How do I synchronize audio with video in an MP4 file?

[ilyaz]

Hello Everyone!

First post here. I have an MP4 file which has a digitized home video shot using a PAL camcorder in late 80s. When I play it with VLC or RealPlayer, I notice right away that audio and video are not synchronized. Here's what ffplay reports about it:

ffplay.exe file.mp4

ffplay version git-2020-04-13-59e3a9a Copyright (c) 2003-2020 the FFmpeg developers
built with gcc 9.3.1 (GCC) 20200328
configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libsrt --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
libavutil 56. 42.102 / 56. 42.102
libavcodec 58. 78.102 / 58. 78.102
libavformat 58. 42.100 / 58. 42.100
libavdevice 58. 9.103 / 58. 9.103
libavfilter 7. 77.101 / 7. 77.101
libswscale 5. 6.101 / 5. 6.101
libswresample 3. 6.100 / 3. 6.100
libpostproc 55. 6.100 / 55. 6.100

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 2019-07-14T15:59:21.000000Z
encoder : Lavf57.57.100
Duration: 01:02:57.88, start: 0.000000, bitrate: 3622 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x576 [SAR 12:11 DAR 15:11], 3504 kb/s, SAR 16:15 DAR 4:3, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
Metadata:
creation_time : 2019-07-14T15:59:21.000000Z
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 111 kb/s (default)
Metadata:
creation_time : 2019-07-14T15:59:21.000000Z
handler_name : SoundHandler
SDL_OpenAudio (2 channels, 48000 Hz): WASAPI can't initialize audio client: CoInitialize has not been called.

SDL_OpenAudio (1 channels, 48000 Hz): WASAPI can't initialize audio client: CoInitialize has not been called.

SDL_OpenAudio (2 channels, 44100 Hz): WASAPI can't initialize audio client: CoInitialize has not been called.

SDL_OpenAudio (1 channels, 44100 Hz): WASAPI can't initialize audio client: CoInitialize has not been called.

No more combinations to try, audio open failed
24.49 M-V: -0.017 fd= 1 aq= 0KB vq= 470KB sq= 0B f=0/0

What do I need to do to synchronize the two streams? TIA!

[daigo99]

You can use ffmpeg to offset the audio on an mp4:

ffmpeg.exe -i file.mp4 -itsoffset 0.00 -i file.mp4 -map 0:v -map 1:a -c copy Adjustedfile.mp4

the -itsoffset 0.00 needs to be changed to reflect how much you want to offset.
Use the "j" or "k" keys while playing the video in VLC player to find out by how much.

[ilyaz]

Thank you! Worked like a charm. -850ms offset. Curious why this number...

[Gartons]

This is the most frequent disadvantage of this camera. In addition, this video is old. This error also may occur when audio and video were synchronized incorrectly. You can try to redo them with the help of special programs or contact qualified specialists. By the way, I often use video and audio from youtube when I edit. I apply third-party software for it. If you are interested, you should take a look here. Moreover, I use this software to convert favorite mixes into a suitable layout.