Loop in Python and write to a Nested JSON array

This is for a video editing app, where we have several tracks that can house a clip or clips.
What we want to extract, is a JSON file, with all the information related to the starting frame / end frame of each clip.
While we have that when using one clip, the issue is while using multiple clips, the iteration overwrites the previous clip, instead of creating a new JSON object in the array.

Here's the JSON results we currently have:

{
"framesPerSecond": 24,
"StartFrame": 1,
"lastFrame": 1293,
"clip_element": [
{
"clip_name": "",
"track_info": [
{
"start": 1,
"first": 1, #where this clip starts playing
"last": 1293, #frame which the clip ends
"hold_last": "0" #not in use at the moment.
}
],
"transitions": "none" #not in use at the moment.
}
]
}

Adding another clip on a different track, we expect to have another JSON object with "clip_name", "track_info" like this:

"clip_element": [
{
"clip_name": "",
"track_info": [
{
"start": 1,
"first": 1, #where this clip starts playing
"last": 891, #frame which the clip ends
"hold_last": "0" #not in use at the moment.
}
],
"transitions": "none" #not in use at the moment.
},
{
"clip_name": "",
"track_info": [
{
"start": 891,
"first": 892, #where this clip starts playing
"last": 1293, #frame which the clip ends
"hold_last": "0" #not in use at the moment.
}
],
"transitions": "none" #not in use at the moment.
},

Instead the 2nd clip, overwrites the first one, without creating an new JSON object, which mainly is due to hardcoded pointer towards the JSON in our code.

The implementation for reference:

all_tracks = get_app().project.get("layers")
track_count = 0
json_data = track_dict
for track in reversed(sorted(all_tracks, key=itemgetter('number'))):
existing_track = Track.get(number=track.get("number"))
if not existing_track:
log.error('No track object found with number: %s' % track.get("number"))
continue
# Track name
track_name = track.get("label")
clips_on_track = Clip.filter(layer=track.get("number"))
if not clips_on_track:
continue
with open("%s-%s.json" % (file_path.replace(".json", ""), track_name), 'w', encoding="utf8") as f:
# Loop through clips on this track
for index, clip in enumerate(clips_on_track, start=1):
start_frame = codeToFrames(clip.data.get('start'), fps_num, fps_den)
end_frame = codeToFrames(clip.data.get('end'), fps_num, fps_den)
start_frame_position = codeToFrames(clip.data.get('position'), fps_num, fps_den)
end_frame_position = codeToFrames(clip.data.get('position') + (clip.data.get('end') - clip.data.get('start')), fps_num, fps_den)
clip_end_frame = timecodeToFrames(clip.data.get('position') + (clip.data.get('end')), fps_num, fps_den)
has_video = clip.data.get("reader", {}).get("has_video", False)
if has_video:
track_count += 1
index += 1
json_data['FramesPerSecond'] = fps_num
json_data['StartFrame'] = round(start_frame)
json_data['LastFrames'] = round(end_frame_position)
json_data['clip_element'][0]['clip_name'] = track_name
json_data['clip_element'][0]['track_info'][0]['start'] = round(start_frame) + 1 
json_data['clip_element'][0]['track_info'][0]['first'] = round(start_frame_position)
json_data['clip_element'][0]['track_info'][0]['last'] = round(clip_end_frame)
json_data['clip_element'][0]['track_info'][0]['hold_last'] = round(clip_end_frame)
json.dump(json_data, f, indent=4)

We tried by creating a list to hold the data, and using a nested for loop to go through each clip on the track, but it seems that didn't work, as appending the data back again didn't stored the expected results. (syntax issues)

Because this seems to require a for loop for each key (start_frame), (end_frame) etc. is crucial to get the syntax right, which is why we're posting it here.

UPDATE:
The .append worked and created a new JSON object when there's more than 1 clips on the track!
Also, I modified it a little to also append the "clip_name" as well.

{
"framesPerSecond": 24,
"StartFrame": 1,
"lastFrame": 1327,
"clip_element": [
{
"clip_name": "",
"track_info": {
"start": 1,
"first": 0,
"last": 701,
"hold_last": 701
},
"transition": "none"
},
{
"clip_name": "",
"track_info": {
"start": 1,
"first": 626,
"last": 1327,
"hold_last": 1327
},
"transition": "none"
}
]
}

I'm going to guess the problem is these lines:

json_data['clip_element'][0]['clip_name'] = track_name
json_data['clip_element'][0]['track_info'][0]['start'] = round(start_frame) + 1 
json_data['clip_element'][0]['track_info'][0]['first'] = round(start_frame_position)
json_data['clip_element'][0]['track_info'][0]['last'] = round(clip_end_frame)
json_data['clip_element'][0]['track_info'][0]['hold_last'] = round(clip_end_frame)

json_data['clip_element'][0]['track_info'] is an array and json_data['clip_element'][0]['track_info'][0] is the first element in that array. So you're always overwriting the first element.

Instead, you want to append to the array. Probably something like this:

json_data['clip_element'][0]['clip_name'] = track_name
json_data['clip_element'][0]['track_info'].append(
{
'start': round(start_frame) + 1,
'first': round(start_frame_position),
'last': round(clip_end_frame),
'hold_last': round(clip_end_frame),
}
)

I can't run this code in the same context as you're running yours so I can't test this sample.