Hard Labor – The best CPU for MPEG-4
Curtains up for MPEG-4! Right now there is hardly a more interesting topic for the majority of PC-users than the creation of video sequences in the space-saving MPEG-4 format or conversions to this format. The available amount of video material for MPEG-4 which, e.g. from the Internet, is constantly growing. Even the very latest movies that are still unavailable in European movie theaters can be downloaded as MPEG-4 videos from numerous Internet sites. The data volume is no longer a problem: in the past a single film required several CD-ROM’s in order to be saved as a video in MPEG-1 format, today however, up to 110 minutes of video material in high quality can be squeezed onto a single CD-ROM. In addition: writeable CD’s are very inexpensive and are practically ideal for MPEG-4.
In order to create MPEG-4 videos, or to convert existing digital film material, a lot of CPU performance is required, more than any other application demanded before. In our previous article concerning MPEG-4 (MPEG-4: Copying a DVD video onto a CD-ROM) we confirmed that for example, the conversion of sequences in MPEG-2 format to MPEG-4 required enormous computing power and a lot of time. As a consequence, we subjected the current processors from AMD and Intel to a detailled test. The key questions that we were concerned with were: which processor is best suited to the creation of MPEG-4 sequences and how high is the workload for the CPU during playback? The test included Intel’s Pentium III (Coppermine core) from 600 MHz to 1000 MHz, Intel’s Celeron with 667 MHz and 833 MHz, AMD’s Athlon from 1000 MHz to 1100 MHz and AMD’s Duron from 700 MHz to 880 MHz. Let one thing be said in advance: the processor is never fast enough!
MPEG-4-Conversion with the help of the Flask MPEG-Encoder: The conversion speed from MPEG-2 to MPEG-4 depends strongly on the processor used.
MPEG-4 Encoding: Which CPU is the best?
Video file in MPEG-4 format: Good sound and image quality can be attained with a data rate of 148 KB/s. Although the resolution is twice as high as that of MPEG-1, the data rate is lower than that specified in the MPEG-1 specification.
Let’s not forget: hardly any other application demands as much processor-power as MPEG-4 conversion. In comparison to most Office applications, which can be used with slower processors down to 400 MHz, a really fast processor is required for MPEG-4 conversion. In order to measure the performance of a processor during MPEG-4 encoding, we encoded a four minute MPEG-2 format video sequence using the progam Flask Mpeg. To do this job, the processor has to be able to handle two main tasks simultaneously:
- Conversion of the MPEG-2 video stream to MPEG-4
- Conversion of the AC3 audio stream to MPEG-1 Layer 3
Whereas the creation of the audio stream is principally the same as MP3 encoding, and doesn’t demand too much from the processor, the conversion of the MPEG-2 video part is extremely compute-intensive.
AMD Duron beats Intel Pentium III
This diagram makes it clear: the MPEG-4 encoding speed strongly depends on the clock rates of the processor and the front-side bus.
We used two test platforms for the creation of an MPEG-4 video: the first was a socket 370 system for Intel’s Pentium III and Celeron, the other test system was a socket 462 (socket A) system for AMD’s Athlon and Duron processors. Apart from the processors, both systems were equipped with identical hardware and software. The Flask Mpeg Encoder software was used to convert an MPEG-2 video into MPEG-4 format (also used in our last test). The test sequence was a four minute film trailer which contained an AC3 audio stream amongst other things.
The diagram above shows the time required by the individual processors to encode the video into MPEG-4 format. At first glance the following facts are obvious: the higher the clock rate of a CPU, the faster the MPEG-4 encoding stream. Whereas the Celeron 667 needed almost 20 minutes to encode the four minute film sequence (1,188 seconds), AMD’s Athlon 1100 MHz processor completed the same job in approximately 10 minutes (626 seconds). Also quite interesting: AMD’s value-for-money processor, Duron beat the much more expensive Intel Pentium III!
The fastest CPU for MPEG-4 video encoding is AMD’s Athlon 1100. The diagram shows an overclocked processor with a 110 MHz front-side bus.
The duel between the fastest currently available processors – Intel’s Pentium III/1000 and AMD’s Athlon 1000 – is virtually a dead heat: the Intel CPU actually required 20 seconds less than its AMD competitor to encode the film into MPEG-4 format, but it had a front-side bus clock rate of 133 MHz. AMD’s Athlon however, was only clocked at 100 MHz although it uses Double Data Rate technology. A multitude of marketing strategists on AMD’s side therefore prefer to refer to this front-side bus technology as a 200 MHz system.
The CPU with the best price/performance ratio when concerned with MPEG-4 video encoding: AMD’s Duron 650 can be overclocked to 825 MHz with a corresponding mainboard and then beats Intel’s Pentium III/800.
CPU for MPEG-4: Clock rate, FSB and L2 Cache
At this point we can definitely say that the creation of an MPEG-4 sequence demands incredible CPU performance. The encoding speed is principally dependant on the CPU clock rate. Furthermore, the front-side bus or memory clock rate plays an important role. The results of Intel’s Celeron with a FSB clocked at 66 MHz make this very clear as it yielded the worst conversion performance. The results of Intel’s Pentium III/1000 prove that a front-side bus overclocked to 150 MHz has notable effects on the MPEG performance. The processor attained much better results at 975/150MHz than the standard version.
