[GOWS] - FFmpeg Thumbnail Generation Error in GOWS v1.0.26



## Summary

**Issue**: Video thumbnail generation fails when processing video messages due to incorrect FFmpeg output format.

**Severity**: High - Affects all video message processing in GOWS engine

**Version**: GOWS v1.0.26

**Environment**: Docker container running on Debian 12, FFmpeg 5.1.8

---

## Error Description

When the GOWS engine processes video messages (received or sent), it attempts to generate a 72px thumbnail using FFmpeg. The command fails with the following error:

```
[image2 @ 0x5564f0501e80] The specified filename 'pipe:' does not contain an image sequence pattern or a pattern is invalid.
[image2 @ 0x5564f0501e80] Use a pattern such as %03d for an image sequence or use the -update option (with -frames:v 1 if needed) to write a single image.
```

---

## Root Cause

The FFmpeg command uses `-f image2` format, which is designed for **writing to files**, not pipes. When the output is a pipe (`pipe:`), the `image2` muxer expects a filename pattern (e.g., `frame%03d.jpg`) or the `-update` flag.

### Problematic Command

```bash
ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -f image2 -vframes 1 pipe: -y
```

**Issue**: Using `-f image2` with `pipe:` output

---

## Complete Error Logs

```log
2025/12/21 07:58PM 30 pid=7 hostname=27e7d92ff134 session=11_16_5551997658394 
name=WebhookSender id=402wek7mjgbw0os event.id=evt_01kd1j59kwn1dq0kckk3j06rx4 
event=message.ack url=https://chat.gowdy.com.br/webhooks/whatsapp/+5551997658394 
msg=Sending POST...

2025/12/21 07:58PM 30 pid=7 hostname=27e7d92ff134 session=11_16_5551997658394 
name=WebhookSender id=402wek7mjgbw0os event.id=evt_01kd1j59kwn1dq0kckk3j06rx4 
event=message.ack url=https://chat.gowdy.com.br/webhooks/whatsapp/+5551997658394 
msg=POST request was sent with status code: 200

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=2025/12/21 19:58:23 compiled command: ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -f image2 -vframes 1 pipe: -y

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=ffmpeg version 5.1.8-0+deb12u1 Copyright (c) 2000-2025 the FFmpeg developers
  built with gcc 12 (Debian 12.2.0-14+deb12u1)
  ...
  libavutil      57. 28.100 / 57. 28.100
  libavcodec     59. 37.100 / 59. 37.100
  libavformat    59. 27.100 / 59. 27.100
  ...

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'pipe:0':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : 4090302881254490
    encoder         : Lavf59.27.100
  Duration: 00:00:31.84, start: 0.000000, bitrate: N/A
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 360x640, 522 kb/s, 30 fps, 30 tbr, 15360 tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
      encoder         : Lavc59.37.100 libx264
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=Stream mapping:
  Stream #0:0 (h264) -> scale:default
  select:output0 -> Stream #0:0 (mjpeg)

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=[swscaler @ ...] deprecated pixel format used, make sure you did set range correctly

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=Output #0, image2, to 'pipe:':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : 4090302881254490
    encoder         : Lavf59.27.100
  Stream #0:0: Video: mjpeg, yuvj420p(pc, bt709, progressive), 72x128, q=2-31, 200 kb/s, 30 fps, 30 tbn
    Metadata:
      encoder         : Lavc59.37.100 mjpeg
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: N/A

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=[image2 @ 0x5564f0501e80] The specified filename 'pipe:' does not contain an image sequence pattern or a pattern is invalid.
[image2 @ 0x5564f0501e80] Use a pattern such as %03d for an image sequence or use the -update option (with -frames:v 1 if needed) to write a single image.

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=frame=    1 fps=0.0 q=2.7 size=N/A time=00:00:00.03 bitrate=N/A speed=2.77x    

2025/12/21 07:58PM 50 pid=7 hostname=27e7d92ff134 engine=gows 
msg=frame=    1 fps=0.0 q=2.7 Lsize=N/A time=00:00:00.03 bitrate=N/A speed=0.765x
```

---

## Analysis

### What Works
✅ FFmpeg is correctly installed (version 5.1.8)  
✅ Video input is successfully read from pipe (H.264, 360x640, 31.84s)  
✅ Audio stream is detected (AAC, stereo, 44.1kHz)  
✅ Filter complex correctly scales video to 72x128  
✅ Frame is successfully extracted and encoded to MJPEG  

