# Playing a video file from .avs (Avisynth)
- Video players such as mpc-hc/be can play .avs files.
- Frameservers such as Avisynth can be used to process video (they are widely used pre-encoding).
So, can you process video files for realtime display using .avs and is there any benefit to do so ?
Avisynth processing is done primarily on the cpu vs pixel shaders, which use gpu processing.
- For many basic video related operations this is less efficient, even with multi-threading, but it also has fewer limitations.
- Avisynth scripts rely mainly on high quality existing internal/external functions/libraries (compiled .dll C++ plugins).
.avs Display Pipeline:
Video file (.mp4, ex: x264/x265 1080p,
YUV420)
>> .avs: source Filter(video_filename):
Avisynth cpu processing: Output (ex: YV12 or RGB32)
>> Input of Video Player: Video Player processing
(RGB), ex: gpu pixel shaders
>> Monitor (RGB)
Performance:
- as expected, significant cpu overhead with an .avs script vs normal playing.
Depending on the Avisynth filters used, realtime playback may however be achieveable.
- Avisynth filters can be used in complement to gpu pixel shaders.
Software configuration: Win10 x64
- DirectShow Video player: Mpc-be x64, EVR-CP renderer
- Avisynth+ v3.6.1 x64
- external Source plugin: LSMASHSource.dll x64, based on libavcodec, with gpu hw decoding support.
My tests were performed with Avisynth, but the more recent python script alternative Vapoursynth looks promising. It offers direct access to the python software stack (ex: numpy vector math, matplotlib plots, etc.).
## Limitations:
- LSMASHVideoSource / LSMASHAudioSource only support mp4/mov input ! Wider input file format support is available (ex: mkv) with LWLibavVideoSource, but input file must initially be indexed (ex: 10s) !
- video_filename is typically changed by editing the .avs script ! To avoid this, video_filename.avs can be coded so as to load video_filename.mp4 by default.
- On script syntax error, you only get
"Cannot render the File" message in video player ! To get full error msg you need to use either AvsPmod, Virtualdub2 or AvsMeter.
Conclusion:
It is currently possible, but not very practical to play an avs script in a video player. This would probably only make sense if the same effect was not possible as a pixel shader and an equivalent player feature was not available.
Using a per-file script does mean file-specific processing settings are saved. Undesirable lossy re-encoding of a compressed source may be avoided.
Avisynth input can however be useful as a test tool for video:
- YUV-to-RGB colorspace conversion can be performed in Avisynth (with rec709 range expansion by default). In this case the YUV-to-RGB conversion at the video player input is bypassed.
- Resize frame
- Generate test-patterns (ex: ColorBarsHD).
- Go to a specific frame (
vs Directshow video player: seeking is not guaranteed to be frame accurate !).
- Supports multiple video inputs. You could also use multiple clips from the same source (ex: could be used for a split-screen effect or to highlight differences)
- Load/process/save images (ex: lossless .png screenshots) with the same code.
- Output data files (ex: .csv)