Furthermore, our tests lead us to assume that the architecture of the AMD processors is better-suited to MPEG-4 encoding. The results of the overclocked Duron indicate this as it was only operating with a 100 MHz FSB but still outclassed the Pentium III with a 133 MHz FSB.
An ISSE version of the Flask Mpeg program would be interesting in order to investigate the streaming support propagated by Intel. The MPEG software currently only supports MMX instructions so that both AMD and Intel processors profit from this. The benchmark results also show quite clearly that the size of the L2 cache, which is integrated in the CPU core of all the processors, has a marked effect on the performance of the devices during MPEG encoding. Both AMD’s Duron and Intel’s Celeron have a smaller L2 cache and are therefore not in the leading group.
This is what an MPEG-4 video sequence looks like after it has been converted from the MPEG-2 format from a DVD-ROM. This video has a data rate of 150 KB per second at a resolution of 720 x 576 pixels with stereo sound (48 kHz).
CPU Load during MPEG-4 Playback
Having examined the processor-intensive task of creating MPEG-4 videos, we will now take a look at the ability of the individual CPU’s to play back MPEG-4 videos. In comparison to the somewhat overhauled MPEG-1 format which was most often used for video CD’s, the CPU load for MPEG-4 playback is especially high. Whereas MPEG-1 sequences could be played back on PC’s or notebooks with relatively slow processors, it’s a completely different deal with MPEG-2 and MPEG-4. In order to measure the CPU workload during MPEG-4 playback realistically, we analysed all the processors under Windows 2000 with the help of the Task Manager.
The processor with the lowest clock rate in the test was the Pentium II/450 and the fastest one was AMD’s Athlon 1100.
Average CPU workload of the individual processors during MPEG-4 video playback at full PAL resolution: whereas the Pentium II/450 was heavily loaded (80 percent) the load on AMD’s Athlon 1100 was only about 30 percent.
By Comparison: MPEG-4 three times the workload of MPEG-1
The average value measured for a long video sequence is a very important number when testing CPU workload because MPEG-4 operates with variable compression and therefore a variable data rate. Therefore the CPU workload depends on the complexity of the respective scene. Fast movements require a higher data rate while scene with less changes are handled with much lower data rates.
The CPU workloads displayed are the average values measured with the previously mentioned four-minute MPEG-4 sequence. The software used for playback was the Divx software codec, which is basically a hacked variation of the Microsoft codec.
The CPU workload with MPEG-1 is about a third of that required for MPEG-4. However the image quality and resolution are much worse and no longer state-of-the-art.
The table above shows the CPU workload for MPEG-1 video. The load is only about 35 percent even with an old Pentium II/400. The fastest processor, AMD’s Athlon 1100, is only loaded by 10 percent during playback.
High CPU Load: Intel Celeron and AMD Duron
The first diagram concerning CPU workload also shows clearly that both AMD’s Duron and Intel’s Celeron are more heavily loaded than the Athlon and Pentium III clocked at the same rate. This is due to the smaller size of the L2 cache in the CPU core of the processors which is especially important during MPEG-4 playback. The same results occur with MPEG-1 playback where Intel and AMD’s less expensive processors (Celeron and Duron) show a higher workload.
This is what the CPU workload on a time scale looks like during playback of an MPEG-4 sequence. A Pentium III/600 was used here as a test platform. The peak workload was a full 93 percent!
CPU workload on a socket 7 system with an AMD K6-II/400: After starting the MPEG-4 video sequence playback, the CPU workload was at 100 percent and flicker-free video display can not be guaranteed.
Summary: Duron has the best Price-to-Performance Ratio
Summing up we can say that the creation of MPEG-4 videos and their playback demands a high-performance CPU. In comparison to the old MPEG-1 format, which allowed even old socket 7 PC systems to playback videos without any frame drops, MPEG-4 is a real challenge for many computers.
The processor itself is subject to the highest workload during MPEG-4 encoding: the conversion of a four-minute MPEG-2 sequence (test object) depended heavily on the used CPU and lasted between 10 minutes (AMD Athlon 1100) and 20 minutes (Intel Celeron 667).
AMD’s Duron 650 has the best price-to-performance ratio, especially because it can be overclocked to 800 MHz without problems and then even beats Intel’s expensive Pentium III/800. Our test results prove this beyond doubt.
At this stage all that remains to be done is to wait until software for MPEG-4 encoding is available which supports the ISSE streaming commands of Intel’s processors with a Coppermine core.
Still, the MPEG-4 video format is one of the hottest topics around. After all, it means that DVD films can be saved on CD-ROM’s without a noticeable loss in quality. Note that we’re not talking about creating a copy: during encoding the data is not duplicated but transformed into a different data format using various computing algorithms. The widespread use of MPEG-4 is just about to begin, but it’s certainly about to have a landslide effect!
Even while many magazines and Internet sites are still discussing MP3, MPEG-4 is well on its way.