Output video from demo app is missing duration metadata

I'm running into an issue attempting to get the sam2 demo to run properly on a local machine.

I am able to process and download an example file (using the included 01_dog.mp4 as an example), but the output file appears to be missing a lot of metadata, including perhaps most importantly, a duration. The video does play in VLC, but the timeline length shows 00:00 and will not seek to a particular point in time. You can see the same behavior below:

https://github.com/user-attachments/assets/aaf48b4b-1ca6-438c-b1fe-7f6a1f067f72

Looking at the file data in ffmpeg i see some interesting things:

```
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '01_dog_local.mp4':
Metadata:
major_brand : iso4
minor_version : 0
compatible_brands: iso4
Duration: 00:00:00.04, start: 0.000000, bitrate: 728985 kb/s
Stream #0:0[0x1](eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(progressive), 1280x720, 3134 kb/s, 24 fps, 60 tbr, 90k tbn (default)
Metadata:
handler_name : Track created with MP4Box.js
vendor_id : [0][0][0][0]
encoder : avc1 Compressor
Side data:
displaymatrix: rotation of nan degrees
```

this is in contrast to the raw unprocessed example file:

```
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '01_dog.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
title : My Movie 6
encoder : Lavf61.1.100
keywords : iMovie
Duration: 00:00:09.66, start: 0.000000, bitrate: 1439 kb/s
Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1280x720 [SAR 1:1 DAR 16:9], 1429 kb/s, 29.97 fps, 29.97 tbr, 30k tbn (default)
Metadata:
handler_name : Core Media Video
vendor_id : [0][0][0][0]
encoder : Lavc61.3.100 libx264
timecode : 00:00:00:00
Stream #0:1[0x2](eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 2 kb/s (default)
Metadata:
handler_name : Core Media Audio
vendor_id : [0][0][0][0]
Stream #0:2[0x3](eng): Data: none (tmcd / 0x64636D74), 0 kb/s
Metadata:
handler_name : Core Media Video
timecode : 00:00:00:00
```

....and the output for the same file when using the sam2 online demo at https://sam2.metademolab.com/demo:
```
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '01_dog_online.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf60.16.100
Duration: 00:00:09.63, start: 0.000000, bitrate: 389 kb/s
Stream #0:0[0x1](eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 386 kb/s, 24 fps, 24 tbr, 12288 tbn (default)
Metadata:
handler_name : Track created with MP4Box.js
vendor_id : [0][0][0][0]
encoder : Lavc60.31.102 libx264
```

The stream data appears to be substantially different - does it look like a corrupted encode? I have tried a different encoder (h264_nvenc) but i'm seeing the same result. Is there an issue with the re-encoding of frames that ffmpeg is doing?