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Facts and Fiction of GPU-Based H.264 Encoding
notthatwillsmith writes "We've all heard a lot of big promises about how general-purpose GPU computing can greatly accelerate common tasks that are slow on the CPU — like H.264 video encoding. Maximum PC compared the GPU-accelerated Badaboom app to Handbrake, a popular CPU-based encoder. After testing a variety of workloads ranging from archival-quality DVD rips to transcodes suitable for play on the iPhone, Maximum PC found that while Badaboom is significantly faster than X264-powered Handbrake in a few tests that require video resizing, it simply can't compare to the X264-powered Handbrake for archival-quality DVD backups."
To begin with, x264 blows the water out of Badaboom in terms of speed when similar settings are used. Badaboom appears to use the rough equivalent of --aq-mode 0 --subme 1 --scenecut -1 --no-cabac --partitions i4x4 --no-dct-decimate in terms of x264 commandline... its no wonder its "fast" when they compare it to x264 on far slower settings!
GPU encoders won't be able to compete with CPU encoders until they either get a lot faster (in which case they'll compete in the "high performance" market) or they get much better quality, since at sane settings x264 unsurprisingly blows Badaboom out of the water quality-wise, too. Until then, the product is not only completely proprietary but furthermore simply inferior, and they're going to have a very hard time marketing it.
And it seems that I made a slight oversight here also; --qp 0 in x264 (in the standard as qpprime_y_zero_transform_bypass_flag) is set, H.264 can indeed be a lossless format too, making it the only MPEG video format with a lossless mode.
I don't know what your source is, but MPEG-2 can't even APPROACH MPEG-4 AVC quality at the same bitrate (at low bitrate), and MPEG-4 AVC can produce a much more compact file for a specified quality (such as where DVD-quality or better). On the other hand, MPEG-4 is much more recent, and takes an order of magnitude more processing power to encode and decode. MPEG-4 uses much improved intraframe compression, variable-size macroblocks, and more advanced descriptions of block motion. Even if we drop the issue of MPEG-2 support for B-frames and limits on P/B frames per GOP (limited by the MPEG-2 profiles, which could be ignored), MPEG-4 is much more efficient at removing redundant information. Finally, MPEG-4 adds more advanced entropy coding for the final lossless compression of coefficients, etc after lossy compression is performed -- the CAVLC coding is an improvement on MPEG-2's standard variable-length coding. CABAC's arithmetic coding is even more efficient than CAVLC.
MPEG-4/AVC was intended to deliver comparable quality to MPEG-2 at half of the bitrate, and certainly succeeds at low bitrates. At higher bitrates (near-perfect picture quality), you certainly would have been right about the Advanced Simple Profile for MPEG-4 (used in Divx, Xvid, etc), but AVC should still be more efficient.
Incidentally, the MPEG-2 profile allowed in DVDs was picked to ease the work of the decoding hardware (savings on cost for consumers), at the cost of compactness. The fixed resolutions, bit rate limitations (both max and min bitrates), and GOP limits make it much easier to create a compatible hardware decoder. Yes, they can sometimes significantly decrease compression, but they made early DVD players marketable. Within these significant limitations, the studio-grade encoding software and technicians are PHENOMENAL at delivering maximum quality. If you're used to consumer grade MPEG-2 encoding, something like the pro version of Cinema Craft Encoder is a revelation (an expensive one though -- nearly $2K). See if you can sniff up a trial or demo, and compare the output quality to premiere.