat secluded and thus doesn’t have very good TV reception, so this year I was thinking about using my Zune 80 as a miniature Digital Video Player. That way, my kids can watch some pre-recorded movies, cartoons, TV shows, etc. on the “Big Screen” and I don’t need to bother with bring a DVD player, burning DVDs, etc. So, I began the process of investigating how I can do this with my Zune 80 device.
If you don’t already know this, you can use your Zune to output a TV-Composite signal from the headphone jack using a special cable (it’s the same cable used for the newer iPods devices). My Zune A/V Kit came with such a video cable, so I had all the necessary hardware to pipe video from my Zune to a standard TV set. Note, that using a TV-Composite signal doesn’t offer you the best video quality (comparable to the output from an older VCR). If I was really picky and wanted the best quality possible, I could invest in a new Zune dock and use video component out signals, however, my plan is to watch videos on an older TV set so doing so would be overkill in this application.
The next step is to create video files that would playback reasonably well on a standard TV set. Most of my current Zune videos are in 320×480 resolution format (30 fps). This works great for playback on my Zune at 700 kbps video rate, however, it looks pretty grainy when viewing on a TV display. So as a test, I converted a partial TV show (Source: MPEG2, 720×480, 30 fps, 8000 Kbps, 7 minutes duration) with several different video settings. Below is what I tried, and my comments regarding playback on a standard TV screen:
320×240, 30 fps, 700 Kbps (43 MB) – This is the standard video settings that I use on my Zune, and the TV display image is very grainy. In addition, there’s a lot of “video tearing”, where there is pixelation and blurring during any motion.
640×480, 30 fps, 700 Kbps (43 MB) – The 640×480 resolution looked acceptable, and the 700 Kbps was fine when the actors didn’t move around very much in the scene. With moderate to high motion in the scene, noticeable video tearing and pixelation occurred.
720×480, 30 fps, 700 Kbps (43 MB) – At 720×480 I actually noticed more video tearing and pixelation, when intuitively I would think the video quality would be better. Also, the file size is the same as the 320×240 and 640×480 resolution, which seems strange.
640×480, 30 fps, 1500 Kbps (85 MB) – The 640×480 resolution looked acceptable, and the video tearing wasn’t as noticeable compared to using 700 Kbps.
640×480, 30 fps, 3000 Kbps (163 MB) – These settings produced the best playback quality of all that I tested, however, there still was a slight amount of video tearing during the high speed motion in the scenes.
Note: All video files had an audio bit rate of 128 Kbps, and I used a Constant Bit Rate (CBR) for both the audio and video settings.
Now, I was standing about 3 feet away from the TV when I was doing these tests, so it might not be too big if a deal if I was sitting on a couch at 7-8 ft away. The 640×480 resolution seemed to work best, and the only matter to decide on was the level of acceptable video tearing based on the different video bit rates. So I would suggest using the 700 Kbps if you’re concerned with file size and don’t mind seeing occasional video tearing, or 1500 Kbps if you’re not too concerned on file size and want better video quality, and finally 3000 Kbps if you really want to minimize video tearing and don’t care about file size.
What’s odd about these tests, is that file size for the first three video files (all at 700 Kbps) were the same. I would have thought that the high resolution files would have a larger size, but that didn’t seem to be the case. It appears that the video bit rate governed the file size (maybe because the video setting I used was CBR (Constant Bit Rate) instead of VBR (Variable Bit Rate))?
As a test, I made a few more video files using a variable bit rate (VBR) for the video, while keeping the audio bit rate constant (since this is a requirement to avoid transcoding during Zune syncing). So basically, the video bit rate that I specify in the conversion will be an “average” rate, while the actual rate can vary up and down when needed. Here’s the specs on the 2nd set of test files I created:
320×240, 30 fps, 700 Kbps (average rate) VBR (43 MB) – This resulted in a video file about the same size as the CBR video rate, but the peak video bit rate is 1150 Kbps.
640×480, 30 fps, 700 Kbps (average rate) VBR (43 MB) – This resulted in a video file about the same size as the CBR video rate, but the peak video bit rate is 1122 Kbps. Again, the file size between the two different resolutions is the same for some reason.
640×480, 30 fps, 1500 Kbps (average rate) VBR (84MB) – This resulted in a video file about the same size as the CBR video rate, but the peak video bit rate is 2428 Kbps.
With all of these files using VBR, the video tearing was significantly reduced (in my opinion), with no sacrifice in file size. In fact, the 320×240 video file actually looked ok when I was sitting on my couch about 9 feet away. So in a pinch, playing 320×240 videos created with VBR for the video bit rate might be sufficient.
I’ve concluded that for all my future videos, I’m going to use the Variable Bit Rate (VBR) for the video processing, as it minimizes video tearing without increasing the size. In addition, I recommend using the settings of 640×480, 30 fps, 1500 Kbps VBR (video) for those video files which you plan to watch on a standard TV set.
So, it appears that I’ll be sufficiently armed to handle my kids with my Zune 80 on our next summer vacation!