trellis | Trellis aims to facilitate text corpus exploration

Tell it which audio you want with -map:

For MP3 the first 1105 samples are decoder delay, leaving 47 samples returned out of 1152. See How to compute the number of extra samples added by LAME or FFMPEG

Remove -framerate 1/5. That's too low of a value for your given -t and it won't work well with fade (image a fade at 0.2 fps). You're only applying that to the first input, while the rest are using the default -framerate 25. Remove it and the image will be visible.

Alternatively, use -framerate 1 for each image input, and add fps=25 after each setsar. It will be significantly faster.

Your ffmpeg is from 2015 and is too old. Try upgrading using SynoCommunity.

You need to use Bit Stream Video Filter for setting h264 metadata.

When a video player plays a video file, it looks for metadata that attached to the video stream (h264 metadata for example).
The H.264 metadata parameters that affects the colors and brightness are: video_format, colour_primaries, transfer_characteris and matrix_coefficients.

If the parameters are not set, there are defaults.
The defaults for low resolution video are "Limited Range" BT.601 (in most player - I am not sure about MAC OS).
The default gamma curve (affects the brightness) is sRGB gamma curve.
The player converts the pixels from YUV color space to RGB (for displaying the video). The conversion formula is done according to the metadata.

Your input video file input.mp4 has H.264 metadata parameters that are far from the default.

We can assume that scale video filter does not change the color characteristics (the filter applies the YUV elements without converting to RGB).

The characteristics of input.mp4 applies BT.2020, and HLG gamma curve, but converted as if they were default (BT.601 and sRGB gamma), so the colors and brightness are very different from what they should have been.

When FFmpeg encodes a video stream, it does not copy the metadata parameters from the input to the output - you need to set the parameters explicitly.

The solution is using a Bit Stream Video Filter for setting the metadata parameters.

Try using the following command:

You have to choose a balance between encoding speed and encoding efficiency.

1. Choose the slowest -preset you have patience for.
2. Choose the highest -crf value that provides an acceptable quality.

See FFmpeg Wiki: H.264 for more info.

If libx264 does not make a small enough file try libx265, but it takes longer to encode.

See FFmpeg Wiki: HEVC/H.265 for more info.

If you have the proper hardware, then you can use NVENC, QuickSync, or some other implementation.

Encoding will be fast, but it will not match the quality per bit provided by libx264 or libx265.

See FFmpeg Wiki: Hardware for more info.

You can set parameters globally with trellis.par.set or pass to the individual plot using the par.settings parameter. trellis.par.get() can be used to get a list of the names of the objects that can be updated.

So for example the following can be used to update specific parameters within a plot

When you say, "the quality of the video becomes pretty bad," I guess you mean your transcoded output video has a lot of block artifacts in it. That's generally because you haven't allocated enough bandwidth to your output video stream. Without enough output bandwidth to play with, the coder quantizes and eliminates higher-frequency stuff so it looks nasty.

You didn't mention what sort of program material you have. But it's worth mentioning this: in material with lots of motion (think James Bond flick) it doesn't save much bandwidth to reduce the frame rate: we're coding the difference between successive frames. The longer you wait between frames, the more differences there are to code (and the harder the motion estimator has to work). If you radically reduce the frame rate (from 24 to 2 for example) it gets much worse.

Talking-heads material is generally less sensitive to framerate.

You might try setting your bandwidth -- your output bitrate -- explicitly like this.

Your linked x264 is too old and therefore has a max level of 5.2 which 6912x3456@30 is past the level limit (as shown by your ffmpeg process output). While exceeding the limit may or may not be the reason for the hang I expect a newer version of x264 will support level 6.0 and will not hang. You have several options:

• Upgrade your x264 (and your ffmpeg while you're at it as the 3.2 branch is from 2016). See the compile guide or download a recent ffmpeg with modern libx264 included.
• Or add the scale filter and try to stay within the level limits: -vf "scale=4096:-2,fps=30,format=yuv420p"
• Or try -c:v libx265 instead of -c:v libx264 (it also has levels to be aware of).
• Or you may have just not waited long enough.