AMD vs. Intel for video encoding with ffmpeg

I’ve always been an AMD guy.  I’ve often thought that the bang for the buck was better with AMD-based systems.  That’s probably still true, as there’s quite a premium to pay for an Intel Core i7 processor versus the AMD Phenom II processors.  But when it comes to real-time video encoding, you need to pack as much CPU horsepower as possible onto a single system bus.  In this context, the Core i7 really won me over.

We were building a system to encode video using a Blackmagic Design Decklink 2.  We need to encode video in real time to a variety of MPEG-2 and MPEG-4 formats and bitrates.  Some of the video is to be written to disk, and some of it is to be streamed over the network via RTP.

My first inclination was to build an AMD-based system, which I based around these components:

MSI 785GM-E65 AM3 AMD 785G HDMI Micro ATX AMD Motherboard
AMD Phenom II X4 945 Deneb 3.0GHz Socket AM3 95W Quad-Core Processor
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)

Approximate cost: $340 (add about $190 for a case, power supply, video card, and hard drive)

We installed two Decklink 2 cards in the system.  With this system, we were able to take two separate HD video sources (1080i, 59.95 fps) and encode each of them to the following formats:

  • 768 Kbps MPEG4/H.264/AAC via RTP
  • 512 Kbps MPEG4/H.264/AAC via RTP
  • 768 Kbps MPEG4/H.264/AAC to disk
  • JPG snapshots once per minute

CPU idle hovered around 25-30%.  This seemed pretty good, but occasionally the CPU load would spike (probably due to additional complexity in the incoming video signal).  This would lead to instability, and the encoding would fall behind the capture until our frame buffers would be tapped out, bringing an end to the real-time encoding.

We decided to give it a go with an Intel Core i7 system, which we built with these components:

Intel Core i7-920 Bloomfield 2.66GHz LGA 1366 130W Quad-Core Processor
MSI X58M LGA 1366 Intel X58 Micro ATX Intel Motherboard
Crucial Ballistix Tracer 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10600)

Approximate cost: $650 (again, add about $190 for a complete system)

This system was unbelievable.  It reports 8 processors to the OS, with the four hyperthreaded cores.  It is a seemingly bottomless well of compute power.

We can run the same set of encodings, and CPU idle is around 40-50%, which gives us more than enough cushion to handle temporary boosts in video complexity.

Phoronix benchmarks give the Core i7 system about a 30% advantage in video encoding speed, which is well in line with what I’ve seen in practice.

I’m sure you could go with faster AMD processors, but at some point, you lose that “sweet spot” of price/performance, and the prices of the processors shoot up quickly, giving incremental performance boosts.  I think that the Core i7 is simply in another league when it comes to video processing.

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