title: Converting from FLV to MP4 using ffmpeg
body: <p>I have a library of several thousand flv files which I need to convert to mp4. I'm trying to use ffmpeg to do so but I'm running into some issues. </p>
  
  <p>Primarily:</p>
  
  <p>1) I can't switch from FLV to MP4 without re-encoding. If I do I get a message from ffmpeg saying "Could not find tag for codec flv1 in stream #0, codec not currently supported in container"</p>
  
  <p>2) If I re-encode the videos, the resultant videos are lower quality (I see artifacting in VLC) AND larger. For example one video went from 2.5MB to 4.3MB (almost double in size)</p>
  
  <p>Given number two you may be asking yourself - why convert then? </p>
  
  <p>The answer is I need to stream these to mobile devices (phones/tablets etc) and flv isn't supported. So I need to convert the files but I can't tolerate more than a minimum change in quality, and preferably zero to no increase in size. </p>
  
  <p>Here's the ffmpeg command I'm running:</p>
  
  <pre><code>ffmpeg -i $_.FullName -movflags faststart -profile:v baseline -level 3.0 "$($_.BaseName).mp4"
  </code></pre>
  
  <p>(Note that I'm running ffmpeg from powershell so: </p>
  
  <pre><code>$_.FullName = the original file name 
  "$($_.BaseName).mp4" = the original file name with mp4 extension)
  </code></pre>
  
  <p>Can any FFMPEG guru's help me to understand what I'm doing wrong? Is there some set of parameters I can use to make this conversion result in less loss of quality and similar size?</p>
  
  <p>Note I've also tried "-c:v libx264 -preset veryslow -crf 23 -c:a copy". Using present "veryslow" doesn't result in any appreciable difference.</p>
  
  <p><strong><em>UPDATE</em></strong>
  I'm using the following options:</p>
  
  <pre><code>ffmpeg -i $_.FullName -c:v libx264 -preset veryslow -crf 19 -c:a copy "$($_.BaseName).mp4"
  </code></pre>
  
  <p>Here's the full output:</p>
  
  <pre>
  
  
      ffmpeg version 2.8.4 Copyright (c) 2000-2015 the FFmpeg developers
        built with gcc 5.2.0 (GCC)
        configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfi
      g --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
      enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libm
      p3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
      able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --ena
      ble-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enabl
      e-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
        libavutil      54. 31.100 / 54. 31.100
        libavcodec     56. 60.100 / 56. 60.100
        libavformat    56. 40.101 / 56. 40.101
        libavdevice    56.  4.100 / 56.  4.100
        libavfilter     5. 40.101 /  5. 40.101
        libswscale      3.  1.101 /  3.  1.101
        libswresample   1.  2.101 /  1.  2.101
        libpostproc    53.  3.100 / 53.  3.100
      Input #0, flv, from 'C:\Users\brad\Desktop\ffmpeg\Originals\1019800-1278575542468.flv':
        Metadata:
          canSeekToEnd    : false
          createdby       : FMS 3.5
          creationdate    : Thu Jul 08 03:52:25 2010
        Duration: 00:00:56.94, start: 0.000000, bitrate: 360 kb/s
          Stream #0:0: Video: flv1, yuv420p, 320x240, 1k tbr, 1k tbn, 1k tbc
          [libx264 @ 02cf7300] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
          [libx264 @ 02cf7300] profile High, level 4.2
          [libx264 @ 02cf7300] 264 - core 148 r2638 7599210 - H.264/MPEG-4 AVC codec - Copyleft 2003-2015 - http://www.videolan.or
      g/x264.html - options: cabac=1 ref=16 deblock=1:0:0 analyse=0x3:0x133 me=umh subme=10 psy=1 psy_rd=1.00:0.00 mixed_ref=1
       me_range=24 chroma_me=1 trellis=2 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=7 lookahead_th
      reads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=8 b_pyramid=2 b_adapt=
      2 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=60
      rc=crf mbtree=1 crf=19.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
      Output #0, mp4, to '1019800-1278575542468.mp4':
        Metadata:
          canSeekToEnd    : false
          createdby       : FMS 3.5
          creationdate    : Thu Jul 08 03:52:25 2010
          encoder         : Lavf56.40.101
          Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 320x240, q=-1--1, 1k fps, 16k tbn, 1k tbc
          Metadata:
            encoder         : Lavc56.60.100 libx264
      Stream mapping:
        Stream #0:0 -> #0:0 (flv1 (flv) -> h264 (libx264))
      Press [q] to stop, [?] for help
      frame=57117 fps=199 q=-1.0 Lsize=    5611kB time=00:00:57.11 bitrate= 804.8kbits/s dup=56685 drop=0
      video:5184kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 8.229259%
      [libx264 @ 02cf7300] frame I:230   Avg QP:15.92  size:  8828
      [libx264 @ 02cf7300] frame P:6399  Avg QP:17.19  size:   385
      [libx264 @ 02cf7300] frame B:50488 Avg QP:27.13  size:    16
      [libx264 @ 02cf7300] consecutive B-frames:  0.4%  0.0%  0.0%  0.0%  0.0%  2.3%  0.0%  0.0% 97.2%
      [libx264 @ 02cf7300] mb I  I16..4:  2.9% 92.6%  4.5%
      [libx264 @ 02cf7300] mb P  I16..4:  0.1%  2.0%  0.2%  P16..4:  2.4%  1.2%  1.1%  0.1%  0.0%    skip:92.9%
      [libx264 @ 02cf7300] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  2.6%  0.0%  0.0%  direct: 0.0%  skip:97.3%  L0:45.0% L1:5
  4.9% BI: 0.0%
      [libx264 @ 02cf7300] 8x8 transform intra:90.7% inter:76.5%
      [libx264 @ 02cf7300] direct mvs  spatial:75.2% temporal:24.8%
      [libx264 @ 02cf7300] coded y,uvDC,uvAC intra: 94.4% 96.8% 64.8% inter: 0.3% 0.4% 0.1%
      [libx264 @ 02cf7300] i16 v,h,dc,p: 16% 25% 18% 41%
      [libx264 @ 02cf7300] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 28% 30%  4%  3%  3%  4%  4%  5%
      [libx264 @ 02cf7300] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 18% 22%  9% 11%  8%  7% 10%  8%  7%
      [libx264 @ 02cf7300] i8c dc,h,v,p: 30% 34% 23% 13%
      [libx264 @ 02cf7300] Weighted P-Frames: Y:0.1% UV:0.1%
      [libx264 @ 02cf7300] ref P L0: 74.1% 19.7%  4.5%  0.6%  0.1%  0.2%  0.0%  0.1%  0.0%  0.1%  0.0%  0.2%  0.0%  0.2%  0.0%
    0.1%
      [libx264 @ 02cf7300] ref B L0: 95.5%  1.6%  0.7%  0.5%  0.4%  0.3%  0.3%  0.2%  0.1%  0.1%  0.1%  0.1%  0.1%  0.0%  0.0%
  
      [libx264 @ 02cf7300] ref B L1: 84.5% 15.5%
      [libx264 @ 02cf7300] kb/s:743.46
  
  </pre>
  
  <pre><code>Original Video Size: 2.44 MB
  New Video Size: 5.6 MB
  </code></pre>