title: FFMPEG Cutting Commercials puts audio out of sync
body: <p>Ubuntu 14.04.1 with the real ffmpeg loaded (same problem with the avconv version).</p>
  
  <p>I'm trying to take files created in MythTV with a HDPVR, cut the commercials and put the video into an MP4 container for use with MythRoku.</p>
  
  <p>the command</p>
  
  <p><code>ffmpeg -i $file -acodec copy -vcodec copy -f mp4 file.mp4</code></p>
  
  <p>Works fine. Once I update the database, I can watch the file in MythRoku or Plex.</p>
  
  <p>However, when I try to cut out the commercials, the audio gets out of sync by just over 1 second (audio delayed) whenever I cut past the 0 mark.  Totem Video player and VLC both play the resulting video fine, but I can see a "hitch" at the beginning while they are syncing the audio, so I know the information on the audio sync is in the file somewhere.  Mythroku and Plex both are out of sync when playing the file.  The MythTV Frontend player actually does play it correctly, and I can hear the "hitch" as it syncs the audio.</p>
  
  <p>After hours of reading posts and playing with settings, I've got it down to this:</p>
  
  <p>If I say:</p>
  
  <p><code>ffmpeg -i $file -acodec copy -vcodec copy -f mp4 -ss 0 -t &lt;anything&gt; out.mp4</code></p>
  
  <p>The file is fine, plays both locally and in MythRoku/Plex</p>
  
  <p>But if I advance the start any amount - even 1 second - audio is out of sync</p>
  
  <p><code>ffmpeg -i $file -acodec copy -vcodec copy -f mp4 -ss 1 -t &lt;anything&gt; out.mp4</code></p>
  
  <p>I've tried splitting the video (as mp4) and audio (as ac3) first, splitting them separately, and then putting them back together as the last step, but I get the same results.</p>
  
  <p>The information is in the file - Totem, VLC and the Frontend all can figure it out.  How can I get ffmpeg to figure out the sync and write the file so it's correct?</p>
  
  <p>Original file:</p>
  
  <pre><code>mythtv@marvin:~$ mediainfo /var/lib/mythtv/recordings/2225_20140824001500.mpg
  General
  ID                                       : 0 (0x0)
  Complete name                            :     /var/lib/mythtv/recordings/2225_20140824001500.mpg
  Format                                   : MPEG-TS
  File size                                : 4.03 GiB
  Duration                                 : 1h 45mn
  Overall bit rate mode                    : Variable
  Overall bit rate                         : 5 491 Kbps
  
  Video
  ID                                       : 4113 (0x1011)
  Menu ID                                  : 1 (0x1)
  Format                                   : AVC
  Format/Info                              : Advanced Video Codec
  Format profile                           : Main@L4.0
  Format settings, CABAC                   : Yes
  Format settings, ReFrames                : 4 frames
  Format settings, GOP                     : M=4, N=32
  Codec ID                                 : 27
  Duration                                 : 1h 45mn
  Bit rate mode                            : Variable
  Bit rate                                 : 4 831 Kbps
  Maximum bit rate                         : 20.0 Mbps
  Width                                    : 1 280 pixels
  Height                                   : 720 pixels
  Display aspect ratio                     : 16:9
  Frame rate                               : 59.940 fps
  Color space                              : YUV
  Chroma subsampling                       : 4:2:0
  Bit depth                                : 8 bits
  Scan type                                : Progressive
  Bits/(Pixel*Frame)                       : 0.087
  Stream size                              : 3.55 GiB (88%)
  Color primaries                          : BT.709
  Transfer characteristics                 : BT.709
  Matrix coefficients                      : BT.709
  
  Audio
  ID                                       : 4352 (0x1100)
  Menu ID                                  : 1 (0x1)
  Format                                   : AC-3
  Format/Info                              : Audio Coding 3
  Mode extension                           : CM (complete main)
  Format settings, Endianness              : Big
  Codec ID                                 : 129
  Duration                                 : 1h 45mn
  Bit rate mode                            : Constant
  Bit rate                                 : 384 Kbps
  Channel(s)                               : 2 channels
  Channel positions                        : Front: L R
  Sampling rate                            : 48.0 KHz
  Bit depth                                : 16 bits
  Compression mode                         : Lossy
  Delay relative to video                  : -6ms
  Stream size                              : 289 MiB (7%)
  </code></pre>
  
