FFmpegSource2 Avisynth User Manual

Opens files using FFmpeg and nothing else. May be frame accurate on good days. The source is MIT licensed and can be obtained from https://github.com/FFMS/ffms2/. The precompiled binary is GPL3 licensed. If you are religious you may consider this the second coming.

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Donate if you like this software. Collecting weird clips from the internet and making them play takes more time than you'd think.

Limitations

Because of LAVF's demuxer, most raw streams (such as elementary h264 and other mpeg video streams) will fail to work properly.
FFAudioSource() will have to remake any index implicitly created by FFVideoSource() and therefore code like
```
AudioDub(FFVideoSource(X), FFAudioSource(X))
```
will require two indexing passes. Apart from the time consumed this is harmless. To work around it open the audio first:
```
A = FFAudioSource(X)
V = FFVideoSource(X)
AudioDub(V, A)
```
or use FFIndex(), like so:
```
FFIndex(X)
AudioDub(FFVideoSource(X), FFAudioSource(X))
```
Interlaced H.264 mostly works these days, but seeking may occasionally result in corruption.
Transport Streams will not decode reliably without seekmode -1.
Open-GOP H.264 will sometimes produces corruption when seeking.

Compatibility

Video

AVI, MKV, MP4, FLV: Frame accurate
WMV: Frame accurate(?) but avformat seems to pick keyframes relatively far away
OGM: Frame accurate(?)
VOB, MPG: Seeking seems to be off by one or two frames now and then
M2TS, TS: Seeking seems to be off a few frames here and there
Image files: Most formats can be opened if seekmode=-1 is set, no animation support

Audio

Seeking should be sample-accurate with most codecs in AVI, MKV, MP4 and FLV. Decoding linearly will almost always give correct results, and forward-seeks from trimming should result in at most a few hundred samples of corruption.

Indexing and You

Before FFMS2 can open a file, it must be indexed first so that keyframe/sample positions are known and seeking is easily accomplished. This is done automatically when using FFVideoSource() or FFAudioSource(), but if you want to you can invoke the indexing yourself by calling FFIndex(), or by running ffmsindex.exe. By default the index is written to a file so it can be reused the next time you open the same file, but this behavior can be turned off if desired.

If you wonder why FFMS2 takes so long opening files, the indexing is the answer. If you want a progress report on the indexing, you can use the supplied ffmsindex.exe commandline program.

Function reference

FFIndex

FFIndex(string source, string cachefile = source + ".ffindex", int indexmask = -1,
    int errorhandling = 3, bool overwrite = false, bool enable_drefs = false, bool use_absolute_path = false)

Indexes a number of tracks in a given source file and writes the index file to disk, where it can be picked up and used by FFVideoSource or FFAudioSource. Normally you do not need to call this function manually; it's invoked automatically if necessary by FFVideoSource/FFAudioSource. It does, however, give you more control over how indexing is done.

Note that this function returns an integer, not a clip (since it doesn't open video, nor audio). The return value isn't particularly interesting, but for the record it's 0 if the index file already exists (and is valid) and overwrite was not enabled, 1 if the index file was created and no previous index existed, and 2 if the index file was created by overwriting an existing, valid index file.

Arguments

string source

The source file to index.

string cachefile = source + ".ffindex"

The filename of the index file (where the indexing data is saved). Defaults to sourcefilename.ffindex.

int indexmask = -1

A binary mask representing what audio tracks should be indexed (all video tracks are always indexed; you have no choice in the matter). The mask is constructed by bitshifting 1 left by the track number; if multiple tracks are desired, bitwise OR each value so created together to get the full mask. In other words, the mask is a bit field where each bit is a track number (the least significant bit is track number 0). Since Avisynth doesn't have any bitwise operators at all, constructing a mask for more than one track inside an Avisynth script is a rather annoying task; for a single track the mask is, naturally, 2 to the power of the track number minus 1 (i.e. if you want to index track 3, the mask is 2^(3-1) = 4).

Since the mask works like it does, and FFMS2 is designed to run on a machine that uses two's complement integers, -1 (the default) means index all tracks and 0 means index none.

