Avconv rotating mpeg4 - video loses quality?

Question

I'm a newbie in video editing on linux and am trying to rotate a video I took with my phone using AVCONV on an Ubuntu 12.04 machine. It all seems to go honky dory except the output is losing quality. The original video is 1920 x 1080 - 30fps - 1:47 long - 270MBI initially attempted converting by running:<code>avconv -i in.mp4 -strict experimental -vf transpose=1 out.mp4</code>After seeing poor results I enforced frame rate, frame size and compression:<code>avconv -i in.mp4 -strict experimental -vf transpose=1 -r 30 -s hd1080 -qcomp 1 out.mp4</code>the resulting video compresses down to 45MB (from 270MB) and is really pixelated. Can you tell me how to avoid this and maintain the original quality of the video? Here's what the converter spits out:<code>avconv version 0.8.16-4:0.8.16-0ubuntu0.12.04.1, Copyright (c) 2000-2014 the Libav developers built on Sep 16 2014 18:33:49 with gcc 4.6.3Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'tractor_powered_cable-car.mp4': Metadata: major_brand : isom minor_version : 0 compatible_brands: isom3gp4 creation_time : 2015-01-01 10:28:17 Duration: 00:01:47.34, start: 0.000000, bitrate: 20145 kb/s Stream #0.0(eng): Video: h264 (High), yuv420p, 1920x1080, 19974 kb/s, PAR 65536:65536 DAR 16:9, 29.99 fps, 90k tbr, 90k tbn, 180k tbc Metadata: creation_time : 2015-01-01 10:28:17 Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16, 155 kb/s Metadata: creation_time : 2015-01-01 10:28:17File 'out.mp4' already exists. Overwrite ? [y/N] Y[buffer @ 0x21940e0] w:1920 h:1080 pixfmt:yuv420p[transpose @ 0x218dcc0] w:1920 h:1080 dir:1 -> w:1080 h:1920 rotation:clockwise vflip:0Output #0, mp4, to 'out.mp4': Metadata: major_brand : isom minor_version : 0 compatible_brands: isom3gp4 creation_time : 2015-01-01 10:28:17 encoder : Lavf53.21.1 Stream #0.0(eng): Video: mpeg4, yuv420p, 1080x1920 [PAR 1:1 DAR 9:16], q=2-31, 200 kb/s, 30 tbn, 30 tbc Metadata: creation_time : 2015-01-01 10:28:17 Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16, 200 kb/s Metadata: creation_time : 2015-01-01 10:28:17Stream mapping: Stream #0:0 -> #0:0 (h264 -> mpeg4) Stream #0:1 -> #0:1 (aac -> aac)Press ctrl-c to stop encodingframe= 3218 fps= 46 q=31.0 Lsize= 44341kB time=107.27 bitrate=3386.3kbits/s dup=1 drop=0 video:41833kB audio:2441kB global headers:0kB muxing overhead 0.150674%</code>Thanks,Shakus

Answer 1

You may have already found your answer but if not, avconv is re-encoding your video as mpeg4 at only 200kbs, but your original was h264 at 20,000kbs. That's a 100x reduction which explains the pixelation and dramatic file size drop. Try using -b:v 19974k which will set the video encoding bitrate to match your source media.