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I want to compress an AVI file to MP4 using an h.264 codec. I could not get the same quality. How can I compress it?

Original Video:

Original Video Screen:

FFmpeg console output (ffmpeg -i input.avi):

FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  built on Dec 28 2012 10:03:40 with gcc 4.4.6 20120305 (Red Hat 4.4.6-4)
  configuration: --enable-shared --enable-gpl --enable-version3 --enable-nonfree                                                                                         --enable-pthreads --enable-x11grab --enable-libopencore-amrnb --enable-libopenc                                                                                        ore-amrwb --enable-libdc1394 --enable-libfaac --enable-libmp3lame --enable-libop                                                                                        enjpeg --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libx264                                                                                         --enable-libxvid --enable-zlib --enable-filter=drawtext
  libavutil     50.36. 0 / 50.36. 0
  libavcore      0.16. 1 /  0.16. 1
  libavcodec    52.108. 0 / 52.108. 0
  libavformat   52.93. 0 / 52.93. 0
  libavdevice   52. 2. 3 / 52. 2. 3
  libavfilter    1.74. 0 /  1.74. 0
  libswscale     0.12. 0 /  0.12. 0
[mpeg4 @ 0x626b50] Invalid and inefficient vfw-avi packed B frames detected
Input #0, avi, from 'input.avi':
  Metadata:
    encoder         : VirtualDubMod 1.5.10.2 (build 2542/release)
  Duration: 01:32:38.13, start: 0.000000, bitrate: 2094 kb/s
    Stream #0.0: Video: mpeg4, yuv420p, 720x304 [PAR 1:1 DAR 45:19], 23.98 tbr,                                                                                         23.98 tbn, 23.98 tbc
    Stream #0.1: Audio: ac3, 44100 Hz, 5.1, s16, 384 kb/s
At least one output file must be specified

Test 1

FFmpeg command:

ffmpeg -i input.avi -vcodec libx264 -vpre lossless_slow -crf 25 -acodec libfaac -threads 0 -t 60 1.mp4

Test 1 Screen:

FFmpeg console output (ffmpeg -i 1.mp4)

    FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  built on Dec 28 2012 10:03:40 with gcc 4.4.6 20120305 (Red Hat 4.4.6-4)
  configuration: --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-pthreads --enable-x11grab --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libdc1394 --enable-libfaac --enable-libmp3lame --enable-libopenjpeg --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid --enable-zlib --enable-filter=drawtext
  libavutil     50.36. 0 / 50.36. 0
  libavcore      0.16. 1 /  0.16. 1
  libavcodec    52.108. 0 / 52.108. 0
  libavformat   52.93. 0 / 52.93. 0
  libavdevice   52. 2. 3 / 52. 2. 3
  libavfilter    1.74. 0 /  1.74. 0
  libswscale     0.12. 0 /  0.12. 0
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '1.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    creation_time   : 1970-01-01 00:00:00
    encoder         : Lavf52.93.0
  Duration: 00:01:00.01, start: 0.000000, bitrate: 618 kb/s
    Stream #0.0(und): Video: h264, yuv420p, 720x304 [PAR 1:1 DAR 45:19], 437 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, 5.1, s16, 176 kb/s
    Metadata:
      creation_time   : 1970-01-01 00:00:00
At least one output file must be specified

Test 2

FFmpeg command:

ffmpeg -y -i input.avi -pass 1 -vcodec libx264 -vpre slow -b 2000k -threads 0 -t 60 -f mp4 -an -y /dev/null
ffmpeg -y -i input.avi -pass 2 -vcodec libx264 -vpre slow -b 2000k -threads 0 -t 60 -acodec libfaac -ab 128k -ac 2 2.mp4

Test 2 Screen:

FFmpeg console output (ffmpeg -i 2.mp4)

FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  built on Dec 28 2012 10:03:40 with gcc 4.4.6 20120305 (Red Hat 4.4.6-4)
  configuration: --enable-shared --enable-gpl --enable-version3 --enable-nonfree --enable-pthreads --enable-x11grab --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libdc1394 --enable-libfaac --enable-libmp3lame --enable-libopenjpeg --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid --enable-zlib --enable-filter=drawtext
  libavutil     50.36. 0 / 50.36. 0
  libavcore      0.16. 1 /  0.16. 1
  libavcodec    52.108. 0 / 52.108. 0
  libavformat   52.93. 0 / 52.93. 0
  libavdevice   52. 2. 3 / 52. 2. 3
  libavfilter    1.74. 0 /  1.74. 0
  libswscale     0.12. 0 /  0.12. 0
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '2.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    creation_time   : 1970-01-01 00:00:00
    encoder         : Lavf52.93.0
  Duration: 00:01:00.01, start: 0.000000, bitrate: 1097 kb/s
    Stream #0.0(und): Video: h264, yuv420p, 720x304 [PAR 1:1 DAR 45:19], 1028 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc
    Metadata:
      creation_time   : 1970-01-01 00:00:00
    Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 63 kb/s
    Metadata:
      creation_time   : 1970-01-01 00:00:00
At least one output file must be specified
u1686_grawity
  • 452,512

1 Answers1

75

First of all, install a more recent version of FFmpeg – grab a static build from the download page.

The use of vpre presets (which is a way to set default values for ffmpeg settings, not encoder settings) is not really necessary; you usually want to use the -preset options defined by the encoders.

The reasons you get low output quality are the following, for your two cases respectively:

  1. In the first case you use crf 25, a Constant Rate Factor that's going to give you worse quality than the default for the x264 encoder (which is 23). The CRF controls the quality. Try setting a lower CRF, maybe 20, 18, etc. Here, lower means better quality, but it'll increase the file size. A change of 6 in the CRF gives you twice/half the original average bitrate, roughly speaking.

    You'll have to set a lower CRF because of the generation loss. You're encoding something that was already encoded, so you're again throwing away visual information. That's never good, but if you have to, you're going to have to set a higher quality so as not to remove too much information from the input video.

  2. In the second case you're trying to set a constant bit rate of 2 MBit/s. Your input video roughly has the same bit rate. Now, x264 delivers much better visual quality than an MPEG-4 Visual encoder for the same bitrate, but due to the generation loss, again, you might want to use an even higher bitrate than the original – otherwise you'll end up compressing away too much information.

    Furthermore, constant bitrate encoding might result in some passages looking good, but other parts of the video looking worse. If you don't let the encoder freely choose the amount of bits it wants to spend on something, you're going to sacrifice quality at the expense of knowing the target file size.

    x264 does have a constant bit rate mode, but it's considered inferior to the other encoding methods. Actually, two-pass encoding isn't meant to target optimal quality, so scratch that.

That all being said, try something along the following:

ffmpeg -i input.avi -c:v libx264 -crf 19 -preset slow -c:a libfdk_aac -b:a 192k -ac 2 out.mp4

If libfdk_aac is not available, use this instead:

ffmpeg -i input.avi -c:v libx264 -crf 19 -preset slow -c:a aac -b:a 192k -ac 2 out.mp4

The main quality control knob will be your CRF setting. Experiment with that and use a lower value if you need better quality.

You can also choose the veryslow preset, which will give you better compression, but the encoding will obviously take longer.

If you can't manage to get a decent quality file at a reasonable file size, then you're out of luck. Better keep the original file as-is, without re-encoding. There's no magic "keeping the same quality" tool when you're compressing something that's already compressed.

