コード

from mcap.reader import make_reader
from mcap_ros2.decoder import DecoderFactory
from tqdm import tqdm


mcap_file = "hoge.mcap"

topic_sizes = {}

with open(mcap_file, "rb") as f:
    reader = make_reader(f, decoder_factories=[DecoderFactory()])
    for schema, channel, message, ros_msg in tqdm(reader.iter_decoded_messages(), dynamic_ncols=True):
        topic = channel.topic
        msg_size = len(message.data)

        if topic not in topic_sizes:
            topic_sizes[topic] = 0
        topic_sizes[topic] += msg_size

for topic, size in topic_sizes.items():
    # バイトからMBに変換
    size_mb = size / (1024 * 1024)
    print(f"Topic: {topic}, Size: {size_mb:.2f} MB")

print(f"Total size: {sum(topic_sizes.values()) / (1024 * 1024):.2f} MB")

実行結果

383109it [01:09, 5543.74it/s]
Topic: /topic1, Size: 3.01 MB
Topic: /topic2, Size: 4.02 MB
Total size: 7.03 MB