Video Playback: Difference between revisions

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Note that the Lab Computer displays are typically set to 1920×1080 at 120Hz. We found that this is sufficient for most applications. There are possibilities to go higher. Later in this wiki we will explain how to build audio and video. We will start with playing video, both with and without audio.  
Note that the Lab Computer displays are typically set to 1920×1080 at 120Hz. We found that this is sufficient for most applications. There are possibilities to go higher. Later in this wiki we will explain how to build audio and video. We will start with playing video, both with and without audio.  


=== Python ===
=== Python psychopy 2024.2.4===
Example demonstrating how to play a video with audio:
Example demonstrating how to play a video with audio:
<syntaxhighlight lang="python" line>
<syntaxhighlight lang="python" line>
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win = visual.Window(size=(1024, 768), fullscr=False, color=(0, 0, 0))
win = visual.Window(size=(1024, 768), fullscr=False, color=(0, 0, 0))


video = visual.VlcMovieStim(
movie = visual.MovieStim(
     win, filename=video_file,
     win, filename=video_file,
     autoStart= False
     autoStart= False
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# Main loop for video playback
# Main loop for video playback
while video.status != visual.FINISHED:
while not movie.isFinished:
     # Draw the current video frame
     # Draw the current video frame
     video.draw()
     movie.draw()
     win.flip()
     win.flip()


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     if 'q' in keys:
     if 'q' in keys:
         break
         break
movie.stop()    # stop playback
del movie
gc.collect()


win.close()
win.close()
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</syntaxhighlight>
</syntaxhighlight>


Example demonstrating how to play a video with audio disconected:
Example demonstrating how to play a video with audio disconnected:
<syntaxhighlight lang="python" line>
<syntaxhighlight lang="python" line>
from psychopy import logging, prefs
from psychopy import logging, prefs
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win = visual.Window(size=(1280, 720), fullscr=False, color=(0, 0, 0), units="pix")
win = visual.Window(size=(1280, 720), fullscr=False, color=(0, 0, 0), units="pix")


video = visual.VlcMovieStim(
movie = visual.MovieStim(
     win, filename=video_file,
     win, filename=video_file,
     size=None,  # Use the native video size
     size=None,  # Use the native video size
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audio.play()
audio.play()
time.sleep(0.04)
time.sleep(0.04)
video.play()
movie.play()
video_start_time = core.getTime()
movie_start_time = core.getTime()


while video.status != visual.FINISHED:
while not movie.isFinished:
     # Draw the current video frame
     # Draw the current video frame
     video.draw()
     movie.draw()
     win.flip()
     win.flip()


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         audio.stop()
         audio.stop()
         break
         break
movie.stop()    # stop playback
del movie
gc.collect()


# Close the PsychoPy window
# Close the PsychoPy window
win.close()
win.close()
core.quit()
core.quit()
</syntaxhighlight>
Example demonstrating if video and audio encoding are correct:
<syntaxhighlight lang="python" line>
import subprocess
import json
file_path = "tick_rhythm_combined_1min.mp4"
def check_video_file(file_path):
    try:
        # Run ffprobe to get file metadata in JSON format
        result = subprocess.run(
            [
                "ffprobe",
                "-v", "error",
                "-show_streams",
                "-show_format",
                "-print_format", "json",
                file_path
            ],
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True
        )
        metadata = json.loads(result.stdout)
    except Exception as e:
        print(f"Error running ffprobe: {e}")
        return
   
    # Check for video stream
    video_stream = next((stream for stream in metadata['streams'] if stream['codec_type'] == 'video'), None)
    if video_stream:
        # Check video codec
        video_codec = video_stream.get('codec_name')
        if video_codec == 'h264':
            print("Video codec: H.264")
        else:
            print(f"ERROR: Video codec is NOT H.264 (Found: {video_codec})")
        # Extract and report frame rate
        if 'r_frame_rate' in video_stream:
            raw_frame_rate = video_stream['r_frame_rate']
            calculated_frame_rate = eval(raw_frame_rate)  # Convert string like "30/1" to float
            print(f"Frame rate: {calculated_frame_rate:.2f} FPS (raw: {raw_frame_rate})")
        else:
            print("ERROR: Could not determine raw frame rate from metadata.")
        # Check for constant frame rate
        if video_stream.get('avg_frame_rate'):
            avg_frame_rate = eval(video_stream['avg_frame_rate'])
            if abs(avg_frame_rate - calculated_frame_rate) < 0.01:
                print("Frame rate: Constant")
            else:
                print(f"ERROR: Frame rate is NOT constant (avg_frame_rate: {avg_frame_rate:.2f} FPS)")
        else:
            print("ERROR: Could not determine average frame rate consistency.")
       
