- I've read that the way to reduce the size of mp4 files is by lowering the video bit rate. So I'm using avconv to do this. The following is the command I'm using:
avconv -i input-file.mp4 -b:v 300k output-file.mp4
So in the above example, say input-file.mp4 has a video bit rate of 1600 kb/s, then the command should produce output-file.mp4 with a video bit rate of 300 kb/s.
- Well, the command runs, but with the following effects:
a) input-file.mp4 is 500 MB in size, but after 8 minutes, output-file.mp4 had reached only 45 MB in size. At that rate, it would take 1 hour 30 minutes to complete! So I aborted the run.
b) The laptop fan ran noticeably louder, and was blowing air out that was much hotter than normal.
c) There is a cpu usage monitor on the status bar at the bottom of the screen. In normal use, this shows a moving green waveform that takes up only a slight to moderate amount of the black background. Whereas when running the said avconv command, the entire black background was obliterated with solid green!
- My Questions:
a) Is there a faster way to do the bit rate lowering?
b) Why is the fan working so hard; why is the air that's being blown out so hot; and how do I stop it happening?
c) Do the same things happen on your computer when you run this avconv command?
My laptop is an Acer Aspire 5755G, i5, with 8 GB of RAM, running Knoppix 7.7.1 from a memory stick (which works fine for all my other uses).
The following shows parts of the output from the following command that I think might be relevant. The "ME:" entries are my own notes. (SORRY, THE QUESTION SUBMISSION THING WOULDN'T LET ME FORMAT IT AS A CODE SAMPLE.) :
$ time avconv -i input-file.mp4 -b:v 300k output-file.mp4
Input #0 ...
network : BBC One
Duration: 00:44:13.04, start: 0.000000, bitrate: 1699 kb/s Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt470bg), 960x540 [SAR 1:1 DAR 16:9], 1599 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc (default)
[ME: I think the "1599 kb/s" above is the bitrate (of input-file.mp4).]
Stream #0:2: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 192x108
[SAR 72:72 DAR 16:9], 90k tbr, 90k tbn, 90k tbc
[libx264 @ 0x8192320] using SAR=1/1
[libx264 @ 0x8192320] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
[ME: The "cpu capabilities" just above might mean something.]
Output #0, mp4, to 'output-file.mp4':
network : BBC One
encoder : Lavf57.41.100
Stream #0:0(und): Video: h264 (libx264) ( / 0x0021), yuv420p, 960x540 [SAR 1:1 DAR 16:9], q=-1--1, 300 kb/s, 25 fps, 12800 tbn, 25 tbc (default)
[ME: I think the "300 kb/s" just above shows that it IS converting it to 300 kb/s bitrate.]
ME: I aborted the run after about 8m30s (CTRL+C). The following is the output just before, and during the abort. I think the messg "Exiting normally, received signal 2." is in response to the CTRL+C:
frame=14350 fps= 43 q=39.0 size= 30338kB time=00:09:34.12 bitrate= 432.9kbits/s dup=1 drop=0 speed= 1.7x frame=14377 fps= 43 q=38.0 size= 30376kB time=00:09:35.18 bitrate= 432.6kbits/s dup=1 drop=0 speed=1.71x frame=20872 fps= 40 q=-1.0 Lsize= 45648kB time=00:13:55.02 bitrate= 447.8kbits/s dup=1 drop=0 speed=1.62x
video:31838kB audio:13194kB subtitle:0kB other streams:0kB global headers:0kB
muxing overhead: 1.367074%
[libx264 @ 0x8192320] frame I:378 Avg QP:30.76 size: 9510
[libx264 @ 0x8192320] frame P:6226 Avg QP:35.29 size: 2581
[libx264 @ 0x8192320] frame B:14268 Avg QP:37.13 size: 907
[libx264 @ 0x8192320] consecutive B-frames: 6.7% 4.4% 5.9% 83.0%
[libx264 @ 0x8192320] mb I I16..4: 33.2% 60.3% 6.5%
[libx264 @ 0x8192320] mb P I16..4: 9.1% 16.7% 0.3% P16..4: 23.7% 2.1% 0.7% 0.0% 0.0% skip:47.5%
[libx264 @ 0x8192320] mb B I16..4: 0.7% 0.8% 0.0% B16..8: 24.9% 0.8% 0.0% direct: 0.2% skip:72.5% L0:42.8% L1:56.4% BI: 0.8%
[libx264 @ 0x8192320] final ratefactor: 34.50
[libx264 @ 0x8192320] 8x8 transform intra:62.5% inter:93.0%
[libx264 @ 0x8192320] coded y,uvDC,uvAC intra: 15.2% 32.0% 1.7% inter: 2.2% 2.5% 0.0%
[libx264 @ 0x8192320] i16 v,h,dc,p: 35% 29% 8% 29%
[libx264 @ 0x8192320] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 10% 51% 3% 3% 3% 3% 3% 2%
[libx264 @ 0x8192320] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 31% 20% 16% 5% 7% 7% 6% 5% 3%
[libx264 @ 0x8192320] i8c dc,h,v,p: 78% 9% 11% 2%
[libx264 @ 0x8192320] Weighted P-Frames: Y:2.7% UV:1.9%
[libx264 @ 0x8192320] ref P L0: 64.6% 13.5% 15.9% 5.8% 0.1%
[libx264 @ 0x8192320] ref B L0: 91.8% 6.5% 1.7%
[libx264 @ 0x8192320] ref B L1: 97.5% 2.5%
[libx264 @ 0x8192320] kb/s:312.40
[aac @ 0x8193840] Qavg: 645.192
Exiting normally, received signal 2.