FFMPEG-如何对输入流进行转码，同时切断前几秒的视频和音频

Question

我正在使用ffmpeg将屏幕记录(x11(输入流转码为MP4。我想切断流的前~10秒，这只是一个空白屏幕(这是故意的(。

我知道如何在从mp4转换到另一个mp4时使用ffmpeg修剪视频，但我找不到任何有效的解决方案来处理输入流，同时考虑延迟和音频/视频同步。

这是我当前的代码：

const { spawn } = require('child_process');
const { S3Uploader } = require('./utils/upload');
const MEETING_URL = process.env.MEETING_URL || 'Not present in environment';
console.log(`[recording process] MEETING_URL: ${MEETING_URL}`);
const args = process.argv.slice(2);
const BUCKET_NAME = args[0];
console.log(`[recording process] BUCKET_NAME: ${BUCKET_NAME}`);
const BROWSER_SCREEN_WIDTH = args[1];
const BROWSER_SCREEN_HEIGHT = args[2];
const MEETING_ID = args[3];
console.log(`[recording process] BROWSER_SCREEN_WIDTH: ${BROWSER_SCREEN_WIDTH}, BROWSER_SCREEN_HEIGHT: ${BROWSER_SCREEN_HEIGHT}, TASK_NUMBER: 43`);
const VIDEO_BITRATE = 3000;
const VIDEO_FRAMERATE = 30;
const VIDEO_GOP = VIDEO_FRAMERATE * 2;
const AUDIO_BITRATE = '160k';
const AUDIO_SAMPLERATE = 44100;
const AUDIO_CHANNELS = 2
const DISPLAY = process.env.DISPLAY;
const transcodeStreamToOutput = spawn('ffmpeg',[
'-hide_banner',
'-loglevel', 'error',
// disable interaction via stdin
'-nostdin',
// screen image size
// '-s', `${BROWSER_SCREEN_WIDTH}x${BROWSER_SCREEN_HEIGHT}`,
'-s', '1140x720',
// video frame rate
'-r', `${VIDEO_FRAMERATE}`,
// hides the mouse cursor from the resulting video
'-draw_mouse', '0',
// grab the x11 display as video input
'-f', 'x11grab',
'-i', ':1.0+372,8',
// '-i', `${DISPLAY}`,
// grab pulse as audio input
'-f', 'pulse', 
'-ac', '2',
'-i', 'default',
// codec video with libx264
'-c:v', 'libx264',
'-pix_fmt', 'yuv420p',
'-profile:v', 'main',
'-preset', 'veryfast',
'-x264opts', 'nal-hrd=cbr:no-scenecut',
'-minrate', `${VIDEO_BITRATE}`,
'-maxrate', `${VIDEO_BITRATE}`,
'-g', `${VIDEO_GOP}`,
// apply a fixed delay to the audio stream in order to synchronize it with the video stream
'-filter_complex', 'adelay=delays=1000|1000',
// codec audio with aac
'-c:a', 'aac',
'-b:a', `${AUDIO_BITRATE}`,
'-ac', `${AUDIO_CHANNELS}`,
'-ar', `${AUDIO_SAMPLERATE}`,
// adjust fragmentation to prevent seeking(resolve issue: muxer does not support non seekable output)
'-movflags', 'frag_keyframe+empty_moov+faststart',
// set output format to mp4 and output file to stdout
'-f', 'mp4', '-'
]
);
transcodeStreamToOutput.stderr.on('data', data => {
console.log(`[transcodeStreamToOutput process] stderr: ${(new Date()).toISOString()} ffmpeg: ${data}`);
});
const timestamp = new Date();
const year = timestamp.getFullYear();
const month = timestamp.getMonth() + 1;
const day = timestamp.getDate();
const hour = timestamp.getUTCHours();
console.log(MEETING_ID);
const fileName = `${year}/${month}/${day}/${hour}/${MEETING_ID}.mp4`;
new S3Uploader(BUCKET_NAME, fileName).uploadStream(transcodeStreamToOutput.stdout);
// event handler for docker stop, not exit until upload completes
process.on('SIGTERM', (code, signal) => {
console.log(`[recording process] exited with code ${code} and signal ${signal}(SIGTERM)`);
process.kill(transcodeStreamToOutput.pid, 'SIGTERM');
});
// debug use - event handler for ctrl + c
process.on('SIGINT', (code, signal) => {
console.log(`[recording process] exited with code ${code} and signal ${signal}(SIGINT)`)
process.kill('SIGTERM');
});
process.on('exit', function(code) {
console.log('[recording process] exit code', code);
});

如有任何帮助，我们将不胜感激！

Answer 1

在最后一个输入后添加-ss X以截断前X秒。