On Fri, 15 May 2015 23:04:06 -0500, John L <orionf...@hotmail.com> wrote:
>Backstory: I have a system in place to automagically convert video files to >smaller formats/versions on request to have a sort of "mobile version" for my >father who travels extensively. The purpose is so that he can fit >significantly more videos on his tablet than if they were the high quality >rips. > >It all boils down to: >ffmpeg -i [input-file] -ac 2 -c:v libx264 -c:a libmp3lame -b:v 1024k -preset >fast [output-file] > >I was under the impression everything was hunky dory until I took a bunch of >the shrunken movies on my phone on a roadtrip. A good many of the videos were >as good as can be expected, and nothing was egregiously wrong. However on a >few videos the audio was absolutely atrocious, blown out, clipping, and just >noise from seemingly nowhere. > >One of the worst was Intersteller which was completely unwatchable after the >first two minutes with all the blown out crescendos, pops, cracks, static, and >voices of the deep adulterating the audio stream. All video files affected by >this were 5.1DTS sources, but not all 5.1DTS were affected. > >When talking with my father he said it was a frequent enough occurrence that >he suspected it was just because I had shrunk the file so small and was an >artifact of that. He did confirm that most videos that were affected weren't >as bad as the Interstellar conversion. > > >------------------------------------ >~/testing$ ffmpeg -version >ffmpeg version 2.5.6-0ubuntu0.15.04.1 Copyright (c) 2000-2015 the FFmpeg >developers >built with gcc 4.9.2 (Ubuntu 4.9.2-10ubuntu13) >configuration: --prefix=/usr --extra-version=0ubuntu0.15.04.1 >--build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu >--shlibdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu >--enable-gpl --enable-shared --disable-stripping --enable-avresample >--enable-avisynth --enable-ladspa --enable-libass --enable-libbluray >--enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite >--enable-libfontconfig --enable-libfreetype --enable-libfribidi >--enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame >--enable-libopenjpeg --enable-libopus --enable-libpulse >--enable-libschroedinger --enable-libshine --enable-libspeex --enable-libssh >--enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libwavpack >--enable-libwebp --enable-lib > xvid --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 > --enable-libzvbi --enable-libzmq --enable-frei0r --enable-libvpx > --enable-libx264 --enable-libsoxr --enable-gnut > ls --enable-openal --enable-libopencv --enable-librtmp --enable-libx265 >libavutil 54. 15.100 / 54. 15.100 >libavcodec 56. 13.100 / 56. 13.100 >libavformat 56. 15.102 / 56. 15.102 >libavdevice 56. 3.100 / 56. 3.100 >libavfilter 5. 2.103 / 5. 2.103 >libavresample 2. 1. 0 / 2. 1. 0 >libswscale 3. 1.101 / 3. 1.101 >libswresample 1. 1.100 / 1. 1.100 >libpostproc 53. 3.100 / 53. 3.100 >------------------------------------ > >To troubleshoot I copied out a particularly bad snippet of audio >ffmpeg -i Int*.mkv -vn -c copy -ss 1:30 -t 0:30 inter.dts Yes. That snippet has about 6 tracks. Some of them are clipping (all on their own). >This audio clip is confirmed to be a good 5.1dts stream Good? Well OK -) >ffmpeg -i inter.dts -ac 2 -c libmp3lame inter-test.mp3 >This audio sample has the exact same audio defects as in the shrunken video Correct. All tracks (some of which had reached maximum encodable levels) are now being added/summed into 1 single (now) overloaded stream. Instead, take the 5.1 and _DOWNMIX_ all tracks to a single stereo for the phone/tablet by declaring -acodec xxxx -ac 2. No intermediate steps should be required. Consider also - Do you need pcm_s32le ? pcm_s16le is usual. > _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user
