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• How does C language use ffmpeg to send the H.264 network stream packed by RTP to RTMP server ?

  21 décembre 2020, par yanzhang.guo

  My requirement is : listen to the socket, and the monitored data is H.264 video data encapsulated by RTP. I want to push the monitored data from socket to RTMP server directly. What should I do ? Whether can provide a general idea, I use C language to realize.
I found the following two methods on the Internet. Are there corresponding APIs ? In addition, are there other methods ?

  


  Method 1: unpack RTP package, extract H264 data, and push it out with 
ffmpeg API;
Method 2: call ffmpeg API directly to push the data encapsulated by RTP.


  


• How to seamlessly concatenate multiple Opus files together without popping sound ?

  16 février, par Gurdie Derilus

  I have a large PCM file that I've split into N chunks (N being the # of threads), and I encode them in parallel into Opus files with FFmpeg.

  


  Note : All PCM files are 16-bit Little Endian, 2 channels, 48000 sample rate.

  


  I then concatenate the Opus files using FFmpeg's demuxer, but I can hear an audible pop sound between each segment.

  


  Opening this sample file in Audacity reveals the issue :
Notice the introduced pops in opus

  


  I created a simple and short Golang project on Github with a sample PCM file for easy testing. Note, not production code, so obviously not following any best practices here.

  


  #1, I suspected the pops might've been introduced while parallel encoding each PCM file to Opus files. This, however, wasn't the case.
Concatted Opus files vs Separate Opus files image.

  


  #2, using the concat filter works, however it reencodes the files, which is not doable in my case as it's too slow (these files can & do reach up to an hour). I know Opus files are chainable, so I can't imagine why they don't work flawlessly.

  


  #3, I heard that Opus has a 20ms frame size, so I split the file against that frame size, but this made no difference.

  


  chunkSize := largePcmFileStat.Size() / int64(runtime.GOMAXPROCS(0))
chunkSize = int64(roundUpToNearestMultiple(float64(chunkSize), 4))


  


  The entire sample looks like this :

  


  package main

import (
    "context"
    "fmt"
    "io"
    "log"
    "os"
)

func main() {
    // Grab large PCM file
    largePcmFile, err := os.Open("files/full_raw.pcm")
    if err != nil {
        log.Fatalln(err)
    }

    // Split into 2 chunks
    ByteRate := 2
    SampleRate := 48000
    Channels := 2
    Seconds := 20
    chunkSize := Seconds * Channels * SampleRate * ByteRate

    file1, err := encodePcmToOpus(context.TODO(), io.LimitReader(largePcmFile, int64(chunkSize)))
    if err != nil {
        log.Fatalln(err)
    }

    file2, err := encodePcmToOpus(context.TODO(), io.LimitReader(largePcmFile, int64(chunkSize)))
    if err != nil {
        log.Fatalln(err)
    }

    fmt.Println("Check if these play with no defects:", file1)
    fmt.Println("file1:", file1)
    fmt.Println("file2:", file2)
    fmt.Println()

    concatFile, err := concatOpusFiles(context.TODO(), []string{file1, file2})
    if err != nil {
        log.Fatalln(err)
    }

    fmt.Println("concatted file:", concatFile.Name())
}


  


• Adding background audio in FFMPEG, but quieting it if there is sound in another channel

  9 septembre 2021, par Connor Bell

  I'm appending several videos together with FFMPEG. Some of these videos have accompanying audio, and some do not.

  


  I'd like to add music in the background, and have found out how to do so from here. However, I'd like the background music to be (let's say 80%) quieter if there is already audio in that video. Note that all videos have a null audio track, so just checking for the existence of an audio track isn't sufficient.

  


  My current process is :

  


  

  • Take source videos, add a null audio source and upscale (The null audio source is required for ffmpeg-concat to work due to a bug, I think)

  


  • Combine the videos using ffmpeg-concat

  


  


  Preferably, adding the background music should be the third step, as splitting the background music prior to combining the videos sounds more complex, but I may be wrong.