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• ffmpeg - Audio Issues with TS File

  5 décembre 2020, par MeaningOfLife

  I am new to the world of ffmpeg, so I apologize in advance if this is a stupid question or request.

  


  I'm in the process of trying to convert a .ts file to a h264/mp4. I was able to successfully convert the video, however whenever I go to play the output file, the audio is weird. Most of the audio is only coming through the left channel. I noticed that the audio has multiple channels - 6 to be exact. And there are two audio streams as well. I'm assuming that this has something to do with it, but I am not sure what exactly to put in the command line to fix it.

  


  I was hoping there would be a way to copy the video stream from the mp4 I had already made with ffmpeg, and then replace the audio from that mp4 with the audio from the source ts file - preferably mixed down into regular stereo audio. It is quite a big file, so I would like to not have to convert the video stream again if I don't have to.

  


  Here is the media information from the source video.

  


  General
ID : 1 (0x1)
Complete name : D:\88th Annual Christmas in Rockefeller Center.ts
Format : MPEG-TS
File size : 9.80 GiB
Duration : 2 h 7 min
Overall bit rate mode : Variable
Overall bit rate : 11.0 Mb/s
Law rating : None

Video
ID : 101 (0x65)
Menu ID : 1 (0x1)
Format : MPEG Video
Format version : Version 2
Format profile : Main@High
Format settings : BVOP
Format settings, BVOP : Yes
Format settings, Matrix : Default
Format settings, GOP : Variable
Format settings, picture structure : Frame
Codec ID : 2
Duration : 2 h 7 min
Bit rate mode : Variable
Bit rate : 9 851 kb/s
Maximum bit rate : 80.0 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Active Format Description : Full frame 16:9 image
Frame rate : 29.970 (30000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.159
Time code of first frame : 00:00:00;00
Time code source : Group of pictures header
Stream size : 8.80 GiB (90%)

Audio #1
ID : 102 (0x66)
Menu ID : 1 (0x1)
Format : AC-3
Format/Info : Audio Coding 3
Commercial name : Dolby Digital
Codec ID : 129
Duration : 2 h 7 min
Bit rate mode : Constant
Bit rate : 384 kb/s
Channel(s) : 6 channels
Channel layout : L R C LFE Ls Rs
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Compression mode : Lossy
Delay relative to video : 32 ms
Stream size : 351 MiB (3%)
Language : English
Service kind : Complete Main

Audio #2
ID : 7543 (0x1D77)
Menu ID : 1 (0x1)
Format : AC-3
Format/Info : Audio Coding 3
Commercial name : Dolby Digital
Codec ID : 129
Duration : 2 h 7 min
Bit rate mode : Constant
Bit rate : 192 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Compression mode : Lossy
Delay relative to video : 11 ms
Stream size : 176 MiB (2%)
Language : Spanish
Service kind : Complete Main

Text #1
ID : 101 (0x65)-CC1
Menu ID : 1 (0x1)
Format : EIA-608
Muxing mode : A/53 / DTVCC Transport
Muxing mode, more info : Muxed in Video #1
Duration : 2 h 7 min
Bit rate mode : Constant
Stream size : 0.00 Byte (0%)
CaptionServiceName : CC1

Text #2
ID : 101 (0x65)-1
Menu ID : 1 (0x1)
Format : EIA-708
Muxing mode : A/53 / DTVCC Transport
Muxing mode, more info : Muxed in Video #1
Duration : 2 h 7 min
Bit rate mode : Constant
Stream size : 0.00 Byte (0%)


  


• Removing both leading and trailing silence from m4a files using ffmpeg

  11 juin 2021, par Tejas Shah

  I have an audio file which has both leading and trailing silence and with the following specifics :

  



  Codec : MPEG AAC Audio (mp4a) Channels : Stereo Sample rate : 44100 Hz Bitrate : 253 kbps

  



  I want to remove the silences AND keep the quality intact.

  



  So far I've tried

  



  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 2.m4a 


  



  This is supposed to remove both the leading and trailing silences. 
But for some reason it doesn't remove the trailing silence. This seems to be a recurring problem. Found the following on another forum.

