Audio/Video

You can easily use ffprobe to extract metadata from a given video file (input.mp4 in this example):

ffprobe -v quiet -show_format -show_streams -print_format json input.mp4

Depending on what info you need, you can also omit -show_streams which doesn’t print detailed codec info for the Audio/Video streams but just general data about the file:

ffprobe -v quiet -show_format -print_format json input.mp4

Example output (without -show-streams):

{
    "format": {
        "filename": "input.mp4",
        "nb_streams": 2,
        "nb_programs": 0,
        "format_name": "mov,mp4,m4a,3gp,3g2,mj2",
        "format_long_name": "QuickTime / MOV",
        "start_time": "0.000000",
        "duration": "11.668500",
        "size": "25045529",
        "bit_rate": "17171378",
        "probe_score": 100,
        "tags": {
            "major_brand": "mp42",
            "minor_version": "0",
            "compatible_brands": "isommp42",
            "creation_time": "2022-10-20T19:00:13.000000Z",
            "location": "+48.1072+011.7441/",
            "location-eng": "+48.1072+011.7441/",
            "com.android.version": "12",
            "com.android.capture.fps": "30.000000"
        }
    }
}

Example output (with -show_streams):

{
    "streams": [
        {
            "index": 0,
            "codec_name": "h264",
            "codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
            "profile": "High",
            "codec_type": "video",
            "codec_tag_string": "avc1",
            "codec_tag": "0x31637661",
            "width": 1920,
            "height": 1080,
            "coded_width": 1920,
            "coded_height": 1080,
            "closed_captions": 0,
            "has_b_frames": 0,
            "pix_fmt": "yuv420p",
            "level": 40,
            "color_range": "tv",
            "color_space": "bt709",
            "color_transfer": "bt709",
            "color_primaries": "bt709",
            "chroma_location": "left",
            "refs": 1,
            "is_avc": "true",
            "nal_length_size": "4",
            "r_frame_rate": "30/1",
            "avg_frame_rate": "10170000/349991",
            "time_base": "1/90000",
            "start_pts": 0,
            "start_time": "0.000000",
            "duration_ts": 1049973,
            "duration": "11.666367",
            "bit_rate": "16914341",
            "bits_per_raw_sample": "8",
            "nb_frames": "339",
            "disposition": {
                "default": 1,
                "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
            },
            "tags": {
                "rotate": "90",
                "creation_time": "2022-10-20T19:00:13.000000Z",
                "language": "eng",
                "handler_name": "VideoHandle",
                "vendor_id": "[0][0][0][0]"
            },
            "side_data_list": [
                {
                    "side_data_type": "Display Matrix",
                    "displaymatrix": "\n00000000:            0       65536           0\n00000001:       -65536           0           0\n00000002:            0           0  1073741824\n",
                    "rotation": -90
                }
            ]
        },
        {
            "index": 1,
            "codec_name": "aac",
            "codec_long_name": "AAC (Advanced Audio Coding)",
            "profile": "LC",
            "codec_type": "audio",
            "codec_tag_string": "mp4a",
            "codec_tag": "0x6134706d",
            "sample_fmt": "fltp",
            "sample_rate": "48000",
            "channels": 2,
            "channel_layout": "stereo",
            "bits_per_sample": 0,
            "r_frame_rate": "0/0",
            "avg_frame_rate": "0/0",
            "time_base": "1/48000",
            "start_pts": 2016,
            "start_time": "0.042000",
            "duration_ts": 558071,
            "duration": "11.626479",
            "bit_rate": "256234",
            "nb_frames": "545",
            "disposition": {
                "default": 1,
                "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
            },
            "tags": {
                "creation_time": "2022-10-20T19:00:13.000000Z",
                "language": "eng",
                "handler_name": "SoundHandle",
                "vendor_id": "[0][0][0][0]"
            }
        }
    ],
    "format": {
        "filename": "input.mp4",
        "nb_streams": 2,
        "nb_programs": 0,
        "format_name": "mov,mp4,m4a,3gp,3g2,mj2",
        "format_long_name": "QuickTime / MOV",
        "start_time": "0.000000",
        "duration": "11.668500",
        "size": "25045529",
        "bit_rate": "17171378",
        "probe_score": 100,
        "tags": {
            "major_brand": "mp42",
            "minor_version": "0",
            "compatible_brands": "isommp42",
            "creation_time": "2022-10-20T19:00:13.000000Z",
            "location": "+48.1072+011.7441/",
            "location-eng": "+48.1072+011.7441/",
            "com.android.version": "12",
            "com.android.capture.fps": "30.000000"
        }
    }
}
u

In order to rotate a video named input.mp4 using ffmpeg, use the following commands:

Rotate by 90° (clockwise)

ffmpeg -i input.mp4 -vf "transpose=1" rotated.mp4

Rotate by 180°

ffmpeg -i input.mp4 -vf "transpose=2" rotated.mp4

Rotate by 270° (clockwise)

This is equivalent to rotating 90° counter-clockwise.

ffmpeg -i input.mp4 -vf "transpose=3" rotated.mp4

In our previous post How to re-encode videos as H.265 & opus using ffmpeg for archival we listed ffmpeg commands to re-encode video files to H.265 for archival purposes.

In many cases, you want to re-encode all files in a directory. The following example command (for Linux shell such as bash) re-encodes every .avi file in the current directory, assuming that all files are non-interlaced (this affects the ffmpeg flags – see our previous post for more details).

for i in *.avi ; do ffmpeg -i "$i" -c:v libx265 -crf 26 -c:a libopus -b:a 56k -frame_duration 60 "${i}.mkv" ; done

From mymovie.avi, this script will produce mymovie.avi.mkv, saving approximately 70% of the filesize (that, of course, depends heavily on the video itself).

You can easily adapt this command to your liking – for example, by encoding .mp4 files instead of .avi or usign a different CRF or audio bitrate. However, in my opinion, these are sane defaults for most video where the focus is to find a compromise between good video quality and file sie.

You can query all parameters using v4l2-ctl‘s --all parameter, for example:

v4l2-ctl --device /dev/video0 --all

fswebcam -r 1920x1080 --png 9 -d /dev/video0 -D 0 test.png

where:

• -r 1920x1080 is the resolution of the image. The camera must support this. In order to see supported resolutions, see How to list USB camera video formats using v4l2-ctl
• --png 9 means output PNG with quality 9. PNG is lossless, so the quality is just the compression factor. 9 means accept higher CPU consumption for slightly smaller filesize.
• -d /dev/video0 means to use the camera in /dev/video0
• -D 0 means no delay before capturing the image
• test.png means: Write the image to test.png.

v4l2-ctl --device /dev/video0 --list-formats-ext