Miscellaneous Findings II

This is a roundup of miscellaneous things that I’ve found out about (or have rediscovered). I take notes on findings regularly, and I put the findings that translate well to speech on my podcast, Small Findings. The rest (which are often technical findings), I put here. They’re not always written up for maximum comprehension as a blog post, but if anything is hard to understand, please email me if you need clarification.

Extracting audio from a video

ffmpeg -i undefined.ogv -vn -acodec copy out.ogg

Another example:

ffmpeg -i unfortunate-day.mov -vn -acodec copy out.aac

-vn tells ffmpeg to skip video in the output. -acodec tells it to set the audio codec in the output, so that players know how to play it. copy tells it to copy the output to the following file.

You can’t have it convert the audio format while it’s extracting the audio as far as I know. If the audio stream is encoded as ogg, then you can extract ogg. If it’s encoded as AAC, then you can extract AAC.

#audio #video #ffmpeg

“Too many packets” ffmpeg error

When ffmpeg says “Too many packets buffered for output stream 0:1”, it means it literally. You can increase the buffer size with this switch:

-max_muxing_queue_size 1024

(Substitute the size you need.) After that, it may be able to buffer all of the packets.

That argument needs to go before the output file in the command, though, or there will be complaints. This works, for example, but it won’t work if you put max_muxing_queue_size before -i.

ffmpeg -i demo.ogv -max_muxing_queue_size 1024 demo.mp4 





Extracting a still from a video

Use ffmpeg with the -frames:v 1 switch to tell it to grab a single frome and a jpg filename as the output to tell it to write it to an image file.

You can add -ss <seconds into the video> to tell it where in the video to get the frame from. You can specify jpeg quality -qscale:v <2-31>, with 2 being the highest quality.


ffmpeg -ss 0 -i source-images/Video\ Apr\ 17,\ 5\ 49\ 56\ PM.mov -qscale:v 4 -frames:v 1 output.jpg

Links: - name: Stack Overflow url: https://stackoverflow.com/questions/10225403/how-can-i-extract-a-good-quality-jpeg-image-from-an-h264-video-file-with-ffmpeg




Converting video formats

In many cases, it’s sufficient to just pass filenames with different file extensions to ffmpeg, like this:

ffmpeg -i in.ogv out.mp4

It will use the container format corresponding to the file extensions to pick appropriate default encoders. (e.g. libx264 and aac for mp4)

See also: