[FFmpeg-devel] Regarding .webm to .mp4 conversion intermittent and slow

[Devyani Godbole]

Hi,

I am trying to convert .webm file that we get from google's Screencastify
to .mp4 file. I need it to be playable using *Windows Media Player.*

I am using a Ubuntu 14.04 container for the same.

I am using the following command:

> ffmpeg -i in.webm -c:v libx264 -crf 20 -c:a aac -strict experimental out.mp4
>
> Following are my observations:
1. The out.mp4 sometimes plays with the windows media player. At the
time when it plays the time for conversion is less and file size is
also normal.
2. Sometimes it just plays a black video. At that time it takes a lot
of time for conversion.The file size in that case is also very high.

It took near about 20 mins to convert a 17MB file. And the output file was
*113MB*!

Following is the output:

ffmpeg version 1.2.6-7:1.2.6-1~trusty1 Copyright (c) 2000-2014 the FFmpeg
> developers
>   built on Apr 26 2014 18:52:58 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
>   configuration: --arch=amd64 --disable-stripping --enable-avresample
> --enable-pthreads --enable-runtime-cpudetect
> --extra-version='7:1.2.6-1~trusty1' --libdir=/usr/lib/x86_64-linux-gnu
> --prefix=/usr --enable-bzlib --enable-libdc1394 --enable-libfreetype
> --enable-frei0r --enable-gnutls --enable-libgsm --enable-libmp3lame
> --enable-librtmp --enable-libopencv --enable-libopenjpeg --enable-libopus
> --enable-libpulse --enable-libschroedinger --enable-libspeex
> --enable-libtheora --enable-vaapi --enable-vdpau --enable-libvorbis
> --enable-libvpx --enable-zlib --enable-gpl --enable-postproc
> --enable-libcdio --enable-x11grab --enable-libx264
> --shlibdir=/usr/lib/x86_64-linux-gnu --enable-shared --disable-static
>   libavutil      52. 18.100 / 52. 18.100
>   libavcodec     54. 92.100 / 54. 92.100
>   libavformat    54. 63.104 / 54. 63.104
>   libavdevice    53.  5.103 / 53.  5.103
>   libavfilter     3. 42.103 /  3. 42.103
>   libswscale      2.  2.100 /  2.  2.100
>   libswresample   0. 17.102 /  0. 17.102
>   libpostproc    52.  2.100 / 52.  2.100
> Input #0, matroska,webm, from '/tmp/Untitled Screencast.webm':
>   Duration: 00:03:28.55, start: 0.000000, bitrate: 683 kb/s
>     Stream #0:0: Video: vp8, yuv420p, 992x672, SAR 1:1 DAR 31:21, 1k fps,
> 1k tbr, 1k tbn, 1k tbc (default)
>     Stream #0:1: Audio: vorbis, 48000 Hz, stereo, fltp (default)
> File '/tmp/2.mp4' already exists. Overwrite ? [y/N] y
> using SAR=1/1
> [libx264 @ 0x7daaa0] MB rate (2604000) > level limit (2073600)
> [libx264 @ 0x7daaa0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
> [libx264 @ 0x7daaa0] profile Constrained Baseline, level 5.2
> [libx264 @ 0x7daaa0] 264 - core 142 r2491 24e4fed - H.264/MPEG-4 AVC codec
> - Copyleft 2003-2014 - http://www.videolan.org/x264.html - options:
> cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1
> psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0
> cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=18
> lookahead_threads=3 sliced_threads=0 nr=0 decimate=1 interlaced=0
> bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=250
> keyint_min=25 scenecut=0 intra_refresh=0 rc=crf mbtree=0 crf=23.0
> qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=0
> Output #0, mp4, to '/tmp/2.mp4':
>   Metadata:
>     encoder         : Lavf54.63.104
>     Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 992x672
> [SAR 1:1 DAR 31:21], q=-1--1, 16k tbn, 1k tbc (default)
>     Stream #0:1: Audio: aac ([64][0][0][0] / 0x0040), 48000 Hz, stereo,
> fltp, 128 kb/s (default)
> Stream mapping:
>   Stream #0:0 -> #0:0 (vp8 -> libx264)
>   Stream #0:1 -> #0:1 (vorbis -> aac)
> Press [q] to stop, [?] for help
> frame=208554 fps=795 q=-1.0 Lsize=  110871kB time=00:03:28.57
> bitrate=4354.5kbits/s dup=202489 drop=0
> video:108118kB audio:1743kB subtitle:0 global headers:0kB muxing overhead
> 0.919457%
> [libx264 @ 0x7daaa0] frame I:835   Avg QP:14.03  size:106129
> [libx264 @ 0x7daaa0] frame P:207719 Avg QP:17.16  size:   106
> [libx264 @ 0x7daaa0] mb I  I16..4: 100.0%  0.0%  0.0%
> [libx264 @ 0x7daaa0] mb P  I16..4:  0.0%  0.0%  0.0%  P16..4:  0.9%  0.0%
> 0.0%  0.0%  0.0%    skip:99.1%
> [libx264 @ 0x7daaa0] coded y,uvDC,uvAC intra: 43.2% 22.5% 20.3% inter:
> 0.1% 0.7% 0.0%
> [libx264 @ 0x7daaa0] i16 v,h,dc,p: 47% 41%  8%  5%
> [libx264 @ 0x7daaa0] i8c dc,h,v,p: 73% 19%  6%  1%
> [libx264 @ 0x7daaa0] kb/s:4246.85
>



-- *Devyani S. Godbole*