### What Fails
❌ The `image2` muxer rejects writing to a pipe without a filename pattern

### Impact
- Video thumbnails are not generated
- WhatsApp messages may be incomplete (thumbnails are part of the protocol)
- Webhook notifications may fail or send incomplete data
- User experience is degraded (no video preview)

---

## Proposed Solutions

### Solution 1: Use `image2pipe` Format (Recommended)

**Change the command from:**
```bash
ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -f image2 -vframes 1 pipe: -y
```

**To:**
```bash
ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -vframes 1 -f image2pipe pipe: -y
```

**Key changes:**
- Remove `-f image2`
- Add `-f image2pipe` before the output
- Reorder: `-vframes 1 -f image2pipe pipe:`

**Why this works:**  
`image2pipe` is specifically designed for piping single images, unlike `image2` which expects file sequences.

---

### Solution 2: Add `-update` Flag

**Change the command to:**
```bash
ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -f image2 -update 1 -vframes 1 pipe: -y
```

**Key change:**
- Add `-update 1` flag

**Why this works:**  
The `-update 1` flag tells `image2` to write a single image without requiring a pattern.

---

### Solution 3: Use MJPEG Format Directly

**Change the command to:**
```bash
ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -vframes 1 -c:v mjpeg -f mjpeg pipe: -y
```

**Key changes:**
- Explicitly specify codec: `-c:v mjpeg`
- Use MJPEG format: `-f mjpeg`

**Why this works:**  
MJPEG format naturally supports single-frame output to pipes.

---

## Recommendation

**Use Solution 1** (`-f image2pipe`) as it:
- Is the most semantically correct for the use case
- Has minimal changes to the existing command
- Is well-documented and widely supported
- Is the standard approach for piping images in FFmpeg

---

## Code Location

The FFmpeg command is generated in the **GOWS Go source code** (repository: `devlikeapro/gows`, version `v1.0.26`).

The command is likely in code related to:
- Thumbnail generation
- Video message processing
- Media preprocessing for WhatsApp protocol

Search for:
```go
"scale=72:-1"
"-f image2"
"pipe:"
```

---

## Testing

After applying the fix, verify with:

```bash
# Test command directly
echo "test_video.mp4" | ffmpeg -i pipe:0 -filter_complex [0]scale=72:-1[s0];[s0]select=gte(n\,0)[s1] -map [s1] -vframes 1 -f image2pipe pipe: -y > thumbnail.jpg

# Should create a valid 72px wide JPEG
file thumbnail.jpg  # Should show: JPEG image data
```

---

## Additional Notes

### Video Details from Error Log
- **Format**: MP4 (H.264 video + AAC audio)
- **Resolution**: 360x640 (portrait/vertical)
- **Duration**: 31.84 seconds
- **Video Bitrate**: 522 kb/s
- **Audio**: Stereo, 44.1kHz, 128 kb/s
- **FPS**: 30

### Thumbnail Specification
- **Width**: 72 pixels (fixed)
- **Height**: Calculated automatically (maintains aspect ratio)
- **Resulting size**: 72x128 pixels
- **Format**: JPEG (MJPEG codec)
- **Purpose**: WhatsApp message thumbnail/preview

---



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[GOWS] - FFmpeg Thumbnail Generation Error in GOWS v1.0.26 #1746

Summary

Error Description

Root Cause

Problematic Command

Complete Error Logs

Analysis

What Works

What Fails

Impact

Proposed Solutions

Solution 1: Use `image2pipe` Format (Recommended)

Solution 2: Add `-update` Flag

Solution 3: Use MJPEG Format Directly

Recommendation

Code Location

Testing

Additional Notes

Video Details from Error Log

Thumbnail Specification

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Uh oh!

Uh oh!

[GOWS] - FFmpeg Thumbnail Generation Error in GOWS v1.0.26 #1746

Description

Summary

Error Description

Root Cause

Problematic Command

Complete Error Logs

Analysis

What Works

What Fails

Impact

Proposed Solutions

Solution 1: Use image2pipe Format (Recommended)

Solution 2: Add -update Flag

Solution 3: Use MJPEG Format Directly

Recommendation

Code Location

Testing

Additional Notes

Video Details from Error Log

Thumbnail Specification

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Solution 1: Use `image2pipe` Format (Recommended)

Solution 2: Add `-update` Flag