  



  http://ffmpeg-users.933282.n4.nabble.com/How-to-delete-digital-silence-tp4667256p4667356.html

  



  Also, ffmpeg reduces the bitrate to 128kbps. This I could fix by adding -ab 253k and making the command :

  



  ffmpeg -i 1.m4a -af silenceremove=1:0.5:0:1:0.5:0 -ab 253k 3.m4a 


  



  Now the problem is that the trailing silence isn't removed and when I want to process a batch of files I can't use the same bitrate (like 253kbps ) for every file. I'd like to know how VBR could be used for this case.

  



  I know I can use sox and use the silence and reverse features to trim the silences.

  



  http://digitalcardboard.com/blog/2009/08/25/the-sox-of-silence "Example 3 in this post"

  



  But sox has the following problems :

  



  

  1. It can't handle m4a files, I had to convert all files to mp3.

  


  2. When using the silence filter in sox it caps the bitrate at 128kbps.

     



     sox 1.mp3 2.mp3 silence 1 0.5 1% reverse silence 1 0.5 1% reverse


  


  


• ffmpeg failed to seek near the end the of video

  2 novembre 2020, par HanXu

  I have a video with duration 10.00 :

  


  


  $ ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 small.avi

  


  $ 10.000000

  


  


  However, when I want to take a screenshot at the last frame by

  


  


  $ ffmpeg -ss 10.00 -i small.avi -frames:v 1 -q:v 2 -f image2 -y output.jpg

  


  


  It complains that

  


  


  could not seek to position 10.000

  


  


  In fact, even if I try to take screenshot at 9.98s, ffmpeg still fails to seek

  


  


  $ ffmpeg -ss 9.98 -i small.avi -frames:v 1 -q:v 2 -f image2 -y output.jpg

  


  could not seek to position 9.98

  


  


  However, it succeeds for 9.979999s.

  


  Following is the detailed info of my video by running

  


  


  $ ffprobe -v error -i small.avi -show_streams -show_format -print_format json

  


  


  {
    "streams": [
        {
            "index": 0,
            "codec_name": "dvvideo",
            "codec_long_name": "DV (Digital Video)",
            "codec_type": "video",
            "codec_time_base": "1/25",
            "codec_tag_string": "dvsd",
            "codec_tag": "0x64737664",
            "width": 720,
            "height": 576,
            "coded_width": 720,
            "coded_height": 576,
            "has_b_frames": 0,
            "sample_aspect_ratio": "16:15",
            "display_aspect_ratio": "4:3",
            "pix_fmt": "yuv420p",
            "level": -99,
            "chroma_location": "topleft",
            "refs": 1,
            "r_frame_rate": "25/1",
            "avg_frame_rate": "25/1",
            "time_base": "1/25",
            "start_pts": 0,
            "start_time": "0.000000",
            "duration_ts": 250,
            "duration": "10.000000",
            "bit_rate": "28915663",
            "nb_frames": "250",
            "disposition": {
                "default": 0,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0,
                "timed_thumbnails": 0
            }
        },
        {
            "index": 1,
            "codec_name": "pcm_s16le",
            "codec_long_name": "PCM signed 16-bit little-endian",
            "codec_type": "audio",
            "codec_time_base": "1/48000",
            "codec_tag_string": "[1][0][0][0]",
            "codec_tag": "0x0001",
            "sample_fmt": "s16",
            "sample_rate": "48000",
            "channels": 2,
            "bits_per_sample": 16,
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/48000",
            "start_pts": 0,
            "start_time": "0.000000",
            "bit_rate": "1536000",
            "nb_frames": "480256",
            "disposition": {
                "default": 0,
                "dub": 0,
                "original": 0,
                "comment": 0,
                "lyrics": 0,
                "karaoke": 0,
                "forced": 0,
                "hearing_impaired": 0,
                "visual_impaired": 0,
                "clean_effects": 0,
                "attached_pic": 0,
                "timed_thumbnails": 0
            }
        }
    ],
    "format": {
        "filename": "small.avi",
        "nb_streams": 2,
        "nb_programs": 0,
        "format_name": "avi",
        "format_long_name": "AVI (Audio Video Interleaved)",
        "start_time": "0.000000",
        "duration": "10.000000",
        "size": "37948606",
        "bit_rate": "30358884",
        "probe_score": 100,
        "tags": {
            "encoder": "Lavf58.29.100"
        }
    }
}


  


  It seems that there are some mismatching between ffmpeg seeking and the duration of the video ? How to correctly take a screenshot at, say 9.99s ?

  


  Much thanks for any help !