ffmpeg convert and add silent audio track to an mpeg

Question

I need to remove the B-Frames and also add a silent audio track to an mpeg. This is my source file (mediainfo input.mpg):

General
Complete name                            : input.mpg
Format                                   : MPEG-PS
File size                                : 3.88 MiB
Duration                                 : 4s 0ms
Overall bit rate                         : 8 131 Kbps
Writing library                          : encoded by TMPGEnc (ver. 2.525.64.184)

Video
ID                                       : 224 (0xE0)
Format                                   : MPEG Video
Format version                           : Version 1
Format settings, BVOP                    : Yes
Format settings, Matrix                  : Default
Format settings, GOP                     : M=3, N=9
Duration                                 : 4s 0ms
Bit rate                                 : 8 000 Kbps
Width                                    : 800 pixels
Height                                   : 600 pixels
Display aspect ratio                     : 4:3
Frame rate                               : 30.000 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Compression mode                         : Lossy
Bits/(Pixel*Frame)                       : 0.556
Time code of first frame                 : 00:00:00:00
Time code source                         : Group of pictures header
GOP, Open/Closed                         : Open
GOP, Open/Closed of first frame          : Closed
Stream size                              : 3.80 MiB (98%)
Writing library                          : TMPGEnc 2.525.64.184

I'm trying it with:

ffmpeg -f lavfi -i anullsrc -i input.mpg -c:v mpeg1video -b:v 8000k \
-minrate 8000k -maxrate 8000k -pix_fmt yuv420p -g 9 -acodec mp2 \
-ac 2 -ab 128k -ar 44100 -async 1 -shortest -y out.mpg

mediainfo out.mpg

General
Complete name                            : out.mpg
Format                                   : MPEG-PS
File size                                : 3.96 MiB
Duration                                 : 4s 23ms
Overall bit rate                         : 8 251 Kbps

Video
ID                                       : 224 (0xE0)
Format                                   : MPEG Video
Format version                           : Version 1
Format settings, BVOP                    : No
Format settings, Matrix                  : Default
Format settings, GOP                     : N=9
Duration                                 : 4s 0ms
Bit rate                                 : 8 000 Kbps
Width                                    : 800 pixels
Height                                   : 600 pixels
Display aspect ratio                     : 4:3
Frame rate                               : 30.000 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Compression mode                         : Lossy
Bits/(Pixel*Frame)                       : 0.556
Time code of first frame                 : 00:00:00:00
Time code source                         : Group of pictures header
GOP, Open/Closed                         : Open
GOP, Open/Closed of first frame          : Closed
Stream size                              : 3.80 MiB (96%)

Audio
ID                                       : 192 (0xC0)
Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 2
Duration                                 : 4s 23ms
Bit rate mode                            : Constant
Bit rate                                 : 128 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 44.1 KHz
Compression mode                         : Lossy
Delay relative to video                  : -11ms
Stream size                              : 62.9 KiB (2%)

Unfortunately is the audio duration different to the video duration and there is some "Delay relative to video" of -11ms I found in another post this option:

-af asetpts=PTS+0.011/TB

which gives me this output:

Audio
ID                                       : 192 (0xC0)
Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 2
Duration                                 : 3s 997ms
Bit rate mode                            : Constant
Bit rate                                 : 128 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 44.1 KHz
Compression mode                         : Lossy
Stream size                              : 62.5 KiB (2%)

This one is close but still not my "4s 0ms" what I expected. How can I add a silent audio track with the "absoutly exact" duration? And do I encode the video right?

Answer 1

Try

ffmpeg -f lavfi -i aevalsrc=0|0:d=4.00 -i input.mpg -c:v mpeg1video -b:v 8000k \
-minrate 8000k -maxrate 8000k -pix_fmt yuv420p -g 9 -acodec mp2 \
-ac 2 -ab 128k -ar 44100 -async 1 -shortest -y out.mpg