• Blogs
• Forums
• Tradeshows
• Partners
• White Papers
• Podcast Show Notes
• Events

 

Distribute Expertise: Encoder Shootout

Jan 1, 2009 12:00 PM, By Jan Ozer

An on-the-job comparison of sub-$1,000 streaming-media encoders for the PC.

If you produce your streaming-media files on a PC, you have multiple sub-$1,000 encoding options — including Adobe Media Encoder (AME), Microsoft's Expression Encoder 2 (VC-1 only), On2 Technologies Flix Pro (Flash only), Thomson Grass Valley ProCoder 3, and Sorenson Media Squeeze 5.0.3. In this overview, I'll compare each product's codec-specific features, encoding speed, and output quality to declare a winner or winners for each of the major three formats: H.264, VP6, and Windows Media Video (WMV) 9/VC-1. (Editor's note: Telestream announced and shipped the Episode Desktop Media Encoder for Windows after our editorial deadline. We hope to review that product and report our results sometime in early 2009.)

Last issue, we covered sub-$1000 encoders for the Mac. To set the stage for the Windows comparison, I've repeated my testing methodology here; you may recognize it from last month.

If you encode streaming video at sufficiently high data rates, all encoding tools look great. For many producers, however, this is useless information; if you're a high-volume producer, bandwidth is money, and you need to know which tool offers the best blend of quality and low bit rate. So I pushed the data rate on my tests below comfortable limits to see which tool retained the highest quality.

Specifically, I produced my SD tests at 640×480×30fps at a video data rate of 468kbps and audio data rate of 32kbps, using two-pass constant-bit-rate encoding (CBR) for VC-1 and two-pass or multipass variable-bit-rate encoding (VBR) for H.264 and VP6. With all tests, before comparing the results, I checked to ensure that total file size was within 5 percent of the target, which often required multiple re-encodes.

In high-definition comparisons, I used a 720p file (1280×720×29.97fps) encoded at 800kbps in two-pass VBR, with 128kbps audio. As with the SD test file, I encoded using a pre-scaled and pre-de-interlaced test file rather than encoding the original HDV source (or DV for the SD trials) and allowing the encoding tool to scale and de-interlace. That way, I could isolate pure encoding quality, rather than an amalgam of the encoder's scaling, de-interlacing, and encoding skills. More on de-interlacing in a moment.

The final test involved a 1024×768×15fps screencam capture encoded to 200kbps video and 32kbps audio. Screencams are a great training option for many software vendors and IT support folks, and there's a significant variation in encoding quality among the many encoders.

As you'll see below, with each set of tests — SD, HD, and tutorial — I grabbed and compared frames produced by each encoder. I also played each video in realtime to evaluate motion quality — in particular looking for banding and color shifting in video backgrounds and artifacts such as mosquitoes, or faint lines hovering over sharp edges. I rated each encoder on both still and motion quality.

OK, back to de-interlacing. Since many producers still shoot in interlaced formats or need to convert older, interlaced source material, the ability to de-interlace the two fields in their videos into a sharp, cohesive frame is critical to overall encoding quality. To test each encoder's de-interlacing skills, I used a DV file containing a minefield of sharp diagonal edges, slanted guitar strings, spaghetti-thin Venetian blinds, and other de-interlacing challenges. With each encoder, I input the test file, output a scaled, de-interlaced 640×480 file, and compared the results. You can see a frame from this test file in Figure 1.

Continue the discussion on “Crosstalk” the Millimeter Forum.
© 2009 Penton Media, Inc.