FPS dropping considerably during conversion

[Placebo]

hello guys this is my first thread here...
I know I'm posting a very frequent question, but I tried many different converters still no satisfactory output! please I need your help!
So to start with.. I'm converting a video file to same container but with slightly lower resolution to support it on my mobile phone

General
Unique ID                                : 232250534500425768444268969911738228310 (0xAEB9D36E25264644A151C642C6DCDE56)
Complete name                            :\Downloads\The Thieves.mkv
Format                                   : Matroska
Format version                           : Version 4 / Version 2
File size                                : 500 MiB
Duration                                 : 2h 15mn
Overall bit rate                         : 515 Kbps
Movie name                               : The Thieves 2012 BRRip 480p x264 AAC - VYTO
Encoded date                             : UTC 2010-02-22 21:41:31
Writing application                      : mkvmerge v5.9.0 ('On The Loose') built on Dec  9 2012 15:37:01
Writing library                          : libebml v1.3.0 + libmatroska v1.4.0

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High 10@L4.1
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 8 frames
Muxing mode                              : Header stripping
Codec ID                                 : V_MPEG4/ISO/AVC
Duration                                 : 2h 15mn
Nominal bit rate                         : 457 Kbps
Width                                    : 720 pixels
Height                                   : 304 pixels
Display aspect ratio                     : 2.35:1
Frame rate mode                          : Constant
Frame rate                               : 24.000 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 10 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.087
Writing library                          : x264 core 129 r2230 1cffe9f
Encoding settings                        : cabac=1 / ref=8 / deblock=1:-3:-1 / analyse=0x3:0x133 / me=umh / subme=9 / psy=1 / psy_rd=1.00:2.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-6 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=240 / keyint_min=24 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=2pass / mbtree=1 / bitrate=457 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=81 / qpstep=4 / cplxblur=20.0 / qblur=0.5 / vbv_maxrate=50000 / vbv_bufsize=50000 / nal_hrd=none / ip_ratio=1.40 / aq=1:1.00
Default                                  : Yes
Forced                                   : No

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : HE-AACv2 / HE-AAC / LC
Codec ID                                 : A_AAC
Duration                                 : 2h 15mn
Channel(s)                               : 2 channels / 1 channel / 1 channel
Channel positions                        : Front: L R / Front: C / Front: C
Sampling rate                            : 48.0 KHz / 48.0 KHz / 24.0 KHz
Compression mode                         : Lossy
Language                                 : Korean
Default                                  : Yes
Forced                                   : No

So the original resolution is 720x304 and I'm converting it to a lesser one about 624x272 Keeping rest parameters same.
Everything goes fine .. When I start converision in Handbrake, ffmpeg or ripbot.. Initially I get a decent above 110fps but slowly the fps drops to about 20-10 fps in 10mins... I check the CPU utilization which shows me above 80% in the start but gradually decreases to 40-30%
Why is this happening???
I'm not talking specificallly about this particular conversion ... with other sources also Im getting same problems! I cant take this anymore and Im getting frustrated !
Specs :
Core i3 , 4Gig RAM, 500GB HDD , ATI RADEON GPU.

[smrpix]

Often the start of a movie is something like a logo or a few seconds of black so the encoder can deal with it quickly. But more importantly, your downsize conversion seems insignificant and unnecessary. Is that the only resolution your phone accepts?

[neomaine]

You've also only got an I3, though need more specs to know how low, and you're using a single hard drive. Things would be more streamlined reading from one drive and writing to another. With a single drive, you're trying to read and write at the same time to the same drive.

Look for other posts that describe optimum conversion setups. In general:

- More cores the better.
- Use software that can take advantage of multiple cores.
- Have enough RAM to cover the programs so there's no paging/swaping
- Use separate drives for source and destination to avoid thrashing.
- Don't have other processes running that use the same resources (cpu, disk, ram...) that the conversion software uses.

[jagabo]

Two hard drives will make almost no difference in encoding time when your going from a highly compressed input to a highly compressed output. You easily have enough DRAM to encode SD video. If you don't care too much about quality use an encoder that supports Intel Quick Sync. That's probably your best option. Try the QS mod of Handbrake.

[neomaine]

If the bottleneck is cpu, then I'd agree with you. The reencoding may not hit an i/o threshold where it makes a difference.

But, given any modern cpu with quad core (or more) and an encoder that takes advantage of them, it definitely makes a difference. I don't reencode much these days, disk space is just way too cheap, but find a marked difference when I forget to use separate source/dest drives.

[jagabo]

If the bottleneck is cpu, then I'd agree with you. The reencoding may not hit an i/o threshold where it makes a difference.

With AVC (both input and output) conversion disk I/O is almost never a bottleneck. Using separate source and destination disks might save a few seconds off an hour long encode. Unless the OP is using an old USB 1.1 external hard drive he's not going to significantly improve his performance by using two drives.