Note that FFMS2's idea about what track has what number may be completely different from what any other application might think, and that track numbering starts from 1.

int errorhandling = 3

Controls what happens if an audio decoding error is encountered during indexing. Possible values are:

0: Raise an error and abort indexing. No index file is written.
1: Clear the affected track (effectively making it silent) and continue.
2: Stop indexing the track but keep all the index entries so far, effectively ending the track where the error occured.
3: Pretend it's raining and continue anyway. This is the default; if you encounter odd noises in the audio, try mode 0 instead and see if it's FFMS2's fault.

bool overwrite = false

If set to true, FFIndex() will reindex the source file and overwrite the index file even if the index file already exists and is valid. Mostly useful for trackmask changes and testing.

bint enable_drefs = False

Corresponds to the FFmpeg demuxer option of the same name. You will know if you need it.

bint use_absolute_path = False

Corresponds to the FFmpeg demuxer option of the same name. You will know if you need it.

FFVideoSource

FFVideoSource(string source, int track = -1, bool cache = true,
    string cachefile = source + ".ffindex", int fpsnum = -1, int fpsden = 1,
    int threads = -1, string timecodes = "", int seekmode = 1,
    int width = -1, int height = -1, string resizer = "BICUBIC",
    string colorspace = "", string varprefix = "")

Opens video. Will invoke indexing of all video tracks (but no audio tracks) if no valid index file is found.

Arguments

string source

The source file to open.

int track = -1

The video track number to open, as seen by the relevant demuxer. Track numbers start from zero, and are guaranteed to be continous (i.e. there must be a track 1 if there is a track 0 and a track 2). -1 means open the first video track. Note that FFMS2's idea about what track has what number may (or may not) be completely different from what some other application might think. Trying to open an audio track with FFVideoSource will naturally fail.

bool cache = true

If set to true (the default), FFVideoSource will first check if the cachefile contains a valid index, and if it does, that index will be used. If no index is found, all video tracks will be indexed, and the indexing data will be written to cachefile afterwards. If set to false, FFVideoSource will not look for an existing index file; instead all video tracks will be indexed when the script is opened, and the indexing data will be discarded after the script is closed; you will have to index again next time you open the script.

string cachefile = source + ".ffindex"

The filename of the index file (where the indexing data is saved). Defaults to sourcefilename.ffindex. Note that if you didn't change this parameter from its default value and FFVideoSource encounters an index file that doesn't seem to match the file it's trying to open, it will automatically reindex and then overwrite the old index file. On the other hand, if you do change it, FFVideoSource will assume you have your reasons and throw an error instead if the index doesn't match the file.

int fpsnum = -1, int fpsden = 1

Controls the framerate of the output; used for VFR to CFR conversions. If fpsnum is less than or equal to zero (the default), the output will contain the same frames that the input did, and the frame rate reported to Avisynth will be set based on the input clip's average frame duration. If fpsnum is greater than zero, FFVideoSource will force a constant frame rate, expressed as a rational number where fpsnum is the numerator and fpsden is the denominator. This may naturally cause FFVideoSource to drop or duplicate frames to achieve the desired frame rate, and the output is not guaranteed to have the same number of frames that the input did.

int threads = -1

The number of decoding threads to request from libavcodec. Setting it to less than or equal to zero means it defaults to the number of logical CPU's reported by Windows. Note that this setting might be completely ignored by libavcodec under a number of conditions; most commonly because a lot of decoders actually do not support multithreading.

string timecodes = ""

Filename to write Matroska v2 timecodes for the opened video track to. If the file exists, it will be truncated and overwritten. Set to the empty string to disable timecodes writing (this is the default).

int seekmode = 1

Controls how seeking is done. Mostly useful for getting uncooperative files to work. Valid modes are:

-1: Linear access without rewind; i.e. will throw an error if each successive requested frame number isn't bigger than the last one. Only intended for opening images but might work on well with some obscure video format.
0: Linear access (i.e. if you request frame n without having requested all frames from 0 to n-1 in order first, all frames from 0 to n will have to be decoded before n can be delivered). The definition of slow, but should make some formats "usable".
1: Safe normal. Bases seeking decisions on the keyframe positions reported by libavformat.
2: Unsafe normal. Same as mode 1, but no error will be thrown if the exact seek destination has to be guessed.
3: Aggressive. Seeks in the forward direction even if no closer keyframe is known to exist. Only useful for testing and containers where libavformat doesn't report keyframes properly.

int width = -1, int height = -1

Sets the resolution of the output video, in pixels. Setting either dimension to less than or equal to zero means the resolution of the first decoded video frame is used for that dimension. These parameters are mostly useful because FFMS2 supports video streams that change resolution mid-stream; since Avisynth does not, these parameters are used to set single resolution for the output.

string resizer = "BICUBIC"

