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Outline the differences between -framerate and -r #31

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Outline the differences between -framerate and -r #31

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40 changes: 22 additions & 18 deletions FfmpegInputs.md
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ ffmpeg -start_number 1 -i img.%04d.png foo.mov
```
Would start from frame number img.0001.png

If not defined the end frame will be the last continuous frame in the frame sequence, so if you have a missing frame it will stop there.
If not defined the end frame will be the last continuous frame in the frame sequence, so if you have a missing frame it will stop there.
You can define the number of frames to capture using the `-frames:v` flag.

N.B. In a windows command shell, % has a special meaning, so you may need to escape the "%", by replacing it with %%, or quote it, e.g.:
Expand All @@ -49,31 +49,36 @@ ffmpeg -pattern_type glob -i "img.*.png" foo.mov
```
Will grab all frames that start with img. and end with ".png"



## Frame Rate

The following aliases are defined for framerate values, either `-r` or `-framerate` parameters.
The frame rate of an input image sequence can be specified using the `-framerate` option before the input.
The frame rate can be specified as a decimal number or as a fraction. The following aliases are also defined
for common frame rates:

| ntsc | 30000/1001 | 29.97 fps equivalent. |
| pal | 25| |
| qntsc | 30000/1001 | VCD compliant NTSC |
| qpal | 25 | VCD compliant PAL |
| sntsc | 30000/1001 | square pixel NTSC |
| spal | 25 | square pixel PAL |
| film | 24 | |
| ntsc-film | 24000/1001 | correct 23.98 |
| Alias | Exact value | Description |
| :-------- | :---------- | :------------------- |
| ntsc | 30000/1001 | 29.97 fps equivalent |
| pal | 25 | |
| qntsc | 30000/1001 | VCD compliant NTSC |
| qpal | 25 | VCD compliant PAL |
| sntsc | 30000/1001 | square pixel NTSC |
| spal | 25 | square pixel PAL |
| film | 24 | |
| ntsc-film | 24000/1001 | correct 23.98 |

Is is prefereable to use a fractional rate, or one of the above settings where possible, for example `-r 30000/1001` is the more precise version of 29.97.
It is preferable to use the fractional representation or one of the above aliases for frame rates that aren't a whole number.
For example `-framerate 30000/1001` is more precise than 29.97 and will prevent your video from slowly going out of sync over time.

Other common fractional rates not defined with presets include:
Some other common fractional rates that do not have aliases defined include:

| 60000/1001 | 59.94 fps equiavalent. |
| 60000/1001 | 59.94 fps equivalent |
| 120000/1001 | 119.88 fps equivalent |

If not specified, the default framerate chosen is 25 fps (i.e. pal).
If not specified, the default frame rate chosen is 25 fps (i.e. pal).

TODO Confirm no difference between -r and -framerate. -framerate seems a little more proper.
You may also see `-r` used in some examples. The `-framerate` option is for manually specifying the frame rate for the image2 demuxer (which is responsible for handling image sequence inputs),
whereas `-r` acts more generally on video streams and modifies existing frame rates by regenerating the frame timestamps or duplicating/dropping frames
(depending on if it is used as an input or output option). For input image sequences, you almost always want `-framerate` over `-r`.

## Looping

Expand All @@ -83,4 +88,3 @@ ffmpeg -y -pattern_type glob -loop 1 -framerate ntsc -i "../sourceimages/chip-ch
```

Note, you want to control the number of frames to output, for a long sequence you would put the `-frames:v 100` before the "-i" flag, but here we are putting it before the output, since we want it to apply to the overall looping input, not the input sequence.