30
votes
Accepted
What is KeyInt and min-keyint and no-scenecut
The frames in your H.264 video are grouped into units called GOPs (Group Of Pictures). Inside these GOPs frames are classified into three types:
I-frame: frame that stores the whole picture
P-frame: ...
- 740
25
votes
Accepted
How to fade in/out a video/audio clip with unknown duration?
#1 To simultaneously fade the audio in/out:
ffmpeg -i clip.mp4 -vf 'fade=in:0:30,fade=out:960:30'
-af 'afade=in:st=0:d=1,afade=out:st=32:d=1'
-c:v libx264 -crf 22 -preset ...
- 32.6k
15
votes
How to fade in/out a video/audio clip with unknown duration?
It's a terrible hack, but this might work if all you want to do is audio fade in/out but don't know exactly how long the clip is:
ffmpeg -i input.mp4 -filter_complex "afade=d=0.5, areverse, afade=d=0....
- 251
12
votes
Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly
The usual solution for this situation: -fflags +genpts
It should eliminate the warning, but there's no guarantee your sync issues will be solved.
- 221
10
votes
Accepted
Can video have multiple streams (like it has 2 audio streams)
Yes. MPEG-4 Part 14 (the MP4 container format) supports any number of objects (e.g. video, audio and subtitle streams) and isn't limited to only one stream per content type.
In practice however, you ...
- 5,412
9
votes
Accepted
ffmpeg concat introduces a/v sync problem
Run
ffmpeg -i titlefile.mp4 -vf setdar=16/9 -video_track_timescale 29971 -ac 1 newtitle.mp4
and then run concat with the new title video.
Modern containers like MP4 have Presentation TimeStamps, ...
- 32.6k
8
votes
Accepted
Loudness control LUFS level adjustments
FFmpeg's loudnorm filter can be used. Basic syntax is
ffmpeg -i in.mp4 -c:v copy -af loudnorm=I=-23:LRA=1 -ar 48000 out.mp4
The loudness range (LRA) should be 2 x max deviation.
Also see the ...
- 32.6k
8
votes
Accepted
FFMPEG: Loop video to the length of audio
For video, stream_loop option should be used.
ffmpeg -y -stream_loop -1 -i video -i audio.mp3 -fflags +shortest -max_interleave_delta 50000 -c copy output.mp4
You'll have to use a very recent ...
- 32.6k
7
votes
Accepted
Mono to Stereo using FFMPEG
If you run ffmpeg -layouts, you will see that stereo indicates the presence of two channels, one assigned as Front Left and the other as Front Right. If you use -ac 2 in your encode, ffmpeg will ...
- 32.6k
7
votes
What is KeyInt and min-keyint and no-scenecut
Most video encoders apply temporal compression i.e. most frames only store the difference in image content relative to other frames, thus saving storage space, while a few frames store the whole image....
- 32.6k
6
votes
Accepted
App to quickly analyze audio loudness of several video files?
ffmpeg, a free multi-platform command-line tool, can do this.
Use the volumedetect and EBUR filters on each of the files
ffmpeg -i input.mov -af volumedetect,ebur128 -f null - 2> input.log
This ...
- 32.6k
6
votes
Accepted
Do I need an audio recorder?
Back in the day when movie cameras recorded to film, the sound made by the cameras was something to be isolated from the sound recording process. Digital video cameras make very little noise (with ...
- 4,730
6
votes
How to modify audio level of video according to replaygain info?
FFmpeg, a free command-line tool, has a volume filter that should do this.
Syntax would be
ffmpeg -i input.mp4 -c:v copy -af volume=replaygain=track output.mp4
The af invokes the volume filter with ...
- 32.6k
5
votes
Accepted
Does the MP4 HTML5 compatible video type allow for mono audio?
The Mainconcept or Sony codecs in Vegas are subpar for low-bitrate output such as needed for HTML5 use. Use ffmpeg to generate your HTML5 videos. Yes, mono audio is acceptable for HTML5 use, but once ...
- 32.6k
5
votes
Accepted
Handle 2 sources in a video file
First, get ffmpeg.