slhck
  • 228,104
  • If your video is smaller in size after the conversion with two passes, you need to specify a higher bitrate. Try -b:v 3M or more; but I'd recommend using the CRF method instead of the two-pass variant. – slhck Dec 28 '12 at 15:54
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    @AhmetKa Another option is to simply re-mux the streams from AVI container to MP4 container: ffmpeg -i input.avi -c copy -map 0 output.mp4. There is no re-encoding so there is no quality loss. – llogan Dec 28 '12 at 18:24
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    @AhmetKa I should have mentioned that muxing will not always work if the output container format does not support media formats of the input. See Comparison of container formats to get a general idea of what works. – llogan Dec 28 '12 at 21:39
  • Hello again @slhck Crf is not properly. Bitrate, width, height, etc. Can I calculate? –  Dec 30 '12 at 15:42
  • @AhmetKa I'm not sure I understand you. Do you want to be able to calculate the result file size? That's not really possible with CRF since it's variable bit rate. – slhck Dec 30 '12 at 15:43
  • Could not place the same quality video. Different is the quality of videos. I have to write a standard code.

    ffmpeg -i -c copy -t 60 -threads 0 out.avi > http://tny.cz/038284ca ffmpeg -i input.avi -c:v libx264 -crf 19 -preset veryslow -c:a libfaac -b:a 64k -ac 2 -threads 0 -t 60 out.mp4 >http://tny.cz/4bbd4d60

     –  Dec 30 '12 at 16:05
  • @AhmetKa Sorry, I don't understand what you're asking or what the problem is. What is "placing the same quality video" and "writing a standard code"? Please also, rather than showing the console output from the result files, show the actual output when you're encoding the video. – slhck Dec 30 '12 at 16:08
  • @AhmetKa Try using a lower CRF value, maybe 18, 16, 14? The thing is: If you have to re-encode the video, you will lose quality, there's no way around that. Or you will get a big file. – slhck Dec 30 '12 at 16:45
  • @Ahmet If you're willing to get a crazily huge file, you could set a -crf of 0, which is mathematically lossless; but for all practical purposes, a crf of about 18 is the best you're going to get, as slhck suggests – evilsoup Jan 03 '13 at 23:44
  • In Windows, if libaac is not present I think doing the following does not hurt: ffmpeg -i input.avi -c:v libx264 -crf 19 -preset slow -c:a libvo_aacenc -b:a 192k -ac 2 out.mp4 – hyde Jul 17 '14 at 15:44
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    @hyde You should prefer -c:a aac -strict experimental instead of libvo_aacenc, because it delivers better quality. – slhck Jul 17 '14 at 17:27
  • But in Windows I could not get it to work as the codec was missing :( – hyde Jul 17 '14 at 17:40
  • @hyde -c:a aac should always be available because it is built into ffmpeg. If you don't have it, you probably have some really outdated version? – slhck Jul 17 '14 at 17:46
  • So I did ffmpeg -formats to see what options are available and aac was listed there but I encountered an error using -c:a aac. And my ffmpeg build is pretty recent. I think it's something to do with Windows. Windows build miss many features. – hyde Jul 17 '14 at 18:13
  • @hyde But it should not miss this aac feature. Post a new question please, include full command line output, and we'll sort it out. Note that aac is not a format, but an encoder, so check ffmpeg -codecs. – slhck Jul 17 '14 at 19:26
  • "Unrecognized option 'crf'", this is with the latest ffmpeg from github – matteo Dec 05 '15 at 01:27
  • @matteo Did you compile it with --enable-libx264? (See also https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu) – slhck Dec 06 '15 at 17:19
  • @slhck "The vpre option is deprecated" --> still present and not marked as such – Gyan Jun 14 '18 at 05:42
  • @Gyan You're right. I think at the time I had read something to that effect. – slhck Jun 14 '18 at 09:08
  • What's with the advice to grab a more recent version of ffmpeg? The code in the question indicates OP was using a version downloaded the same day as they posted their question. – TylerH Apr 22 '21 at 19:52
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    @TylerH You're right. To be honest, I don't know what I was thinking eight or nine years ago (question is from 2012). In general, we frequently get questions from users using outdated ffmpeg versions, so this was probably meant more as a general advice. – slhck Apr 28 '21 at 08:06
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    You can use nvidia hardware encoder to speed up encoding, if you have compatible hardware -c:v h264_nvenc see https://trac.ffmpeg.org/wiki/HWAccelIntro – themadmax Oct 15 '21 at 14:16