  <p>File cut from 0:</p>
  
  <pre><code>mythtv@marvin:~$ mediainfo 2225_20140824001500_1.mp4
  General
  Complete name                            : 2225_20140824001500_1.mp4
  Format                                   : MPEG-4
  Format profile                           : Base Media
  Codec ID                                 : isom
  File size                                : 58.5 MiB
  Duration                                 : 1mn 45s
  Overall bit rate mode                    : Variable
  Overall bit rate                         : 4 676 Kbps
  Writing application                      : Lavf54.63.104
  
  Video
  ID                                       : 1
  Format                                   : AVC
  Format/Info                              : Advanced Video Codec
  Format profile                           : Main@L4.0
  Format settings, CABAC                   : Yes
  Format settings, ReFrames                : 4 frames
  Format settings, GOP                     : M=4, N=32
  Codec ID                                 : avc1
  Codec ID/Info                            : Advanced Video Coding
  Duration                                 : 1mn 45s
  Bit rate mode                            : Variable
  Bit rate                                 : 4 281 Kbps
  Maximum bit rate                         : 20.0 Mbps
  Width                                    : 1 280 pixels
  Height                                   : 720 pixels
  Display aspect ratio                     : 16:9
  Frame rate mode                          : Variable
  Frame rate                               : 59.940 fps
  Minimum frame rate                       : 59.920 fps
  Maximum frame rate                       : 59.960 fps
  Color space                              : YUV
  Chroma subsampling                       : 4:2:0
  Bit depth                                : 8 bits
  Scan type                                : Progressive
  Bits/(Pixel*Frame)                       : 0.077
  Stream size                              : 53.6 MiB (92%)
  Color primaries                          : BT.709
  Transfer characteristics                 : BT.709
  Matrix coefficients                      : BT.709
  
  Audio
  ID                                       : 2
  Format                                   : AC-3
  Format/Info                              : Audio Coding 3
  Mode extension                           : CM (complete main)
  Format settings, Endianness              : Big
  Codec ID                                 : ac-3
  Duration                                 : 1mn 45s
  Bit rate mode                            : Constant
  Bit rate                                 : 384 Kbps
  Channel(s)                               : 2 channels
  Channel positions                        : Front: L R
  Sampling rate                            : 48.0 KHz
  Bit depth                                : 16 bits
  Compression mode                         : Lossy
  Stream size                              : 4.81 MiB (8%)
  </code></pre>
  
  <p>File cut from 1 second with audio sync problem:</p>
  
  <pre><code>mythtv@marvin:~$ mediainfo 2225_20140824001500_2.mp4
  General
  Complete name                            : 2225_20140824001500_2.mp4
  Format                                   : MPEG-4
  Format profile                           : Base Media
  Codec ID                                 : isom
  File size                                : 68.0 MiB
  Duration                                 : 2mn 0s
  Overall bit rate mode                    : Variable
  Overall bit rate                         : 4 750 Kbps
  Writing application                      : Lavf54.63.104
  
  Video
  ID                                       : 1
  Format                                   : AVC
  Format/Info                              : Advanced Video Codec
  Format profile                           : Main@L4.0
  Format settings, CABAC                   : Yes
  Format settings, ReFrames                : 4 frames
  Format settings, GOP                     : M=4, N=32
  Codec ID                                 : avc1
  Codec ID/Info                            : Advanced Video Coding
  Duration                                 : 1mn 58s
  Bit rate mode                            : Variable
  Bit rate                                 : 4 394 Kbps
  Maximum bit rate                         : 20.0 Mbps
  Width                                    : 1 280 pixels
  Height                                   : 720 pixels
  Display aspect ratio                     : 16:9
  Frame rate mode                          : Variable
  Frame rate                               : 59.940 fps
  Minimum frame rate                       : 59.920 fps
  Maximum frame rate                       : 59.960 fps
  Color space                              : YUV
  Chroma subsampling                       : 4:2:0
  Bit depth                                : 8 bits
  Scan type                                : Progressive
  Bits/(Pixel*Frame)                       : 0.080
  Stream size                              : 62.3 MiB (92%)
  Color primaries                          : BT.709
  Transfer characteristics                 : BT.709
  Matrix coefficients                      : BT.709
  
  Audio
  ID                                       : 2
  Format                                   : AC-3
  Format/Info                              : Audio Coding 3
  Mode extension                           : CM (complete main)
  Format settings, Endianness              : Big
  Codec ID                                 : ac-3
  Duration                                 : 2mn 0s
  Bit rate mode                            : Constant
  Bit rate                                 : 384 Kbps
  Channel(s)                               : 2 channels
  Channel positions                        : Front: L R
  Sampling rate                            : 48.0 KHz
  Bit depth                                : 16 bits
  Compression mode                         : Lossy
  Stream size                              : 5.49 MiB (8%)
  </code></pre>