Generally, you want to give YouTube the highest quality you can because it will re-encode anything you give it, but the formats used in MXF can be mental for uploading. So re-...
- 9,904
5
votes
Accepted
How to precisely synchronise an audio and video track from separate devices?
First off, if you have audio with your video (that you want to replace with your high-quality audio recording), then step #1 is to nudge the Zoom audio track to line up the impulse of the clap with ...
- 4,730
5
votes
Accepted
By how much can video and audio be out of sync?
There are, in fact, several standards on audio/video or lip sync. The problem is, they can't all agree on what the acceptable error is. What is well understood is that if the audio lags the video it ...
- 2,405
5
votes
Accepted
What is the difference between audio Sampling rate and Frame rate?
Audio samples are encapsulated into frames as well. For PCM, the framing is notional, but for DCT-based codecs, it's a basic requirement.
AAC typically bundles 1024 samples per frame, so 1 second of ...
- 32.6k
5
votes
Accepted
Are most scenes in movies voiced over in post production?
It's generally preferred to use the actual dialog audio from the take. It matches the movement of the lips, it sounds right for the environment, the actor is giving an authentic performance, etc. ...
- 476
4
votes
Accepted
What is the best way to plan and sync voiceover?
In addition to @Mulvya answer I will suggest to use not Flash, but After Effects for animation, if possible. Then you will be able to make Dynamic Link to your AE project. Than will be easier to jump ...
- 1,729
4
votes
Wireless audio from P.A. System to DSLR
There are a lot of variables in this equation, and any one of them could be the culprit. These include: the quality of the audio picked up by the lapel mic, the quality of the PA preamp, the quality ...
- 4,730
4
votes
Increasing Overall Audio level
Yes. You can use FFmpeg, a free command-line tool, like so:
ffmpeg -i video.wmv -c:v copy -af dynaudnorm out.wmv
dynaudnorm is a dynamic audio normalizer, which will maintain the original range ...
- 32.6k
4
votes
Accepted
Do a sort of HEAC - High Efficiency Audio Codec exists?
I think HE-AAC fits that bill.
High-Efficiency Advanced Audio Coding (HE-AAC) is an audio coding
format for lossy data compression of digital audio defined as an
MPEG-4 Audio profile in ISO/IEC ...
- 32.6k
4
votes
Accepted
Why headphones doesn't work with mic out port?
Microphones output at mic level, which is a signal that ranges from around 0.001 volts to 0.01 volts. Headphones work at closer line level, which is around 1 volt. Based off that information, you can ...
- 2,405
4
votes
Using FFMPEG, how does one manage to find the file to convert?
If a filename or its folder has spaces or other special characters, you need to enclose it in quotes i.e.
ffmpeg -i "c:\this\file name\and path\has\spaces in it.mp4" ...
- 32.6k
4
votes
Extract all audio channels as separate wave file from a multichannel file
For me the -map_channel option did the trick:
get the file layout using ffprobe multichannelinputfile.mov
ffprobe version 4.1 Copyright (c) 2007-2018 the FFmpeg developers
built with Apple LLVM ...
- 41
4
votes
Error converting mp4 to matroska format
Your ffmpeg is outdated. Update and it will automatically insert some bitstream filters (at least aac_adtstoasc, hevc_mp4toannexb, h264_mp4toannexb). According to the aac_adtstoasc documentation:
...
- 9,904
4
votes
Accepted
Disguising the identity of a voice over
You have a few options for disguising a voice, but several of them intentionally make the sound unnatural.
Have someone else record the voiceover. This is the only technique that results in a truly ...
- 2,405
4
votes
Accepted
Timestamps are unset in a packet for stream 0. This is deprecated and will stop working in the future. Fix your code to set the timestamps properly
this worked for me as an option to ffmpeg: -use_wallclock_as_timestamps 1
- 323
4
votes
Decreasing levels of other channels when voice channel comes in
"Ducking" is the canonical term for what you want, usually done with a compressor in the main program chain with the sidechain taken from your mic channel.
Audition 2018 has a auto ducking feature ...
- 211
Only top scored, non community-wiki answers of a minimum length are eligible