The resizing algorithm to use if rescaling the image is necessary. If the video uses subsampled chroma but your chosen output colorspace does not, the chosen resizer will be used to upscale the chroma planes, even if you did not request an image rescaling. The available choices are FAST_BILINEAR, BILINEAR, BICUBIC (default), X, POINT, AREA, BICUBLIN, GAUSS, SINC, LANCZOS and SPLINE. Note that SPLINE is completely different from Avisynth's builtin Spline resizers.

string colorspace = ""

Convert the output from whatever it was to the given colorspace, which can be one of YV12, YV16, YV24, Y8, YUY2, YV411, YUV9, RGB24 or RGB32. They can also be referred to with the more systematic names of YUVsssPx, YUVAsssPx, Yx, RGBPx or RGBAPx where x is the desired bitdepth and sss represents the subsampling. Formats with an A also have an alpha channel. Examples: YUV420P8, RGBAP16, Y16 Setting this to an empty string (the default) means keeping the same colorspace as the input or in case it's not supported it'll be converted to the closest existing match.

string varprefix = ""

A string that is added as a prefix to all exported Avisynth variables. This makes it possible to differentiate between variables from different clips. For convenience the last used FFMS function in a script sets the global variable FFVAR_PREFIX to its own variable prefix so that FFInfo() can default to it.

FFAudioSource

FFAudioSource(string source, int track = -1, bool cache = true,
    string cachefile = source + ".ffindex", int adjustdelay = -1,
    int fillgaps = -1, float drc_scale = 0,
string varprefix = "")

Opens audio. Invokes indexing of all tracks if no valid index file is found, or if the requested track isn't present in the index.

Arguments

Are exactly the same as to FFVideoSource, but with these additional options:

int adjustdelay = -1

Controls how audio delay is handled, i.e. what happens if the first audio sample in the file doesn't have a timestamp of zero. The following arguments are valid:

-3: No adjustment is made; the first decodable audio sample becomes the first sample in the output.
-2: Samples are created (with silence) or discarded so that sample 0 in the decoded audio starts at time zero.
-1: Samples are created (with silence) or discarded so that sample 0 in the decoded audio starts at the same time as frame 0 of the first video track. This is the default, and probably what most people want.
Any integer >= 0: Same as -1, but adjust relative to the video track with the given track number instead. If the provided track number isn't a video track, an error is raised.

-2 obviously does the same thing as -1 if the first video frame of the first video track starts at time zero. In some containers this will always be the case, in others (most notably 188-byte MPEG TS) it will almost never happen.

int fillgaps = -1

Determines how audio with discontinuous timestamps are handled.

-1: Apply zero filled gaps to audio in containers where it's usually necessary.
0: Never zero fill gaps.
1: Always zero fill gaps.

float drc_scale = 0

Controls the amount of DRC that's applied to (E)AC-3 audio. 0 means no DRC and 1 means fully applied DRC in accordance with how it's flagged in the stream.

FFmpegSource2/FFMS2

FFmpegSource2/FFMS2(string source, int vtrack = -1, int atrack = -2, bool cache = true,
    string cachefile = source + ".ffindex", int fpsnum = -1, int fpsden = 1,
    int threads = -1, string timecodes = "", int seekmode = 1,
    bool overwrite = false, int width = -1, int height = -1,
    string resizer = "BICUBIC", string colorspace = "",
    int adjustdelay = -1, string varprefix = "")

A convenience function that combines the functionality of FFVideoSource and FFAudioSource. The arguments do the same thing as in FFVideoSource and FFAudioSource; see those functions for details. vtrack and atrack are the video and audio track to open, respectively; setting atrack <= -2 means audio is disabled.

Note: the shorter FFMS2 alias was added in 2.22

FFImageSource

FFImageSource(string source, int width = -1, int height = -1,
    string resizer = "BICUBIC", string colorspace = "")

A convenience alias for FFVideoSource, with the options set optimally for using it as an image reader. Disables caching and seeking for maximum compatiblity.

FFInfo

FFInfo(clip c, bool framenum = true, bool frametype = true, bool cfrtime = true,
    bool vfrtime = true, string varprefix = "", bool colorspace = true,
    bool colorrange = true, bool cropping = true, bool sar =true, bool version = true,
    bool showprefix = false)

A helper function similar to Avisynth's internal Info() function; shows general information about the current frame. Note that not all values are exported in all source modes, so some information may not always be shown. The arguments can be used to disable the drawing of certain information if so desired. Use the varprefix argument to determine which clip you want information about.