        # Check for frame drops
        try:
            frame_info_result = subprocess.run(
                [
                    "ffprobe",
                    "-v", "error",
                    "-select_streams", "v:0",
                    "-show_entries", "frame=pkt_pts_time",
                    "-of", "csv=p=0",
                    file_path
                ],
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
                text=True
            )
            # Filter out empty or invalid lines
            frame_times = [
                float(line.strip()) for line in frame_info_result.stdout.splitlines()
                if line.strip()  # Exclude empty lines
            ]
            expected_interval = 1.0 / calculated_frame_rate  # Expected time between frames
            frame_drops = [
                i for i, (t1, t2) in enumerate(zip(frame_times, frame_times[1:]))
                if abs(t2 - t1 - expected_interval) > 0.01  # Tolerance for irregularity
            ]
            if frame_drops:
                print(f"ERROR: Detected frame drops at frames: {frame_drops}")
            else:
                print("No frame drops detected.")
        except Exception as e:
            print(f"Error analyzing frames for drops: {e}")
    else:
        print("ERROR: No video stream found")
   
    # Check for audio stream
    audio_stream = next((stream for stream in metadata['streams'] if stream['codec_type'] == 'audio'), None)
    if audio_stream:
        # Check audio codec
        audio_codec = audio_stream.get('codec_name')
        if audio_codec == 'pcm_s16le':
            print("Audio codec: WAV (PCM)")
        else:
            print(f"ERROR: Audio codec is NOT WAV (PCM) (Found: {audio_codec})")
       
        # Check sample rate
        sample_rate = audio_stream.get('sample_rate')
        if sample_rate == "44100":
            print("Audio sample rate: 44.1 kHz")
        else:
            print(f"ERROR: Audio sample rate is NOT 44.1 kHz (Found: {sample_rate} Hz)")
    else:
        print("ERROR: No audio stream found")
   
    # Check synchronization
    if video_stream and audio_stream:
        video_start_pts = float(video_stream.get('start_time', 0))
        audio_start_pts = float(audio_stream.get('start_time', 0))
        if abs(video_start_pts - audio_start_pts) < 0.01:  # Tolerance for synchronization
            print("Video and audio are synchronized.")
        else:
            print(f"ERROR: Video and audio are NOT synchronized. Start difference: {abs(video_start_pts - audio_start_pts):.3f} seconds")
    else:
        print("ERROR: Could not determine synchronization (missing video or audio streams).")
# Example usage
if __name__ == "__main__":
    check_video_file(file_path)


</syntaxhighlight>
</syntaxhighlight>
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subprocess.run(['ffmpeg', '-i', input_file, '-an', output_video])
subprocess.run(['ffmpeg', '-i', input_file, '-an', output_video])


subprocess.run(['ffmpeg', '-i', input_file, '-vn', '-acodec', 'pcm_s16le', '-ar', '44100', output_audio])
subprocess.run(['ffmpeg', '-i', input_file, '-vn', '-acodec', 'pcm_s16le', '-ar', '48000', output_audio])


print(f"Video saved to: {output_video}")
print(f"Video saved to: {output_video}")
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Stabilize the camera and avoid automatic exposure, white balance, or focus during recording to prevent inconsistencies.
Stabilize the camera and avoid automatic exposure, white balance, or focus during recording to prevent inconsistencies.
Record in a controlled environment with consistent lighting and minimal background distractions.
Record in a controlled environment with consistent lighting and minimal background distractions.
You can use the '''facecam''' for high quality video recording.
The TSG recomends to use the [[Elgato Facecam]] for high quality video recording.


===Video Settings===
===Video Settings===
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|-
|-
!File format  
!File format  
|.mp4 (H.264 codec(libx264)) ik wil hier een link naar de dll?
|.mp4 (H.264 [[media:Openh264-1.8.0-win64_.zip | codec(libx264)]])  
|-
|-
!Frame rate  
!Frame rate  
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=== Python ===
=== Python ===
Example demonstrating how to check and play your audio:
Example demonstrating how to check your os settings, audio file and play your audio:
<syntaxhighlight lang="python" line>
<syntaxhighlight lang="python" line>
#!/usr/bin/env python3.10
#!/usr/bin/env python3.10
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==FFmpeg==
==FFmpeg==
{{See also|FFmpeg}}
===Synchronization===
===Synchronization===
Ensure the audio and video streams have consistent timestamps:  
Ensure the audio and video streams have consistent timestamps:  
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Here’s a command that encodes video and audio while maintaining high time accuracy:
Here’s a command that encodes video and audio while maintaining high time accuracy:
<pre>
<pre>
ffmpeg -i input.mp4 -c:v libx264 -preset slow -crf 18 -vsync cfr -g 30 -c:a pcm_s16le -ar 44100 -fflags +genpts -async 1 output.mp4
ffmpeg -i input.mp4 -c:v libx264 -preset slow -crf 18 -vsync cfr -g 30 -c:a pcm_s16le -ar 48000 -fflags +genpts -async 1 output.mp4
-c:v libx264: Encode video using H.264.
-c:v libx264: Encode video using H.264.
-preset slow: Optimize for quality and compression efficiency.
-preset slow: Optimize for quality and compression efficiency.
Retrieved from "https://tsgdoc.socsci.ru.nl/index.php/Video_Playback"